Journal of Gerontology: BIOLOGICAL SCIENCES 1992, Vol. 47, No. 6.B214-B219
Copyright 1992 by The Girontologiail Society of America
Effect of Aging on Circadian Rhythm of Atrial Natriuretic Peptide, Plasma Renin Activity, and Plasma Aldosterone Pietro Cugini,1 Piernatale Lucia,1 Loredana Di Palma,1 Massimo Re,1 Roberto Canova,2 Laura Gasbarrone,2 and Alberto Cianetti1
Atrial natriuretic peptide (ANP) shows a nychtohemeral fluctuation and an age-related trend. The aim of this study was to explore the circadian rhythm of ANP as a function of age. Circadian rhythms of plasma renin activity (PRA), aldosterone (PA), and cortisol (PC) were explored as well. Twenty clinically healthy subjects, 10 young (20-25 yrs) and 10 elderly (65-75 yrs), were investigated, while recumbent, after synchronization to light-dark regimen and meal timing. Blood samples for RIA tests were collected six times during the 24-hr span. The chronobiologic analysis in young subjects demonstrated a significant circadian rhythm for all the investigated variables with an acrophase-timing located at 16.48 for ANP, 4.44 for PRA, 5.32 for PA, and 7.12 for PC. In elderly subjects we documented an important increase of 24-hr mean plasma levels but not a statistically significant circadian rhythm for ANP, and a decrease in mean value of PRA which maintained, however, a significant periodic 24-hr oscillation in parallel with PA and PC. The results in young subjects reinforce the concept that ANP plays physiologically an inhibitory role on the phasic secretion of renin. The lack of the circadian rhythm for ANP along with the divergent changes in ANP and PRA 24-hr mean concentration of elderly subjects both suggest that ANP exerts with advancing age only a counterregulatory role on the tonic rather than the phasic release of renin.
T
HE circadian rhythm of atrial natriuretic peptide (ANP) as a function of age was explored in this study. Several publications have demonstrated that ANP is influenced by age(Grimaldietal., 1987; Halleretal., 1987; Ohashi etal., 1987; Clark et al., 1990). Other reports have documented that ANP is a molecule characterized by a periodic variability during the 24-hour span (Donckier et al., 1986; Richards etal., 1987a; Winters etal., 1988; Colantonio et al., 1989; Ehlenz et al., 1989; McCance et al., 1989; Zhang et al., 1989; Haak et al., 1990; Vesely et al., 1990). The purpose of this research was to detect the age-related relationships between the ANP circadian cycle and other variables involved in ion-water balance, including plasma renin activity (PRA) and plasma aldosterone (PA), whose physiology is characterized not only by a circadian rhythm (Armbruster et al., 1975; Katz et al., 1975; Cugini et al., 1981, 1984a, 1985) but also by an age-dependent trend (Crane and Harris, 1978; Cugini et al., 1982, 1987a). The study was integrated by the temporal assessment of plasma cortisol (PC) levels in order to explore a reference circadian rhythm. This investigation complements our previous research on the rhythmic functions of renin and aldosterone and other variables in elderly subjects (Cugini et al., 1982, 1985, 1987a). MATERIALS AND METHODS
Subjects and protocol. — The study was carried out on 20 clinically healthy young and old subjects: 5 males and 5 females (20-25 yrs old) and 5 males and 5 females (65-75 yrs). All subjects gave their informed consent to participate. B214
Young women were investigated during the follicular phase of their regular menstrual cycle, as renin and aldosterone are known to be influenced by the luteal production of progesterone. Blood collection was performed on the seventh day of a synchronizing protocol in which each subject followed a regimen of light-dark alternation (lights on: 0700, lights off: 2300) and a meal timing schedule (breakfast: 0830, lunch: 1230, dinner: 1830). The diet was normal in calories (25 KCal/Kg/day), contributed by 3 g/Kg/day of carbohydrates, 1 g/Kg/day of fats, and 1 g/Kg/day of proteins. Sodium and potassium intakes were, respectively, 2 mEq/Kg/day and 0.7 mEq/Kg/day, which is habitual in ordinary diets. The study of circadian rhythm of ANP, PRA, PA, and PC was performed in subjects lying in bed for 8 hours prior to the first blood draw; they maintained the supine posture all through the study. Blood (7 ml) for biochemical assays was collected by a non-thrombogenic catheter, previously inserted in an antecubital vein, at 0600, 0800, 1200, 1800, 2000, and 2400 hr. Blood samples were immediately centrifuged at 4 °C, and plasma was stored at — 40 °C until assay. Biochemical assay. — Plasma ANP, PRA, PA, and PC were measured by radioimmunoassay (RIA) according to methods described previously (Haber et al., 1969; Ruder et al., 1972; McKenzie and Clements, 1974; Richards et al., 1987b). The characteristics of RIA methods are reported in Table 1. Data series analysis. — The time-qualified raw values were analyzed as follows. First, data were organized in a
Downloaded from http://geronj.oxfordjournals.org/ at University of Southern California on April 2, 2014
'Chronobiologic Unit, University La Sapienza, Rome, Italy, department of Internal Medicine and Clinical Research Laboratory, S. Camillo De Lellis Hospital, Rome.
