CIRCADIAN VARIATIONS OF ATRIAL-NATRIURETIC-PEPTIDE IN NORMAL PEOPLE AND ITS RELATIONSHIP TO ARTERIAL BLOOD-PRESSURE, PLASMA-RENIN ACTIVITY AND ALDOSTERONE LEVEL

To investigate the circadian variations of plasma atrial natriuretic p eptide (ANP) and its relationship to arterial blood pressure, plasma r enin activity and aldosterone level, we determined 24-h blood pressure in 14 healthy volunteers. Plasma ANP concentration, renin activity an d aldosterone levels were measured every 3 h by radioimmunoassay. We f ound no significant circadian variation of plasma ANP level (pg/ml) (d aytime level, 62 +/- 24 vs. night-time level, 57 +/- 19, P = 0.146) an d plasma renin level (ng/ml/h) (1.32 +/- 0.78 vs. 1.15 +/- 0.57, P = 0 .148), but there was diurnal change of blood pressure (mmHg) (systolic , 122 +/- 7 vs. 116 +/- 11, P < 0.001; diastolic, 80 +/- 11 vs. 72 +/- 11, P = 0.025) and plasma aldosterone level (pg/ml) (86 +/- 42 vs. 62 +/- 37, P < 0.001). The blood pressure and aldosterone levels reached maxima (11:00 h and 08:00 h, respectively) before that of ANP (17:00 h) and then decreased together until the nadir at 02:00 h. This might indicate that elevation of arterial blood pressure and plasma aldoster one level stimulate release of ANP under normal physiological conditio ns.