http://informahealthcare.com/ceh ISSN: 1064-1963 (print), 1525-6006 (electronic) Clin Exp Hypertens, 2014; 36(8): 567–571 ! 2014 Informa Healthcare USA, Inc. DOI: 10.3109/10641963.2014.881843
ORIGINAL ARTICLE
Cardiovascular function alterations induced by acute paradoxical sleep deprivation in rats F. R. Almeida1*, J. C. Perry2*, H. A. Futuro-Neto3, V. R. Almeida1, R. M. Sebastia˜o1, M. L. Andersen2, S. Tufik2, R. R. Campos1, and C. T. Bergamaschi1 1
Cardiovascular Division, Department of Physiology, Universidade Federal de Sa˜o Paulo, SP, Brazil, 2Department of Psychobiology, Universidade Federal de Sa˜o Paulo, SP, Brazil, and 3Department of Morphology, UFES, EMESCAM and Faculdade Brasileira Medical Schools, ES, Brazil
Abstract
Keywords
Sleep loss has been implicated in triggering the hypertension. The goal of the present study was investigated the possible mechanisms underlying cardiovascular alterations after acute paradoxical sleep deprivation (PSD). Male Wistar rats were assigned in two experimental groups: (1) control and (2) PSD for 24 h using the modified single platform method. Paradoxical sleep deprived rats exhibited higher blood pressure, heart rate (HR) and impaired baroreceptor sensitivity. After pharmacological autonomic double blockade (propranolol and methylatropine administration), intrinsic heart rate was decreased after PSD. The PSD rats showed a reduction in the vagal tone without affecting sympathetic tone. Isoproterenol administration (0.001, 0.01 and 1 mg/kg) induced an increase in DHR responses in PSD group. Electrocardiographic analysis in response to b-adrenergic stimulation indicated that PSD contributed to ventricular cardiac arrhythmias. Our findings suggest that acute paradoxical sleep loss induce cardiovascular alterations, autonomic imbalance accompanied by impaired baroreflex sensitivity and increased arrhythmia susceptibility.
Arrhythmia, heart rate, isoproterenol, paradoxical sleep deprivation, sleep
Introduction Recent studies have shown that either reduced or even increased total sleep time are related to increased cardiovascular risk (1–4). The different stages of sleep affect diversely the autonomic control systems leading to specific cardiovascular adjustments during sleep period (5,6). For instance, during synchronized, non-rapid eye movement sleep (NREM) period, or slow wave sleep, parasympathetic activity to cardiovascular system is predominant leading to reduction of blood pressure (BP), heart rate (HR), cardiac output and peripheral vascular resistance (6–8). Desynchronized, paradoxical or rapid eye movement (REM) period has two distinct phases: tonic and phasic. In the tonic phase, the cardiovascular parameters remain similar to NREM sleep; however, in the phasic stage of REM sleep, there is augmentation in discharges of sympathetic nervous system, linked to rapid and ephemeral increases in skeletal muscle tone. Therefore, in the REM sleep phase, BP and HR reached values similar to those observed during wakefulness (6–8). Considering that sleep deprivation does not allow the natural decline in sympathetic vasomotor tone and blood pressure during sleep, such condition is related to *These authors contributed equally to this work. Correspondence: Ca´ssia T. Bergamaschi, PhD, Cardiovascular Division, Department of Physiology, Universidade Federal de Sa˜o Paulo, Rua Botucatu, 862, CEP 04023-060, Sa˜o Paulo, SP, Brazil. Tel: +55 11 5573 7820 extn 27. Fax: +55 11 5573 7820 extn 5. E-mail: bergamaschi. [email protected]
History Received 3 October 2013 Revised 16 December 2013 Accepted 23 December 2013 Published online 27 March 2014
hyperactivity of the sympathetic nervous system related to changes in cardiovascular regulation (9) and also leading to increase of hypothalamic-pituitary–adrenocortical axis activity (10). Moreover, paradoxical sleep deprivation (PSD) increased circulating catecholamine concentrations (11), modified lipid biosynthesis (12) and increased HR (9,13) and systolic blood pressure (13). We have recently demonstrated that PSD during different periods induces an increase in sympathetic vasomotor activity, preferentially to the kidney, and such alteration was associated with differential modifications in the renin–angiotensin system components (9). However, the mechanisms underlying sympathoexcitation, tachycardia and blood pressure increase induced by PSD are not well understood; in the present study, we tested the hypothesis that changes in the reflex control of circulation by the arterial baroreceptors may play a role. Therefore, despite the fact that several studies have correlated the decrease in amount of sleep with increased cardiovascular risk (1–4), there is little information regarding the precise effects of acute PSD on cardiovascular function. Thus, the present study aimed to evaluate the effects of acute PSD for 24 h on cardiovascular function and the possible mechanisms underlying such alterations in rats.
Methods Animals Experiments were performed in 68 male adult Wistar rats (250–300 g) provided by the Centro de Desenvolvimento
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F. R. Almeida et al.
