Clinical and Experimental Pharmacology and Physiology (1992) 19,48 1-488
A COMPARISON OF GUANFACINE, BUNAZOSIN, ATENOLOL AND NADOLOL ON BLOOD PRESSURE AND PLASMA NORADRENALINE RESPONSES TO COLD PRESSOR TESTING Masatoshi Koshiji, Hiroyasu Ito, Shinya Minatoguchi, Hiroko Watanabe, Yoko Imai, Masao Kakami and Senri Hirakawa The Second Department of Internal Medicine, Gifu University School of Medicine, Gfu, Japan (Received 10 September 1991; revision received 6 January 1992)
SUMMARY 1. The role of the presynaptic adrenoceptor subtypes in man was investigated based on observation of the changes in blood pressure (ABP) and plasma noradrenaline concentration (ANA) with the cold pressor test (CPT). 2. The CPT was well reproducible for BP and NA when performed at a 2 week interval in patients with mild hypertension. 3. After administration for 4 weeks, guanfacine (Gf; a*-adrenoceptor agonist) decreased the ANA response to CPT. 4. After administration for 2 or 4 weeks, bunazosin (Bu; a,-adrenoceptor antagonist) atenolol (At; Pi-adrenoceptor antagonist) and nadolol (Nd; non-selective P-adrenoceptor antagonist) did not affect the ANA response to CPT. 5. Both Gf and Bu decreased the systolic blood pressure response (ASBP) to CPT after 4 weeks of the administration. Neither At nor Nd significantly changed the ASBP response to CPT. 6 . It is likely that Gf stimulated the presynaptic (YZ adrenoceptors at the sympathetic nerve endings as well as the central a2 adrenoceptors, inhibiting the release of noradrenaline. It is unlikely that Bu, At and Nd exerted any clearly defined action on the presynaptic adrenoceptors in human hypertensive subjects. Key words: antihypertensive drug, cold pressor test, plasma noradrenaline.
INTRODUCTION Adrenoceptor subtypes, such as a ~ (YZ, , PI and Pz, have been characterized at sympathetic nerve endings. In vitro studies have demonstrated that presynaptic ( Y I - and az-adrenoceptors inhibit stimulation-induced noradrenaline release (Langer 1981; Hicks et al. 1986; Murphy et al. 1989), while 01-and &-adrenoceptors enhance stimulation-induced release of noradrenaline (Stjarne & Brundin 1976; Langer 1981; Ueda et al.
1985). However, presynaptic LYI-, PI- and Pa-adrenoceptors have not been shown to have a primary role in modulating noradrenaline (NA) reIease from sympathetic nerve endings, while presynaptic apadrenoceptors have been shown, in vivo, to play a crucial role in regulating NA release (Stevens et a f . 1982; Steenberg et al. 1983; Uchida et al. 1984). In humans, however, it is still unclear to what extent the pre-
Cotrespondence: M. Koshiji, The Second Department of Internal Medicine, Gifu University School of Medicine, 40Tsukasa-Machi, Gifu, Japan.
482
M. Koshiji et al.
synaptic adrenoceptors participate in regulating NA release from the sympathetic nerve endings. The present study was designed to clarify the role of presynaptic adrenoceptor subtypes in modulating the release of NA from sympathetic nerve endings in patients with mild essential hypertension. NA release was measured with an attempt to stimulate the sympathetic nervous system (i.e. by means of the cold pressor test).
METHODS All subjects gave informed consent to enter the following studies.
Reproducibility of the cold pressor test The cold pressor test (CPT) was performed twice at intervals of 2 weeks in patients with mild essential hypertension in order to investigateits reproducibility. Mild essential hypertension was defined as diastolic blood pressure in the sitting position of between 90 and 104 mmHg on at least three blood pressure readings obtained at 2 week intervals (Table 1).
measurements and CPT were performed on the day before, 2 weeks and 4 weeks after the start of the administration of drugs.
