Studies of diurnal changes in plasma renin activity, and plasma noradrenaline, aldosterone and cortisol...

Diurnal studies were performed on ten normal volunteers taking a normal sodium diet. Half-hourly blood samples were taken throughout 25 h and assayed for plasma renin activity (PRA) and the plasma concentrations of noradrenaline, aldosterone and cortisol. Sleep was recorded polygraphically and scored by standard criteria. Circadian rhythms were demonstrated for plasma cortisol, aldosterone and noradrenaline concentrations, but not for plasma renin activity. The nadir of the rhythm for the noradrenaline concentration appeared to be related to sleep itself rather than to any chronological index. Only PRA was effected by the stage of sleep, falling sharply during periods of REM sleep. Plasma cortisol and aldosterone concentrations showed a positive correlation over the 24 h. There was, however, no correlation between PRA and plasma aldosterone concentrations, except when the subjects arose after their night's recumbency. Plasma noradrenaline concentration did not correlate with the concentration of any of the other hormones measured.