de Modelos Experimentais para Medicina e Biologia (CEDEME) – Universidade Federal de Sa˜o Paulo. The animals were housed in groups of four in standard polypropylene cages in a room maintained at 22 C with a 12:12 h light–dark cycle (lights on at 07:00 h) and allowed free access to food and water. Rats used in this study were maintained and treated in accordance with the guidelines established by the Ethical and Practical Principles for the Use of Laboratory Animals. All animal procedures were approved by the University Ethics Committee (CEP no 2805/09). Paradoxical sleep deprivation Rats were randomly assigned to one of two experimental groups: (1) control and (2) PSD for 24 h. Two independent series of experiments were performed in control or in rats submitted to PSD. In the first series of experiments, the effects of PSD on cardiovascular function (arterial baroreceptor control of HR and autonomic balance to the heart) were assessed. In the second series of experiments, cardiovascular changes induced by isoproterenol administration (dose–response curve) were investigated. Animals were subjected to PSD for 24 h using the single platform-over-water technique. Rats were individually placed on a circular platform (6.5 cm in diameter) in a cage (23 cm 23 cm 29 cm) filled with water up to 1 cm below the platform level. During paradoxical sleep, rats tend to fall off the platform due to neck muscular atonia and awaken on contact with the water. Moreover, prior to commencement of the PSD protocol, all sleep-deprived animals received a habituation period on the platform (1 h/day for 3 days). After 24 h of PSD, the single platform procedure was effective in producing a total suppression of paradoxical sleep and a reduction in slow wave sleep (34–39%) in rats (14,15). Food and water were provided ad libitum. The control groups were housed in similar individual cages containing bedding and one platform without water. The rats were kept in the same room as the experimental rats during the study. First series of experiments Analysis of cardiovascular function and the control of heart rate by the arterial baroreceptors in conscious rats Immediately after PSD rats were anesthetized with halothane (2% in 100% oxygen-enriched air – during 20 min) and instrumented with femoral venous and arterial catheters for drug injection and arterial pressure recording, respectively. Catheters were externalized through the neck. Cardiovascular measurements were made 4–5 h later and lasted for 20 min. During this period, sleep deprivation was carried out by gentle handling, which involved tapping the cages whenever the animals appeared drowsy. MAP and HR were recorded in conscious rats via the arterial catheter, connected to a pressure transducer and to an analogical digital converter (PowerLab, AD Instruments, Bella Vista, NSW, Australia). Mean arterial pressure (MAP) and HR signals on conscious rats were derived from pulsatile arterial pressure. For arterial baroreceptor reflex function analysis, pressor doses of phenylephrine (3, 5 and 10 mg/kg, IV – Sigma-Aldrich, St. Louis, MO) and depressor dose of sodium nitroprusside (5, 15 and
Clin Exp Hypertens, 2014; 36(8): 567–571
20 mg IV Sigma-Aldrich, St. Louis, MO) were randomly acutely administered in an interval of 15 min to induce progressive increase or decrease of blood pressure and the reflex bradycardia or tachycardia, respectively. The sensitivity of the arterial baroreceptor for HR control was evaluated by the mean index relating changes in HR to changes in MAP and was expressed as beats per mmHg (bpm/mmHg). Values of matching MAP variations with reflex HR responses were plotted separately for each vasoactive drug to create linear regression curves of baroreceptor function for each group, and their slopes were compared to evaluate changes in baroreflex gain. All signals were recorded on a computer-based data acquisition system (PowerLab system, AD Instruments, Bella Vista, NSW, Australia) with a 2-kHz sampling rate. Intrinsic heart rate and autonomic modulation Sympathetic and vagal tones were assessed by autonomic blockade produced by acute injection of propanolol (4 mg/kg; IV – Sigma-Aldrich, St. Louis, MO) and methylatropine (3 mg/kg; IV – Sigma-Aldrich, St. Louis, MO), respectively. The difference between HR calculated at the end of 15 min after the propanolol administration and the basal HR was considered as the sympathetic tone. On the other hand, the difference between the HR calculated at the end of 15 min after methylatropine administration and the basal HR was considered as the vagal tone. The intrinsic heart rate was assessed after dual pharmacological blockade by propanolol and methylatropine. Second series of experiments Isoproterenol dose–response curve Rats were anesthetized with halothane (2% in 100% oxygenenriched air) and instrumented with femoral venous and arterial catheters for drug injection and arterial pressure recording, respectively. For electrocardiogram analysis, two silver electrodes were implanted in the left and in the right side of thorax between the 5th and 6th intercostals space, respectively, externalized through the neck and connected to an AC amplifier (Neuro Log, Digitimer Ltd, Hertfordshire, UK) and a band-pass filter (50–1000 Hz, 2 K sampling rate). All signals were recorded on a computer-based data acquisition system (PowerLab system, AD Instruments, Bella Vista, NSW, Australia). Isoproterenol (Sigma-Aldrich, St. Louis, MO) was injected IV at doses of 0.001, 0.01 and 1 mg/kg. The maximum HR response was observed as well as the total numbers of cardiac arrhythmias (defined as extrabeats followed by a compensatory pause) measured for 10 min after isoproterenol administration in conscious rats. Statistical analyses Student’s t-test for independent samples by group was used to analyze the data. Values are expressed as mean ± SEM. p50.05 was considered statistically significant.
Results Figure 1(A) and (B), respectively, shows that PSD for 24 h resulted in significant increased MAP (C 108 ± 1, n ¼ 12; PSD 123 ± 3 mmHg, n ¼ 12, p50.001) and HR (C 337 ± 6,
DOI: 10.3109/10641963.2014.881843
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Figure 2. (A) Cardiac baroreflex function and the respective slope values correlating mean arterial pressure decrease (DMAP) and the reflex heart rate increase (DHR) induced by sodium nitroprusside (5–20 mg/kg, IV). (B) Cardiac baroreflex function and the respective slope values correlating mean arterial pressure increase (DMAP) and the reflex heart rate decrease (DHR) induced by phenylephrine (3–10 mg/kg, IV). *p50.05 compared to control group (Student’s t-test). C (control/ n ¼ 10); PSD (paradoxical sleep deprivation/n ¼ 12).
and (B), respectively. The PSD group displayed significantly impaired sensitivity of the arterial baroreceptor control of HR for both the depressor and pressor responses. In the second and independent series of experiments, the HR responses to isoproterenol administration were evaluated (0.001, 0.01, 1 mg/kg; Figure 3A). The three progressive doses of isoproterenol induced statistically significant increase in DHR responses in PSD group (87 ± 12; 142 ± 9; 201 ± 8 bpm, p50.05) compared to control group (48 ± 8; 83 ± 16; 138 ± 10 bpm), respectively. Finally, the electrocardiographic analysis demonstrated that the PSD group showed a significant increase in the total number of ventricular cardiac arrhythmias compared to control group after the administration of isoproterenol at doses of 0.001 mg/kg (control 0.83 ± 0.5 and PSD 3.33 ± 1.0 extra beats/10 min) and 1 mg/ kg (control 2.8 ± 2.4 and PSD 10.5 ± 1.7 extra beats/10 min) (Figure 3B). However, no significant difference was found between groups in the intermediate dose (0.01 mg/kg; c: 3.67 ± 2.38 and PSD: 6.0 ± 2.03 extra beats/10 min). Figure 1. Effects of acute paradoxical sleep deprivation on mean arterial pressure (Panel A), heart rate (Panel B) and intrinsic heart rate (Panel C) in rats. *p50.05 compared to control group (Student’s t-test). Data are expressed as mean ± SEM. C (control/n ¼ 12); PSD (paradoxical sleep deprivation/n ¼ 12).
