The renin-angiotensin-aldosterone system and circadian rhythm of urine variables in normotensive and hypertensive subjects

Forty-two middle-age male subjects, aged from 47 to 54 years old, were divided into three groups; 14 normotensives (NT), 16 borderline hypertensives (BHT) and 12 hypertensives (HT). The environmental effects were neutralized as much as possible by keeping their activities synchronized and their plasma and urine variables simultaneously investigated using the same protocol as under normal physiologic conditions. The circadian rhythms of urinary excretions of Na, K, Cl, creatinine, aldosterone, adrenaline and noradrenaline were analyzed by a multivariate method (cosinor method). Both systolic and diastolic blood pressure were statistically significantly different among the three groups and body weight was greater in HT than in NT. Other plasma and urine variables examined, however, were not significantly different among the three groups. A statistically significant circadian rhythm was detected in the urine variables. The rhythm characteristics, such as the mesor, amplitude and acrophase, of the urine variables except for the acrophase of urinary Na excretion were not significantly different among the three groups; the circadian acrophase of urinary Na in HT and BHT appeared significantly earlier than in NT. The pathophysiological and clinical significance of the earlier appearance of the circadian acrophase of urinary Na in hypertensive subjects still remains a unique characteristic requiring further investigation.