Procedures for CPT The patient lay quietly in the supine position, and a 19 gauge needle composing an arm of three-way needle set was inserted into an antecubital vein. The point of time at which the instrumentations were completed was defined as 0 min, and physiological saline was then infused at a low volume through the needle. After 30 min, CPT was performed by immersing one of the subject's hands into 4OC iced water for precisely 1 min.
Measurements of plasma catecholamine concentration and blood pressure Blood samples (7 mL each) were obtained, within 10-15 s, at the points of time shown in the time schedule (Fig. 1). Plasma NA and adrenaline (A) concentrations were measured by means of high performance liquid chromatography (Shimadzu, Japan; LC-6A, Zorvax SCX-300, RF-5OOLCA) coupled with the trihydroxy indole method. Blood pressure and
The administration of antihypertensive drugs Half a milligram of an az-agonist, guanfacine (Sorkin & Heel 1986), was administered at bedtime to the first group of 10 subjects. The second group of 10 subjects
received an a,-antagonist, bunazosin (Suzuki et al. 1987), at a dose of 0.5 mg t.i.d. Fifty milligrams of a &antagonist, atenolol (Frishman & Teicher 1985), was administered once a day in the morning to the third group of 10 subjects. The fourth group of 10 subjects received 30 mg of the non-selective B-adrenoceptor antagonist, nadolol (Frishman & Teicher 1985), once a day in the morning. All subjects had mild essential hypertension. There were no differences in age or systolic and diastolic blood pressure between the four medication groups (Table 1). Blood pressure
I
I
Blood sampling
I
0
25
20
35
"4
C PT
Time immediately after Instrumentation (min)
Fig. 1. Schedule of the CPT and blood sampling. At time points 1-6, blood samples were taken for the measurements of plasma catecholamine concentrations.
Table 1. Subjects employed for studying CPT reproducibility and those allocated to four medication groups
Hypertensives Reproducibility (2 week interval) Guanfacine (a*-agonist) Bunazosin (CY,-antagonist) Atenolol (fi~-antagonist) Nadolol Pz-antagonist)
Age (years)*
SBP
DBP (mmHg)t
52.5f8.6 49.8 f 10.4 50.6 f7.9 46.7f 11.1 51.2f 10.5
149.8 f 3.4 149.4f 1.6 149.0 f3.6 153.8f4.9 156.2f 4.8
94.6 f0.6 94.6 f1.0 96.2f 1.3 96.0 f 1.4 97.0 f 2.3
SBP, systolic blood pressure; DBP, diastolic blood pressure. Blood pressure was measured in the sitting position in outpatient clinic before the first cold pressor test. *Data are expressed as mean fs.e.m. tData are expressed as mean f s.e.m. n = 10.
Antihypertensive drugs and catecholamines pulse rate were measured at 1 min intervals with an automatic sphygmomanometer (BP-203; Nippon Colin, Japan) in the contralateral arm throughout the experiment. The values of plasma CA concentration, blood pressure and pulse rate at time point prior to the CPT (point 3, Fig. 1) were taken to be the values before CPT, and the highest later value (points 4 or 5 , Fig. 1) as the value after CPT. The differences in plasma CA concentration, blood pressure and pulse rate before and after the CPT were attributed to CPT. In the laboratory, 2 mL of the human plasma was divided into halves and 1 ng of standard NA and 1 ng of standard A (Sigma, St Louis, MO, USA; NA; A7256; A, E-4375)was added into one of the samples. The differences in NA and A between the plasma with standard NA and A and the plasma without were measured. The values of the differences obtained from 20 normal subjects were 1.018+0.067 ng/mL (mean fs.e.m.) for NA and 0.985 f0.062 ng/ mL for A (Ishimura et al. 1988). Blood pressures were measured in the outpatient clinic using a mercury sphygmomanometer.
Statistical analysis All the values obtained are expressed as mean fs.e.m. lntra-individual comparisons were performed for reproducibility by linear regression analysis. Significant differences between three groups were analysed by one-way analysis of variance. Significant differences between more than three groups of variables in one and the same patients were assessed by two-way
483
analysis of variance with repeated measures followed by the Bonferroni method. P values less than 0.05 were considered to be statistically significant.