n ¼ 12; PSD 386 ± 5 bpm, n ¼ 12, p50.001) compared to control group. Furthermore, after pharmacological autonomic double blockade with propranolol and methylatropine administration, paradoxical sleep-deprived rats showed a significant reduction in intrinsic heart rate compared to control group (C 420 ± 10, n ¼ 10; PSD 387 ± 6 bpm, n ¼ 12, p50.001; Figure 1C). The PSD group showed a significantly lower vagal tone compared to control group (C 132 ± 15, n ¼ 10 and PSD 61 ± 11 bpm, n ¼ 12; p50.05). However, no significant difference was observed in sympathetic tone (C 34 ± 5, n ¼ 10 and PSD 53 ± 13 bpm, n ¼ 12). The HR baroreceptor reflex functions and the slope values for depressor and pressor responses are shown in Figure 2(A)
Discussion The results of the present study provide evidence that 24 h of PSD can affect cardiovascular function in male Wistar rats. Specifically, acute PSD induced an increase of HR and BP associated with an impairment of the baroreflex control of blood pressure. The PSD rats showed a reduction in the vagal tone and intrinsic heart rate. Finally, the acute PSD leads to an increase cardiovascular sensitivity to b-adrenergic stimulation, and a significant increase in the incidence of ventricular cardiac arrhythmias induced by isoproterenol. Altogether such changes are important mechanisms triggering increased cardiovascular risk induced by PSD. Heart rate and BP were significantly increased in animals submitted to total sleep deprivation and PSD (9,10,13). Other studies showed that deprivation and fragmentation of sleep also generates increases in baseline hemodynamic parameters in humans (16–20). Sauvet et al. (19) observed an increase
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Figure 3. (A) Effects of increasing doses of isoproterenol (0.001, 0.01 and 1 mg/kg, IV) on heart rate (delta) and (B) total number of arrhythmias (arrhythmias/10 min). *p50.05 compared to control group (Student’s t-test). Data are expressed as mean ± SEM. C (control/n ¼ 10); PSD (paradoxical sleep deprivation/n ¼ 12).
in blood pressure only after a period of 36 h of total sleep deprivation, while Kato et al. (17) found an increase in blood pressure without an effect on HR, after 24 h of total sleep deprivation. Moreover, a decrease in HR after 30 h of total sleep deprivation was also reported (18). In humans, the discrepancies between the results in various studies can be at least partially explained by the study conditions, variations in the studies in relation to age, gender and other comorbidities, that may have influence on cardiovascular parameters. However, animal experimentation allows for the assessment of the isolated effects of PSD. Given that a significant impairment of baroreceptor sensitivity was induced in PSD, the effects of sleep on baroreflex response may be relevant to our understanding regarding a major mechanism that triggers increase in sympathetic activity, blood pressure and HR. Changes in sensitivity of the baroreflex response may be considered as an important prognostic marker of impaired functioning of the cardiovascular system. The results of this study demonstrated that paradoxical sleep deprived rats showed altered cardiac baroreflex sensitivity. Studies addressing these issues have provided contrasting results. Sayk et al. (21) and Pagani et al. (22) showed no alteration of baroreflex control after total sleep deprivation in humans. However, Radulovacki et al. (23) demonstrated that rats deprived of
Clin Exp Hypertens, 2014; 36(8): 567–571
paradoxical sleep for 48 h showed an increase in baroreflex sensitivity while Matos et al. (24), observed a reduction in the same parameter. These discrepancies might be in part explained by the fact that most of the studies used different experimental protocols of sleep deprivation in terms of number of hours of sleep loss, study design, experimental settings and population characteristics. Intrinsic heart rate is lower in the PSD group compared to control group. Although the present study did not directly evaluate the mechanisms involved in the generation of pacemaker frequency, we could suggest that the PSD is capable of interfering with these mechanisms by modifying the firing frequency of the sinoatrial node. One hypothesis that explains the alterations after sleep deprivation is the incidence of abnormalities in the gradients of ionic currents, involved in transmembrane depolarization and repolarization of the sinoatrial node (25). Several studies have shown that total sleep deprivation and PSD is associated with sympathetic hyperactivity (9,10,26) and increased circulating catecholamines (11,27,28). In the present study, we assessed the cardiac autonomic balance through double pharmacological autonomic blockade. These results showed that vagal tone was lower after PSD, however, the sympathetic tone to the heart was not changed, suggesting alterations in the sympatho-vagal balance to the heart. These findings corroborate partially with other studies that described the predominance of sympathetic activity and reduced parasympathetic action as a result of total sleep deprivation (10,16,26). Recently Tobaldini et al. (29) published an interesting study in young physicians with acute sleep deprivation associated with a night on-call. These authors showed a significantly increases in cardiac sympathetic modulation, reduction in the amplitude of cardiovascular autonomic response to gravitational stimulus associated with changes in the immune pro-inflammatory profile and increase the plasmatic levels of IFN-g (Interferon gamma) in young physicians after total sleep deprivation. In our study, we could not exclude the possibility that the sympathetic drive to other targets is increased after PSD. In fact, PSD induced an increase in sympathetic drive to the kidney (9). Direct recording of post-ganglionic sympathetic activity to different organs would improve our understanding regarding the possible topographic sympathetic changes induced by PSD. PSD group showed an increase in HR and in the incidence of cardiac arrhythmias in response to isoproterenol in comparison to the control group. It is possible that such effects induced by isoproterenol are related to the reduction of basal parasympathetic tone. It is well known that adrenergic activity may trigger cardiac arrhythmia and that vagal efferent tone is cadioprotective by opposing adrenergic actions through presynaptic inhibition of norepinephrine release and an action at the receptor level (25). Furthermore, changes in stress hormones induced by total sleep deprivation and PSD may play a role, considering that the co-occurrence of stress is an inherent factor in sleep deprivation method (11,26). Single platform methods contain one additional stress variable – isolation. However, similar results were observed in recent experiments for which we used the modified multiple platform method (30). In fact, total sleep deprivation has been
DOI: 10.3109/10641963.2014.881843
associated with alterations in the regulation of the hypothalamic-pituitary axis, which can lead to harmful physiological consequences in experimental animals (26). These data suggest that sleep-deprived animals are more susceptible to the occurrence of cardiac electrical changes when submitted to a stressful event. Sgoifo et al. (10) demonstrate that the rats deprived of sleep for 48 h showed marked response to stress, increased cardiac sympathetic nerve activity, increased activity of the hypothalamic-pituitary axis and reduced vagal activity. Although the effects on the cardiovascular system caused by sleep deprivation are still controversial, it is clear that changes in quantity or quality of sleep can affect the normal functioning of the cardiovascular system. One noticeable feature of the present investigation is the fact that this experimental models permit to isolate the effects of PSD without other comorbidities, namely, obesity, metabolic syndrome and diabetes, normally observed in the clinical situation. This possibility offers a view of how each, individually, interferes with the cardiovascular system. Thus, this study demonstrated that PSD for 1 day can modify several cardiovascular parameters and induce autonomic imbalance accompanied by impaired baroreflex sensitivity, and increased arrhythmia and tachycardia susceptibility.
