Diurnal variation of plasma vasopressin in man

Abstract

Plasma arginine vasopressin (PAV) concentration was determined by radioimmunoassay during the diurnal cycle in 8 recumbent healthy male subjects. Two subjects were studied again 3 weeks later while receiving 1 mg of dexamethasone every 6 h. Hematocrit and plasma osmolality were determined in 6 cycles. In 8 out of 10 cycles, a nocturnal increase in PAV was found; there was a progressive rise during the night in 5 subjects and a peak occurred at 2400 or 0400 h. In 1 subject no variation was detected and in another, the pattern was completely different. The mean PAV in the 10 cycles was significantly (P < 0.001) higher during the night than during the day. Dexamethasone did not modify the pattern of variation, but induced a significant (P < 0.001) decrease in PAV. Hematocrit remained stable throughout the study as did osmolality, except at 2000 h, when a significant (P < 0.001) increase (5 mOsm) on average occurred in every subject. Blood sugar, sodium or chloride did not account for the observed rise in osmolality and no simultaneous change in PAV occurred. A rise in PAV explains, to some extent, the known nocturnal decrease in urine output. Diumal variation in PAV must be taken into account in clinical investigations involving vasopressin. © 1975 by The Endocrine Society.