AGING AND CIRCADIAN RHYTHM OF ANP
Table 1. Characteristics of RIA Methods Used To Assay the Humoral Variables Investigated Coefficient of Variation for Precision (%)
ANP (pg/ml) PRA (ng/ml/h) PA (ng/dl) PC (mcg/ml)
Sensitivity
Intraassay
Interassay
10.0 0.008 3.5 2.5
7.0 5.5 8.0 6.5
10.0 16.6 10.7 15.2
Notes. ANP = atrial natriuretic peptide; PRA = plasma renin activity; PA = plasma aldosterone; PC = plasma cortisol.
tested by Bingham's test, a procedure for vectorial parameters (Bingham et al., 1982). RESULTS
The time-qualified mean values of the investigated variables are displayed in Figure 1. The temporal series show a within-day variability with a different height and shape in young individuals as compared to elderly subjects. The curve of ANP in young subjects shows a 24-h mean level of 57.5 pg/ml, a peak of 70.33 pg/ml, and a trough of 48.67 pg/ml. The ANP profile in aged people shows a 24-h mean level of 129.88 pg/ml, a peak of 144 pg/ml, and a trough of 111.2 pg/ml. A Mest found a significant difference between the 24-h mean levels of the two groups (p
Copyright 1992 by The Girontologiail Society of America
Effect of Aging on Circadian Rhythm of Atrial Natriuretic Peptide, Plasma Renin Activity, and Plasma Aldosterone Pietro Cugini,1 Piernatale Lucia,1 Loredana Di Palma,1 Massimo Re,1 Roberto Canova,2 Laura Gasbarrone,2 and Alberto Cianetti1
Atrial natriuretic peptide (ANP) shows a nychtohemeral fluctuation and an age-related trend. The aim of this study was to explore the circadian rhythm of ANP as a function of age. Circadian rhythms of plasma renin activity (PRA), aldosterone (PA), and cortisol (PC) were explored as well. Twenty clinically healthy subjects, 10 young (20-25 yrs) and 10 elderly (65-75 yrs), were investigated, while recumbent, after synchronization to light-dark regimen and meal timing. Blood samples for RIA tests were collected six times during the 24-hr span. The chronobiologic analysis in young subjects demonstrated a significant circadian rhythm for all the investigated variables with an acrophase-timing located at 16.48 for ANP, 4.44 for PRA, 5.32 for PA, and 7.12 for PC. In elderly subjects we documented an important increase of 24-hr mean plasma levels but not a statistically significant circadian rhythm for ANP, and a decrease in mean value of PRA which maintained, however, a significant periodic 24-hr oscillation in parallel with PA and PC. The results in young subjects reinforce the concept that ANP plays physiologically an inhibitory role on the phasic secretion of renin. The lack of the circadian rhythm for ANP along with the divergent changes in ANP and PRA 24-hr mean concentration of elderly subjects both suggest that ANP exerts with advancing age only a counterregulatory role on the tonic rather than the phasic release of renin.