RESULTS Reproducibility of CPT Table 2 shows the haemodynamic parameters and plasma CA concentrations before and following the CPT that was performed at a 2 week interval in patients with mild hypertension. There was a good correlation between the first and the second measurements of systolic blood pressure (SBP), diastolic blood pressure (DBP), NA and A.
Changes in blood pressure and pulse rate produced by antihypertensive drugs Figure 2 shows the time course changes in blood pressure and pulse rate (PR) measured before and after the start of the administration of the antihypertensive drugs. Measurements were made at 2 week intervals, starting 4 weeks before ( - 4 weeks) and continuing until the end of 4 weeks after the start of the administration of the antihypertensive drugs. As compared with the control values (0 week), the pblockers atenolol (At) and nadalol (Nd) decreased P R significantly, but bunazosin (Bu) and guanfacine (Gf) did not. Systolic blood pressure and DBP were decreased by all drugs to the same extent (i.e. per cent
Table 2. Reproducibility of the responses of pulse rate, blood pressure and plasma catecholamine concentration to CPT at a 2-week interval in hypertensives
First measurement Pulse rate (beats/min) before CPT after CPT Systolic blood pressure (mmHg) before CPT after CPT Diastolic blood pressure (mmHg) before CPT after CPT Noradrenaline (ng/ mL) before CPT after CPT Adrenaline (ng/ mL) before CPT after CPT
Second measurement
Correlation coefficient (r)
69.9 f 1.6 69.2+ 2.5
0.091 0.797*
(32.3 4.8 145.4 f5.1
132.9 f5.4 148.0 iz 5.4
0.874** 0.842**
73.5f2.9 8 1.3 f3.3
75.9 f3.0 84.1 f3.0
D.906**
0.247 f0.020 0.328 f0.024
0.230 f0.028 0.326 f0.036
0.882** 0.693*
0.095 f0.027 0.114f0.028
0.084 f0.023 0.098 f0.026
0.830** 0.862**
71.5f 1.9 71.6
+ 2.4
*
0.843* *
Correlation coefficients were obtained between the first and second measurements. Data are expressed as mean fs.e.m.
*P
A COMPARISON OF GUANFACINE, BUNAZOSIN, ATENOLOL AND NADOLOL ON BLOOD PRESSURE AND PLASMA NORADRENALINE RESPONSES TO COLD PRESSOR TESTING Masatoshi Koshiji, Hiroyasu Ito, Shinya Minatoguchi, Hiroko Watanabe, Yoko Imai, Masao Kakami and Senri Hirakawa The Second Department of Internal Medicine, Gifu University School of Medicine, Gfu, Japan (Received 10 September 1991; revision received 6 January 1992)
SUMMARY 1. The role of the presynaptic adrenoceptor subtypes in man was investigated based on observation of the changes in blood pressure (ABP) and plasma noradrenaline concentration (ANA) with the cold pressor test (CPT). 2. The CPT was well reproducible for BP and NA when performed at a 2 week interval in patients with mild hypertension. 3. After administration for 4 weeks, guanfacine (Gf; a*-adrenoceptor agonist) decreased the ANA response to CPT. 4. After administration for 2 or 4 weeks, bunazosin (Bu; a,-adrenoceptor antagonist) atenolol (At; Pi-adrenoceptor antagonist) and nadolol (Nd; non-selective P-adrenoceptor antagonist) did not affect the ANA response to CPT. 5. Both Gf and Bu decreased the systolic blood pressure response (ASBP) to CPT after 4 weeks of the administration. Neither At nor Nd significantly changed the ASBP response to CPT. 6 . It is likely that Gf stimulated the presynaptic (YZ adrenoceptors at the sympathetic nerve endings as well as the central a2 adrenoceptors, inhibiting the release of noradrenaline. It is unlikely that Bu, At and Nd exerted any clearly defined action on the presynaptic adrenoceptors in human hypertensive subjects. Key words: antihypertensive drug, cold pressor test, plasma noradrenaline.