Declaration of interest All authors declare no conflict of interest. F.R.A. is recipient of Capes fellowship, and C.T.B., R.R.C., M.L.A., S.T. and J.C.P. (#558924/2008-5) are recipients of CNPq fellowships.
References 1. Gangwisch JE, Heymsfield SB, Boden-Albala B, et al. Short sleep duration as a risk factor for hypertension: analyses of the first national health and nutrition examination survey. Hypertension 2006;47:833–9. 2. Gottlieb DJ, Redline S, Nieto FJ, et al. Association of usual sleep duration with hypertension: the sleep heart health study. Sleep 2006;29:1009–14. 3. Cappuccio FP, Stranges S, Kandala NB, et al. Gender-specific associations of short sleep duration with prevalent and incident hypertension: the whitehall ii study. Hypertension 2007;50: 693–700. 4. Sabanayagam C, Shankar A. Sleep duration and cardiovascular disease: results from the national health interview survey. Sleep 2010;33:1037–42. 5. Futuro-Neto HA, Coote JH. Desynchronized sleep-like pattern of sympathetic activity elicited by electrical stimulation of sites in the brainstem. Brain Res 1982;252:269–76. 6. Somers VK, Dyken ME, Mark AL, Abboud FM. Sympathetic-nerve activity during sleep in normal subjects. N Engl J Med 1993;328: 303–7. 7. Bonnet MH, Arand DL. Heart rate variability: sleep stage, time of night, and arousal influences. Electroencephalogr Clin Neurophysiol 1997;102:390–6. 8. Stein PK, Pu Y. Heart rate variability, sleep and sleep disorders. Sleep Med Rev 2012;16:47–66. 9. Perry JC, Bergamaschi CT, Campos RR, et al. Sympathetic and angiotensinergic responses mediated by paradoxical sleep loss in rats. J Renin Angiotensin Aldosterone Syst 2011;12:146–52.
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10. Sgoifo A, Buwalda B, Roos M, et al. Effects of sleep deprivation on cardiac autonomic and pituitary-adrenocortical stress reactivity in rats. Psychoneuroendocrinology 2006;31:197–208. 11. Andersen ML, Martins PJ, D’Almeida V, et al. Endocrinological and catecholaminergic alterations during sleep deprivation and recovery in male rats. J Sleep Res 2005;14:83–90. 12. Perry JC, D’Almeida V, Souza FG, et al. Consequences of subchronic and chronic exposure to intermittent hypoxia and sleep deprivation on cardiovascular risk factors in rats. Respir Physiol Neurobiol 2007;156:250–8. 13. DeMesquita S, Hale GA. Cardiopulmonary regulation after rapid-eye-movement sleep deprivation. J Appl Physiol 1992;72: 970–6. 14. Machado RB, Hipolide DC, Benedito-Silva AA, Tufik S. Sleep deprivation induced by the modified multiple platform technique: quantification of sleep loss and recovery. Brain Res 2004;1004: 45–51. 15. Machado RB, Suchecki D, Tufik S. Comparison of the sleep pattern throughout a protocol of chronic sleep restriction induced by two methods of paradoxical sleep deprivation. Brain Res Bull 2006;70: 213–20. 16. Tochikubo O, Ikeda A, Miyajima E, Ishii M. Effects of insufficient sleep on blood pressure monitored by a new multibiomedical recorder. Hypertension 1996;27:1318–24. 17. Kato M, Phillips BG, Sigurdsson G, et al. Effects of sleep deprivation on neural circulatory control. Hypertension 2000;35: 1173–5. 18. Holmes AL, Burgess HJ, Dawson D. Effects of sleep pressure on endogenous cardiac autonomic activity and body temperature. J Appl Physiol 2002;92:2578–84. 19. Sauvet F, Leftheriotis G, Gomez-Merino D, et al. Effect of acute sleep deprivation on vascular function in healthy subjects. J Appl Physiol 2010;108:68–75. 20. Carter JR, Durocher JJ, Larson RA, et al. Sympathetic neural responses to 24-hour sleep deprivation in humans: sex differences. Am J Physiol Heart Circ Physiol 2012;302:H1991–7. 21. Sayk F, Teckentrup C, Becker C, et al. Effects of selective slowwave sleep deprivation on nocturnal blood pressure dipping and daytime blood pressure regulation. Am J Physiol Regul Integr Comp Physiol 2010;298:R191–7. 22. Pagani M, Pizzinelli P, Traon AP, et al. Hemodynamic, autonomic and baroreflex changes after one night sleep deprivation in healthy volunteers. Auton Neurosci 2009;145:76–80. 23. Radulovacki M, Trbovic SM, Carley DW. Cardiopulmonary interactions following rem sleep deprivation in Sprague-Dawley rats. Exp Neurol 1997;145:371–5. 24. Matos G, Tenorio NM, Bergamaschi CT, et al. More than hormones: sex differences in cardiovascular parameters after sleep loss in rats. Prog Neuropsychopharmacol Biol Psychiatry 2013;44C:34–8. 25. Verrier RL, Tan A. Heart rate, autonomic markers, and cardiac mortality. Heart Rhythm 2009;6:S68–75. 26. Meerlo P, Sgoifo A, Suchecki D. Restricted and disrupted sleep: effects on autonomic function, neuroendocrine stress systems and stress responsivity. Sleep Med Rev 2008;12:197–210. 27. Irwin M, Thompson J, Miller C, et al. Effects of sleep and sleep deprivation on catecholamine and interleukin-2 levels in humans: clinical implications. J Clin Endocrinol Metab 1999;84: 1979–85. 28. Takase B, Akima T, Satomura K, et al. Effects of chronic sleep deprivation on autonomic activity by examining heart rate variability, plasma catecholamine, and intracellular magnesium levels. Biomed Pharmacother 2004;58:S35–9. 29. Tobaldini E, Cogliati C, Fiorelli EM, et al. One night on-call: sleep deprivation affects cardiac autonomic control and inflammation in physicians. Eur J Intern Med 2013;24:664–70. 30. Perry J, Bergamaschi C, Campos R, et al. Interconnectivity of sympathetic and sleep networks is mediated through reduction of gabaergic inhibition in the paraventricular nucleus. J Sleep Res 2013. [Epub ahead of print]. doi: 10.1111/jsr.12110.
