PLASMA VASOPRESSIN AND OXYTOCIN IN RESPONSE TO EXERCISE AND DURING A DAY-NIGHT CYCLE IN MAN

Abstract

Plasma vasopressin (AVP) and oxytocin (OXT) were determined by radioimmunoassay in healthy young men before, during and after a running exercise until exhaustion. In 4 of the 5 test subjects (1 subject was underloaded) physical load resulted n a marked increase in plasma AVP with peak values of 11.7-57.8 pg/ml at exhaustion. Plasma OXT increased in 3 test subjects with peak values of 4.5-23.9 pg/ml. Within 1 h of recovery, both neuropeptides returned to basal plasma levels. The relationship between plasma AVP and osmolality (P < 0.001) suggests that changes in osmolality play a dominant role in regulating the secretion of AVP. Besides peripheral effects, the increased levels of AVP and/or OXT during and immediately after the exercise, respectively, might induce a favorable action on the brain function. Determination of plasma AVP and OXT during a day-night cycle in the same test subjects reveals increased AVP levels from 0200-0800 h as compared to the other time periods chosen (1800-2400 h, P < 0.001; 08.00 to 16.00 h, P = 0.031). In contrast, OXT does not differ between these time periods but decresed from 0800 to 1600 h (P < 0.01). Accordingly, no correlation exists between both neuropeptides suggesting an independent secretion. It is unclear whether the circadian variations shown are able to influence the neuropeptide response to exercise.