INTRODUCTION Adrenoceptor subtypes, such as a ~ (YZ, , PI and Pz, have been characterized at sympathetic nerve endings. In vitro studies have demonstrated that presynaptic ( Y I - and az-adrenoceptors inhibit stimulation-induced noradrenaline release (Langer 1981; Hicks et al. 1986; Murphy et al. 1989), while 01-and &-adrenoceptors enhance stimulation-induced release of noradrenaline (Stjarne & Brundin 1976; Langer 1981; Ueda et al.
1985). However, presynaptic LYI-, PI- and Pa-adrenoceptors have not been shown to have a primary role in modulating noradrenaline (NA) reIease from sympathetic nerve endings, while presynaptic apadrenoceptors have been shown, in vivo, to play a crucial role in regulating NA release (Stevens et a f . 1982; Steenberg et al. 1983; Uchida et al. 1984). In humans, however, it is still unclear to what extent the pre-
Cotrespondence: M. Koshiji, The Second Department of Internal Medicine, Gifu University School of Medicine, 40Tsukasa-Machi, Gifu, Japan.
482
M. Koshiji et al.
synaptic adrenoceptors participate in regulating NA release from the sympathetic nerve endings. The present study was designed to clarify the role of presynaptic adrenoceptor subtypes in modulating the release of NA from sympathetic nerve endings in patients with mild essential hypertension. NA release was measured with an attempt to stimulate the sympathetic nervous system (i.e. by means of the cold pressor test).
METHODS All subjects gave informed consent to enter the following studies.
Reproducibility of the cold pressor test The cold pressor test (CPT) was performed twice at intervals of 2 weeks in patients with mild essential hypertension in order to investigateits reproducibility. Mild essential hypertension was defined as diastolic blood pressure in the sitting position of between 90 and 104 mmHg on at least three blood pressure readings obtained at 2 week intervals (Table 1).
measurements and CPT were performed on the day before, 2 weeks and 4 weeks after the start of the administration of drugs.
Procedures for CPT The patient lay quietly in the supine position, and a 19 gauge needle composing an arm of three-way needle set was inserted into an antecubital vein. The point of time at which the instrumentations were completed was defined as 0 min, and physiological saline was then infused at a low volume through the needle. After 30 min, CPT was performed by immersing one of the subject's hands into 4OC iced water for precisely 1 min.
Measurements of plasma catecholamine concentration and blood pressure Blood samples (7 mL each) were obtained, within 10-15 s, at the points of time shown in the time schedule (Fig. 1). Plasma NA and adrenaline (A) concentrations were measured by means of high performance liquid chromatography (Shimadzu, Japan; LC-6A, Zorvax SCX-300, RF-5OOLCA) coupled with the trihydroxy indole method. Blood pressure and
The administration of antihypertensive drugs Half a milligram of an az-agonist, guanfacine (Sorkin & Heel 1986), was administered at bedtime to the first group of 10 subjects. The second group of 10 subjects
received an a,-antagonist, bunazosin (Suzuki et al. 1987), at a dose of 0.5 mg t.i.d. Fifty milligrams of a &antagonist, atenolol (Frishman & Teicher 1985), was administered once a day in the morning to the third group of 10 subjects. The fourth group of 10 subjects received 30 mg of the non-selective B-adrenoceptor antagonist, nadolol (Frishman & Teicher 1985), once a day in the morning. All subjects had mild essential hypertension. There were no differences in age or systolic and diastolic blood pressure between the four medication groups (Table 1). Blood pressure
I
I
Blood sampling
I
0
25
20
35
"4
C PT
Time immediately after Instrumentation (min)
Fig. 1. Schedule of the CPT and blood sampling. At time points 1-6, blood samples were taken for the measurements of plasma catecholamine concentrations.
Table 1. Subjects employed for studying CPT reproducibility and those allocated to four medication groups
Hypertensives Reproducibility (2 week interval) Guanfacine (a*-agonist) Bunazosin (CY,-antagonist) Atenolol (fi~-antagonist) Nadolol Pz-antagonist)
Age (years)*
SBP
DBP (mmHg)t
52.5f8.6 49.8 f 10.4 50.6 f7.9 46.7f 11.1 51.2f 10.5
149.8 f 3.4 149.4f 1.6 149.0 f3.6 153.8f4.9 156.2f 4.8
94.6 f0.6 94.6 f1.0 96.2f 1.3 96.0 f 1.4 97.0 f 2.3
SBP, systolic blood pressure; DBP, diastolic blood pressure. Blood pressure was measured in the sitting position in outpatient clinic before the first cold pressor test. *Data are expressed as mean fs.e.m. tData are expressed as mean f s.e.m. n = 10.