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ORIGINAL ARTICLE
Cardiovascular function alterations induced by acute paradoxical sleep deprivation in rats F. R. Almeida1*, J. C. Perry2*, H. A. Futuro-Neto3, V. R. Almeida1, R. M. Sebastia˜o1, M. L. Andersen2, S. Tufik2, R. R. Campos1, and C. T. Bergamaschi1 1
Cardiovascular Division, Department of Physiology, Universidade Federal de Sa˜o Paulo, SP, Brazil, 2Department of Psychobiology, Universidade Federal de Sa˜o Paulo, SP, Brazil, and 3Department of Morphology, UFES, EMESCAM and Faculdade Brasileira Medical Schools, ES, Brazil
Abstract
Keywords
Sleep loss has been implicated in triggering the hypertension. The goal of the present study was investigated the possible mechanisms underlying cardiovascular alterations after acute paradoxical sleep deprivation (PSD). Male Wistar rats were assigned in two experimental groups: (1) control and (2) PSD for 24 h using the modified single platform method. Paradoxical sleep deprived rats exhibited higher blood pressure, heart rate (HR) and impaired baroreceptor sensitivity. After pharmacological autonomic double blockade (propranolol and methylatropine administration), intrinsic heart rate was decreased after PSD. The PSD rats showed a reduction in the vagal tone without affecting sympathetic tone. Isoproterenol administration (0.001, 0.01 and 1 mg/kg) induced an increase in DHR responses in PSD group. Electrocardiographic analysis in response to b-adrenergic stimulation indicated that PSD contributed to ventricular cardiac arrhythmias. Our findings suggest that acute paradoxical sleep loss induce cardiovascular alterations, autonomic imbalance accompanied by impaired baroreflex sensitivity and increased arrhythmia susceptibility.
Arrhythmia, heart rate, isoproterenol, paradoxical sleep deprivation, sleep
Introduction Recent studies have shown that either reduced or even increased total sleep time are related to increased cardiovascular risk (1–4). The different stages of sleep affect diversely the autonomic control systems leading to specific cardiovascular adjustments during sleep period (5,6). For instance, during synchronized, non-rapid eye movement sleep (NREM) period, or slow wave sleep, parasympathetic activity to cardiovascular system is predominant leading to reduction of blood pressure (BP), heart rate (HR), cardiac output and peripheral vascular resistance (6–8). Desynchronized, paradoxical or rapid eye movement (REM) period has two distinct phases: tonic and phasic. In the tonic phase, the cardiovascular parameters remain similar to NREM sleep; however, in the phasic stage of REM sleep, there is augmentation in discharges of sympathetic nervous system, linked to rapid and ephemeral increases in skeletal muscle tone. Therefore, in the REM sleep phase, BP and HR reached values similar to those observed during wakefulness (6–8). Considering that sleep deprivation does not allow the natural decline in sympathetic vasomotor tone and blood pressure during sleep, such condition is related to *These authors contributed equally to this work. Correspondence: Ca´ssia T. Bergamaschi, PhD, Cardiovascular Division, Department of Physiology, Universidade Federal de Sa˜o Paulo, Rua Botucatu, 862, CEP 04023-060, Sa˜o Paulo, SP, Brazil. Tel: +55 11 5573 7820 extn 27. Fax: +55 11 5573 7820 extn 5. E-mail: bergamaschi. [email protected]
History Received 3 October 2013 Revised 16 December 2013 Accepted 23 December 2013 Published online 27 March 2014
hyperactivity of the sympathetic nervous system related to changes in cardiovascular regulation (9) and also leading to increase of hypothalamic-pituitary–adrenocortical axis activity (10). Moreover, paradoxical sleep deprivation (PSD) increased circulating catecholamine concentrations (11), modified lipid biosynthesis (12) and increased HR (9,13) and systolic blood pressure (13). We have recently demonstrated that PSD during different periods induces an increase in sympathetic vasomotor activity, preferentially to the kidney, and such alteration was associated with differential modifications in the renin–angiotensin system components (9). However, the mechanisms underlying sympathoexcitation, tachycardia and blood pressure increase induced by PSD are not well understood; in the present study, we tested the hypothesis that changes in the reflex control of circulation by the arterial baroreceptors may play a role. Therefore, despite the fact that several studies have correlated the decrease in amount of sleep with increased cardiovascular risk (1–4), there is little information regarding the precise effects of acute PSD on cardiovascular function. Thus, the present study aimed to evaluate the effects of acute PSD for 24 h on cardiovascular function and the possible mechanisms underlying such alterations in rats.
Methods Animals Experiments were performed in 68 male adult Wistar rats (250–300 g) provided by the Centro de Desenvolvimento
