EFFECT OF MELATONIN ON ARGININE-VASOPRESSIN SECRETION STIMULATED BY PHYSICAL EXERCISE OR ANGIOTENSIN-II IN NORMAL MEN

The present study was undertaken in order to establish the possible in volvement of melatonin in the mechanisms underlying the arginine-vasop ressin (AVP) responses to physical exercise and angiotensin II (ANG II ). On two mornings at least 1 week apart, normal male subjects were te sted with exercise on a bicycle ergometer (the workload was gradually increased at 3-min intervals until exhaustion and lasted about 15 min in all subjects) or ANG II (60-min infusion of ANG II (Asp 1, IIe 5 an giotensin II) dissolved in 5% glucose in successively increasing doses of 4, 8, 16 ng/kg/min; each dose for 20 min). Tests were carried out with the administration of either 6 mg melatonin or placebo. Melatonin treatment neither modified the basal concentrations of AVP nor change d the AVP response to ANG II. In contrast, plasma AVP levels rose 3.6 times during exercise in the absence of melatonin, but only 2.3 times in the presence of melatonin. These data indicate an involvement of me latonin in the mechanism underlying the AVP response to physical exerc ise, but not ANG II, in normal men.