Circadian Variations of Plasma Renin Activity and Plasma Osmolality in Various Physiological and Pathological States

Circadian variations of plasma renin activity (PRA) and plasma osmolality (Posm) were simultaneously measured in 5 normal subjects and 32 patients with various diseases. Under the conditions studied, PRA in normal subjects exhibited a significant circadian variation with the maximum in the morning and the minimum in the late afternoon (p<0.01), while Posm showed a significant but reversed variation to that of PRA (p<0.01). There was a reciprocal correlation between individual values of PRA and Posm throughout a day (r=-0.564, p<0.01). These consistent circadian variations of PRA and/or Posm tended to be abolished in essential hypertension (EH), renovas-cular hypertension (RVH), primary aldosteronism, Cushing's syndrome, hyperthyroidism and chronic glomerulonephritis. Any correlation between PRA and Posm was not found in these disorders. However, the patients with hyperthyroidism tended to restore normal circadian variations of PRA and Posm after treatment with propranolol. When PRA value at 8:00 a.m. was compared with its median level for a day, there was a considerable difference without any correlation between them in the cases of EH and RVH. These results may support the concept that renin-angiotensin (RA) system is closely related to the physiological control of the body fluid and electrolytes and finely modulated under its pathological states. Clinically, it appears that a single determination of PRA may not be enough to detect the basal activity of RA system in various diseases. It should be requisite to consider about the circadian variation when PRA and Posm are evaluated for clinical purposes.