568
F. R. Almeida et al.
de Modelos Experimentais para Medicina e Biologia (CEDEME) – Universidade Federal de Sa˜o Paulo. The animals were housed in groups of four in standard polypropylene cages in a room maintained at 22 C with a 12:12 h light–dark cycle (lights on at 07:00 h) and allowed free access to food and water. Rats used in this study were maintained and treated in accordance with the guidelines established by the Ethical and Practical Principles for the Use of Laboratory Animals. All animal procedures were approved by the University Ethics Committee (CEP no 2805/09). Paradoxical sleep deprivation Rats were randomly assigned to one of two experimental groups: (1) control and (2) PSD for 24 h. Two independent series of experiments were performed in control or in rats submitted to PSD. In the first series of experiments, the effects of PSD on cardiovascular function (arterial baroreceptor control of HR and autonomic balance to the heart) were assessed. In the second series of experiments, cardiovascular changes induced by isoproterenol administration (dose–response curve) were investigated. Animals were subjected to PSD for 24 h using the single platform-over-water technique. Rats were individually placed on a circular platform (6.5 cm in diameter) in a cage (23 cm 23 cm 29 cm) filled with water up to 1 cm below the platform level. During paradoxical sleep, rats tend to fall off the platform due to neck muscular atonia and awaken on contact with the water. Moreover, prior to commencement of the PSD protocol, all sleep-deprived animals received a habituation period on the platform (1 h/day for 3 days). After 24 h of PSD, the single platform procedure was effective in producing a total suppression of paradoxical sleep and a reduction in slow wave sleep (34–39%) in rats (14,15). Food and water were provided ad libitum. The control groups were housed in similar individual cages containing bedding and one platform without water. The rats were kept in the same room as the experimental rats during the study. First series of experiments Analysis of cardiovascular function and the control of heart rate by the arterial baroreceptors in conscious rats Immediately after PSD rats were anesthetized with halothane (2% in 100% oxygen-enriched air – during 20 min) and instrumented with femoral venous and arterial catheters for drug injection and arterial pressure recording, respectively. Catheters were externalized through the neck. Cardiovascular measurements were made 4–5 h later and lasted for 20 min. During this period, sleep deprivation was carried out by gentle handling, which involved tapping the cages whenever the animals appeared drowsy. MAP and HR were recorded in conscious rats via the arterial catheter, connected to a pressure transducer and to an analogical digital converter (PowerLab, AD Instruments, Bella Vista, NSW, Australia). Mean arterial pressure (MAP) and HR signals on conscious rats were derived from pulsatile arterial pressure. For arterial baroreceptor reflex function analysis, pressor doses of phenylephrine (3, 5 and 10 mg/kg, IV – Sigma-Aldrich, St. Louis, MO) and depressor dose of sodium nitroprusside (5, 15 and
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20 mg IV Sigma-Aldrich, St. Louis, MO) were randomly acutely administered in an interval of 15 min to induce progressive increase or decrease of blood pressure and the reflex bradycardia or tachycardia, respectively. The sensitivity of the arterial baroreceptor for HR control was evaluated by the mean index relating changes in HR to changes in MAP and was expressed as beats per mmHg (bpm/mmHg). Values of matching MAP variations with reflex HR responses were plotted separately for each vasoactive drug to create linear regression curves of baroreceptor function for each group, and their slopes were compared to evaluate changes in baroreflex gain. All signals were recorded on a computer-based data acquisition system (PowerLab system, AD Instruments, Bella Vista, NSW, Australia) with a 2-kHz sampling rate. Intrinsic heart rate and autonomic modulation Sympathetic and vagal tones were assessed by autonomic blockade produced by acute injection of propanolol (4 mg/kg; IV – Sigma-Aldrich, St. Louis, MO) and methylatropine (3 mg/kg; IV – Sigma-Aldrich, St. Louis, MO), respectively. The difference between HR calculated at the end of 15 min after the propanolol administration and the basal HR was considered as the sympathetic tone. On the other hand, the difference between the HR calculated at the end of 15 min after methylatropine administration and the basal HR was considered as the vagal tone. The intrinsic heart rate was assessed after dual pharmacological blockade by propanolol and methylatropine. Second series of experiments Isoproterenol dose–response curve Rats were anesthetized with halothane (2% in 100% oxygenenriched air) and instrumented with femoral venous and arterial catheters for drug injection and arterial pressure recording, respectively. For electrocardiogram analysis, two silver electrodes were implanted in the left and in the right side of thorax between the 5th and 6th intercostals space, respectively, externalized through the neck and connected to an AC amplifier (Neuro Log, Digitimer Ltd, Hertfordshire, UK) and a band-pass filter (50–1000 Hz, 2 K sampling rate). All signals were recorded on a computer-based data acquisition system (PowerLab system, AD Instruments, Bella Vista, NSW, Australia). Isoproterenol (Sigma-Aldrich, St. Louis, MO) was injected IV at doses of 0.001, 0.01 and 1 mg/kg. The maximum HR response was observed as well as the total numbers of cardiac arrhythmias (defined as extrabeats followed by a compensatory pause) measured for 10 min after isoproterenol administration in conscious rats. Statistical analyses Student’s t-test for independent samples by group was used to analyze the data. Values are expressed as mean ± SEM. p50.05 was considered statistically significant.
Results Figure 1(A) and (B), respectively, shows that PSD for 24 h resulted in significant increased MAP (C 108 ± 1, n ¼ 12; PSD 123 ± 3 mmHg, n ¼ 12, p50.001) and HR (C 337 ± 6,
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Figure 2. (A) Cardiac baroreflex function and the respective slope values correlating mean arterial pressure decrease (DMAP) and the reflex heart rate increase (DHR) induced by sodium nitroprusside (5–20 mg/kg, IV). (B) Cardiac baroreflex function and the respective slope values correlating mean arterial pressure increase (DMAP) and the reflex heart rate decrease (DHR) induced by phenylephrine (3–10 mg/kg, IV). *p50.05 compared to control group (Student’s t-test). C (control/ n ¼ 10); PSD (paradoxical sleep deprivation/n ¼ 12).
and (B), respectively. The PSD group displayed significantly impaired sensitivity of the arterial baroreceptor control of HR for both the depressor and pressor responses. In the second and independent series of experiments, the HR responses to isoproterenol administration were evaluated (0.001, 0.01, 1 mg/kg; Figure 3A). The three progressive doses of isoproterenol induced statistically significant increase in DHR responses in PSD group (87 ± 12; 142 ± 9; 201 ± 8 bpm, p50.05) compared to control group (48 ± 8; 83 ± 16; 138 ± 10 bpm), respectively. Finally, the electrocardiographic analysis demonstrated that the PSD group showed a significant increase in the total number of ventricular cardiac arrhythmias compared to control group after the administration of isoproterenol at doses of 0.001 mg/kg (control 0.83 ± 0.5 and PSD 3.33 ± 1.0 extra beats/10 min) and 1 mg/ kg (control 2.8 ± 2.4 and PSD 10.5 ± 1.7 extra beats/10 min) (Figure 3B). However, no significant difference was found between groups in the intermediate dose (0.01 mg/kg; c: 3.67 ± 2.38 and PSD: 6.0 ± 2.03 extra beats/10 min). Figure 1. Effects of acute paradoxical sleep deprivation on mean arterial pressure (Panel A), heart rate (Panel B) and intrinsic heart rate (Panel C) in rats. *p50.05 compared to control group (Student’s t-test). Data are expressed as mean ± SEM. C (control/n ¼ 12); PSD (paradoxical sleep deprivation/n ¼ 12).