T
HE circadian rhythm of atrial natriuretic peptide (ANP) as a function of age was explored in this study. Several publications have demonstrated that ANP is influenced by age(Grimaldietal., 1987; Halleretal., 1987; Ohashi etal., 1987; Clark et al., 1990). Other reports have documented that ANP is a molecule characterized by a periodic variability during the 24-hour span (Donckier et al., 1986; Richards etal., 1987a; Winters etal., 1988; Colantonio et al., 1989; Ehlenz et al., 1989; McCance et al., 1989; Zhang et al., 1989; Haak et al., 1990; Vesely et al., 1990). The purpose of this research was to detect the age-related relationships between the ANP circadian cycle and other variables involved in ion-water balance, including plasma renin activity (PRA) and plasma aldosterone (PA), whose physiology is characterized not only by a circadian rhythm (Armbruster et al., 1975; Katz et al., 1975; Cugini et al., 1981, 1984a, 1985) but also by an age-dependent trend (Crane and Harris, 1978; Cugini et al., 1982, 1987a). The study was integrated by the temporal assessment of plasma cortisol (PC) levels in order to explore a reference circadian rhythm. This investigation complements our previous research on the rhythmic functions of renin and aldosterone and other variables in elderly subjects (Cugini et al., 1982, 1985, 1987a). MATERIALS AND METHODS
Subjects and protocol. — The study was carried out on 20 clinically healthy young and old subjects: 5 males and 5 females (20-25 yrs old) and 5 males and 5 females (65-75 yrs). All subjects gave their informed consent to participate. B214
Young women were investigated during the follicular phase of their regular menstrual cycle, as renin and aldosterone are known to be influenced by the luteal production of progesterone. Blood collection was performed on the seventh day of a synchronizing protocol in which each subject followed a regimen of light-dark alternation (lights on: 0700, lights off: 2300) and a meal timing schedule (breakfast: 0830, lunch: 1230, dinner: 1830). The diet was normal in calories (25 KCal/Kg/day), contributed by 3 g/Kg/day of carbohydrates, 1 g/Kg/day of fats, and 1 g/Kg/day of proteins. Sodium and potassium intakes were, respectively, 2 mEq/Kg/day and 0.7 mEq/Kg/day, which is habitual in ordinary diets. The study of circadian rhythm of ANP, PRA, PA, and PC was performed in subjects lying in bed for 8 hours prior to the first blood draw; they maintained the supine posture all through the study. Blood (7 ml) for biochemical assays was collected by a non-thrombogenic catheter, previously inserted in an antecubital vein, at 0600, 0800, 1200, 1800, 2000, and 2400 hr. Blood samples were immediately centrifuged at 4 °C, and plasma was stored at — 40 °C until assay. Biochemical assay. — Plasma ANP, PRA, PA, and PC were measured by radioimmunoassay (RIA) according to methods described previously (Haber et al., 1969; Ruder et al., 1972; McKenzie and Clements, 1974; Richards et al., 1987b). The characteristics of RIA methods are reported in Table 1. Data series analysis. — The time-qualified raw values were analyzed as follows. First, data were organized in a
Downloaded from http://geronj.oxfordjournals.org/ at University of Southern California on April 2, 2014
'Chronobiologic Unit, University La Sapienza, Rome, Italy, department of Internal Medicine and Clinical Research Laboratory, S. Camillo De Lellis Hospital, Rome.
AGING AND CIRCADIAN RHYTHM OF ANP
Table 1. Characteristics of RIA Methods Used To Assay the Humoral Variables Investigated Coefficient of Variation for Precision (%)
ANP (pg/ml) PRA (ng/ml/h) PA (ng/dl) PC (mcg/ml)
Sensitivity
Intraassay
Interassay
10.0 0.008 3.5 2.5
7.0 5.5 8.0 6.5
10.0 16.6 10.7 15.2
Notes. ANP = atrial natriuretic peptide; PRA = plasma renin activity; PA = plasma aldosterone; PC = plasma cortisol.
tested by Bingham's test, a procedure for vectorial parameters (Bingham et al., 1982). RESULTS
The time-qualified mean values of the investigated variables are displayed in Figure 1. The temporal series show a within-day variability with a different height and shape in young individuals as compared to elderly subjects. The curve of ANP in young subjects shows a 24-h mean level of 57.5 pg/ml, a peak of 70.33 pg/ml, and a trough of 48.67 pg/ml. The ANP profile in aged people shows a 24-h mean level of 129.88 pg/ml, a peak of 144 pg/ml, and a trough of 111.2 pg/ml. A Mest found a significant difference between the 24-h mean levels of the two groups (p