Antihypertensive drugs and catecholamines pulse rate were measured at 1 min intervals with an automatic sphygmomanometer (BP-203; Nippon Colin, Japan) in the contralateral arm throughout the experiment. The values of plasma CA concentration, blood pressure and pulse rate at time point prior to the CPT (point 3, Fig. 1) were taken to be the values before CPT, and the highest later value (points 4 or 5 , Fig. 1) as the value after CPT. The differences in plasma CA concentration, blood pressure and pulse rate before and after the CPT were attributed to CPT. In the laboratory, 2 mL of the human plasma was divided into halves and 1 ng of standard NA and 1 ng of standard A (Sigma, St Louis, MO, USA; NA; A7256; A, E-4375)was added into one of the samples. The differences in NA and A between the plasma with standard NA and A and the plasma without were measured. The values of the differences obtained from 20 normal subjects were 1.018+0.067 ng/mL (mean fs.e.m.) for NA and 0.985 f0.062 ng/ mL for A (Ishimura et al. 1988). Blood pressures were measured in the outpatient clinic using a mercury sphygmomanometer.
Statistical analysis All the values obtained are expressed as mean fs.e.m. lntra-individual comparisons were performed for reproducibility by linear regression analysis. Significant differences between three groups were analysed by one-way analysis of variance. Significant differences between more than three groups of variables in one and the same patients were assessed by two-way
483
analysis of variance with repeated measures followed by the Bonferroni method. P values less than 0.05 were considered to be statistically significant.
RESULTS Reproducibility of CPT Table 2 shows the haemodynamic parameters and plasma CA concentrations before and following the CPT that was performed at a 2 week interval in patients with mild hypertension. There was a good correlation between the first and the second measurements of systolic blood pressure (SBP), diastolic blood pressure (DBP), NA and A.
Changes in blood pressure and pulse rate produced by antihypertensive drugs Figure 2 shows the time course changes in blood pressure and pulse rate (PR) measured before and after the start of the administration of the antihypertensive drugs. Measurements were made at 2 week intervals, starting 4 weeks before ( - 4 weeks) and continuing until the end of 4 weeks after the start of the administration of the antihypertensive drugs. As compared with the control values (0 week), the pblockers atenolol (At) and nadalol (Nd) decreased P R significantly, but bunazosin (Bu) and guanfacine (Gf) did not. Systolic blood pressure and DBP were decreased by all drugs to the same extent (i.e. per cent
Table 2. Reproducibility of the responses of pulse rate, blood pressure and plasma catecholamine concentration to CPT at a 2-week interval in hypertensives
First measurement Pulse rate (beats/min) before CPT after CPT Systolic blood pressure (mmHg) before CPT after CPT Diastolic blood pressure (mmHg) before CPT after CPT Noradrenaline (ng/ mL) before CPT after CPT Adrenaline (ng/ mL) before CPT after CPT
Second measurement
Correlation coefficient (r)
69.9 f 1.6 69.2+ 2.5
0.091 0.797*
(32.3 4.8 145.4 f5.1
132.9 f5.4 148.0 iz 5.4
0.874** 0.842**
73.5f2.9 8 1.3 f3.3
75.9 f3.0 84.1 f3.0
D.906**
0.247 f0.020 0.328 f0.024
0.230 f0.028 0.326 f0.036
0.882** 0.693*
0.095 f0.027 0.114f0.028
0.084 f0.023 0.098 f0.026
0.830** 0.862**
71.5f 1.9 71.6
+ 2.4
*
0.843* *
Correlation coefficients were obtained between the first and second measurements. Data are expressed as mean fs.e.m.
*P