n ¼ 12; PSD 386 ± 5 bpm, n ¼ 12, p50.001) compared to control group. Furthermore, after pharmacological autonomic double blockade with propranolol and methylatropine administration, paradoxical sleep-deprived rats showed a significant reduction in intrinsic heart rate compared to control group (C 420 ± 10, n ¼ 10; PSD 387 ± 6 bpm, n ¼ 12, p50.001; Figure 1C). The PSD group showed a significantly lower vagal tone compared to control group (C 132 ± 15, n ¼ 10 and PSD 61 ± 11 bpm, n ¼ 12; p50.05). However, no significant difference was observed in sympathetic tone (C 34 ± 5, n ¼ 10 and PSD 53 ± 13 bpm, n ¼ 12). The HR baroreceptor reflex functions and the slope values for depressor and pressor responses are shown in Figure 2(A)
Discussion The results of the present study provide evidence that 24 h of PSD can affect cardiovascular function in male Wistar rats. Specifically, acute PSD induced an increase of HR and BP associated with an impairment of the baroreflex control of blood pressure. The PSD rats showed a reduction in the vagal tone and intrinsic heart rate. Finally, the acute PSD leads to an increase cardiovascular sensitivity to b-adrenergic stimulation, and a significant increase in the incidence of ventricular cardiac arrhythmias induced by isoproterenol. Altogether such changes are important mechanisms triggering increased cardiovascular risk induced by PSD. Heart rate and BP were significantly increased in animals submitted to total sleep deprivation and PSD (9,10,13). Other studies showed that deprivation and fragmentation of sleep also generates increases in baseline hemodynamic parameters in humans (16–20). Sauvet et al. (19) observed an increase
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Figure 3. (A) Effects of increasing doses of isoproterenol (0.001, 0.01 and 1 mg/kg, IV) on heart rate (delta) and (B) total number of arrhythmias (arrhythmias/10 min). *p50.05 compared to control group (Student’s t-test). Data are expressed as mean ± SEM. C (control/n ¼ 10); PSD (paradoxical sleep deprivation/n ¼ 12).
in blood pressure only after a period of 36 h of total sleep deprivation, while Kato et al. (17) found an increase in blood pressure without an effect on HR, after 24 h of total sleep deprivation. Moreover, a decrease in HR after 30 h of total sleep deprivation was also reported (18). In humans, the discrepancies between the results in various studies can be at least partially explained by the study conditions, variations in the studies in relation to age, gender and other comorbidities, that may have influence on cardiovascular parameters. However, animal experimentation allows for the assessment of the isolated effects of PSD. Given that a significant impairment of baroreceptor sensitivity was induced in PSD, the effects of sleep on baroreflex response may be relevant to our understanding regarding a major mechanism that triggers increase in sympathetic activity, blood pressure and HR. Changes in sensitivity of the baroreflex response may be considered as an important prognostic marker of impaired functioning of the cardiovascular system. The results of this study demonstrated that paradoxical sleep deprived rats showed altered cardiac baroreflex sensitivity. Studies addressing these issues have provided contrasting results. Sayk et al. (21) and Pagani et al. (22) showed no alteration of baroreflex control after total sleep deprivation in humans. However, Radulovacki et al. (23) demonstrated that rats deprived of
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paradoxical sleep for 48 h showed an increase in baroreflex sensitivity while Matos et al. (24), observed a reduction in the same parameter. These discrepancies might be in part explained by the fact that most of the studies used different experimental protocols of sleep deprivation in terms of number of hours of sleep loss, study design, experimental settings and population characteristics. Intrinsic heart rate is lower in the PSD group compared to control group. Although the present study did not directly evaluate the mechanisms involved in the generation of pacemaker frequency, we could suggest that the PSD is capable of interfering with these mechanisms by modifying the firing frequency of the sinoatrial node. One hypothesis that explains the alterations after sleep deprivation is the incidence of abnormalities in the gradients of ionic currents, involved in transmembrane depolarization and repolarization of the sinoatrial node (25). Several studies have shown that total sleep deprivation and PSD is associated with sympathetic hyperactivity (9,10,26) and increased circulating catecholamines (11,27,28). In the present study, we assessed the cardiac autonomic balance through double pharmacological autonomic blockade. These results showed that vagal tone was lower after PSD, however, the sympathetic tone to the heart was not changed, suggesting alterations in the sympatho-vagal balance to the heart. These findings corroborate partially with other studies that described the predominance of sympathetic activity and reduced parasympathetic action as a result of total sleep deprivation (10,16,26). Recently Tobaldini et al. (29) published an interesting study in young physicians with acute sleep deprivation associated with a night on-call. These authors showed a significantly increases in cardiac sympathetic modulation, reduction in the amplitude of cardiovascular autonomic response to gravitational stimulus associated with changes in the immune pro-inflammatory profile and increase the plasmatic levels of IFN-g (Interferon gamma) in young physicians after total sleep deprivation. In our study, we could not exclude the possibility that the sympathetic drive to other targets is increased after PSD. In fact, PSD induced an increase in sympathetic drive to the kidney (9). Direct recording of post-ganglionic sympathetic activity to different organs would improve our understanding regarding the possible topographic sympathetic changes induced by PSD. PSD group showed an increase in HR and in the incidence of cardiac arrhythmias in response to isoproterenol in comparison to the control group. It is possible that such effects induced by isoproterenol are related to the reduction of basal parasympathetic tone. It is well known that adrenergic activity may trigger cardiac arrhythmia and that vagal efferent tone is cadioprotective by opposing adrenergic actions through presynaptic inhibition of norepinephrine release and an action at the receptor level (25). Furthermore, changes in stress hormones induced by total sleep deprivation and PSD may play a role, considering that the co-occurrence of stress is an inherent factor in sleep deprivation method (11,26). Single platform methods contain one additional stress variable – isolation. However, similar results were observed in recent experiments for which we used the modified multiple platform method (30). In fact, total sleep deprivation has been
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associated with alterations in the regulation of the hypothalamic-pituitary axis, which can lead to harmful physiological consequences in experimental animals (26). These data suggest that sleep-deprived animals are more susceptible to the occurrence of cardiac electrical changes when submitted to a stressful event. Sgoifo et al. (10) demonstrate that the rats deprived of sleep for 48 h showed marked response to stress, increased cardiac sympathetic nerve activity, increased activity of the hypothalamic-pituitary axis and reduced vagal activity. Although the effects on the cardiovascular system caused by sleep deprivation are still controversial, it is clear that changes in quantity or quality of sleep can affect the normal functioning of the cardiovascular system. One noticeable feature of the present investigation is the fact that this experimental models permit to isolate the effects of PSD without other comorbidities, namely, obesity, metabolic syndrome and diabetes, normally observed in the clinical situation. This possibility offers a view of how each, individually, interferes with the cardiovascular system. Thus, this study demonstrated that PSD for 1 day can modify several cardiovascular parameters and induce autonomic imbalance accompanied by impaired baroreflex sensitivity, and increased arrhythmia and tachycardia susceptibility.
Declaration of interest All authors declare no conflict of interest. F.R.A. is recipient of Capes fellowship, and C.T.B., R.R.C., M.L.A., S.T. and J.C.P. (#558924/2008-5) are recipients of CNPq fellowships.
References 1. Gangwisch JE, Heymsfield SB, Boden-Albala B, et al. Short sleep duration as a risk factor for hypertension: analyses of the first national health and nutrition examination survey. Hypertension 2006;47:833–9. 2. Gottlieb DJ, Redline S, Nieto FJ, et al. Association of usual sleep duration with hypertension: the sleep heart health study. Sleep 2006;29:1009–14. 3. Cappuccio FP, Stranges S, Kandala NB, et al. Gender-specific associations of short sleep duration with prevalent and incident hypertension: the whitehall ii study. Hypertension 2007;50: 693–700. 4. Sabanayagam C, Shankar A. Sleep duration and cardiovascular disease: results from the national health interview survey. Sleep 2010;33:1037–42. 5. Futuro-Neto HA, Coote JH. Desynchronized sleep-like pattern of sympathetic activity elicited by electrical stimulation of sites in the brainstem. Brain Res 1982;252:269–76. 6. Somers VK, Dyken ME, Mark AL, Abboud FM. Sympathetic-nerve activity during sleep in normal subjects. N Engl J Med 1993;328: 303–7. 7. Bonnet MH, Arand DL. Heart rate variability: sleep stage, time of night, and arousal influences. Electroencephalogr Clin Neurophysiol 1997;102:390–6. 8. Stein PK, Pu Y. Heart rate variability, sleep and sleep disorders. Sleep Med Rev 2012;16:47–66. 9. Perry JC, Bergamaschi CT, Campos RR, et al. Sympathetic and angiotensinergic responses mediated by paradoxical sleep loss in rats. J Renin Angiotensin Aldosterone Syst 2011;12:146–52.
Effects of acute paradoxical sleep deprivation
571
10. Sgoifo A, Buwalda B, Roos M, et al. Effects of sleep deprivation on cardiac autonomic and pituitary-adrenocortical stress reactivity in rats. Psychoneuroendocrinology 2006;31:197–208. 11. Andersen ML, Martins PJ, D’Almeida V, et al. Endocrinological and catecholaminergic alterations during sleep deprivation and recovery in male rats. J Sleep Res 2005;14:83–90. 12. Perry JC, D’Almeida V, Souza FG, et al. Consequences of subchronic and chronic exposure to intermittent hypoxia and sleep deprivation on cardiovascular risk factors in rats. Respir Physiol Neurobiol 2007;156:250–8. 13. DeMesquita S, Hale GA. Cardiopulmonary regulation after rapid-eye-movement sleep deprivation. J Appl Physiol 1992;72: 970–6. 14. Machado RB, Hipolide DC, Benedito-Silva AA, Tufik S. Sleep deprivation induced by the modified multiple platform technique: quantification of sleep loss and recovery. Brain Res 2004;1004: 45–51. 15. Machado RB, Suchecki D, Tufik S. Comparison of the sleep pattern throughout a protocol of chronic sleep restriction induced by two methods of paradoxical sleep deprivation. Brain Res Bull 2006;70: 213–20. 16. Tochikubo O, Ikeda A, Miyajima E, Ishii M. Effects of insufficient sleep on blood pressure monitored by a new multibiomedical recorder. Hypertension 1996;27:1318–24. 17. Kato M, Phillips BG, Sigurdsson G, et al. Effects of sleep deprivation on neural circulatory control. Hypertension 2000;35: 1173–5. 18. Holmes AL, Burgess HJ, Dawson D. Effects of sleep pressure on endogenous cardiac autonomic activity and body temperature. J Appl Physiol 2002;92:2578–84. 19. Sauvet F, Leftheriotis G, Gomez-Merino D, et al. Effect of acute sleep deprivation on vascular function in healthy subjects. J Appl Physiol 2010;108:68–75. 20. Carter JR, Durocher JJ, Larson RA, et al. Sympathetic neural responses to 24-hour sleep deprivation in humans: sex differences. Am J Physiol Heart Circ Physiol 2012;302:H1991–7. 21. Sayk F, Teckentrup C, Becker C, et al. Effects of selective slowwave sleep deprivation on nocturnal blood pressure dipping and daytime blood pressure regulation. Am J Physiol Regul Integr Comp Physiol 2010;298:R191–7. 22. Pagani M, Pizzinelli P, Traon AP, et al. Hemodynamic, autonomic and baroreflex changes after one night sleep deprivation in healthy volunteers. Auton Neurosci 2009;145:76–80. 23. Radulovacki M, Trbovic SM, Carley DW. Cardiopulmonary interactions following rem sleep deprivation in Sprague-Dawley rats. Exp Neurol 1997;145:371–5. 24. Matos G, Tenorio NM, Bergamaschi CT, et al. More than hormones: sex differences in cardiovascular parameters after sleep loss in rats. Prog Neuropsychopharmacol Biol Psychiatry 2013;44C:34–8. 25. Verrier RL, Tan A. Heart rate, autonomic markers, and cardiac mortality. Heart Rhythm 2009;6:S68–75. 26. Meerlo P, Sgoifo A, Suchecki D. Restricted and disrupted sleep: effects on autonomic function, neuroendocrine stress systems and stress responsivity. Sleep Med Rev 2008;12:197–210. 27. Irwin M, Thompson J, Miller C, et al. Effects of sleep and sleep deprivation on catecholamine and interleukin-2 levels in humans: clinical implications. J Clin Endocrinol Metab 1999;84: 1979–85. 28. Takase B, Akima T, Satomura K, et al. Effects of chronic sleep deprivation on autonomic activity by examining heart rate variability, plasma catecholamine, and intracellular magnesium levels. Biomed Pharmacother 2004;58:S35–9. 29. Tobaldini E, Cogliati C, Fiorelli EM, et al. One night on-call: sleep deprivation affects cardiac autonomic control and inflammation in physicians. Eur J Intern Med 2013;24:664–70. 30. Perry J, Bergamaschi C, Campos R, et al. Interconnectivity of sympathetic and sleep networks is mediated through reduction of gabaergic inhibition in the paraventricular nucleus. J Sleep Res 2013. [Epub ahead of print]. doi: 10.1111/jsr.12110.
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