Evidence for the Differential Secretion of Oxytocin and Vasopressin in Man*

Abstract

Studies in 29 women during last weeks of pregnancy or during the first week of puerperium, or both, using their own changes in uterine activity (and intramammary pressure) and in urine osmolality as criteria of oxytocin and vasopressin release, respec-tively, showed that suckling and mammary duct dilation result in pro-nounced oxytocic/milk-ejecting activities and negligible antidiuresis. Nicotine and hypertonic saline result in marked antidiuresis and negli-gible oxytocic/milk-ejecting activities.These results demonstrate that oxytocic/milk-ejecting and antidiuretic activities can be manifested separately as the result of different stimuli to the neurohypophysis. These facts strongly suggest that oxytocin and vasopressin in man are released independently and that the pathways to the neurohypophysis or the releasing mechanisms, or both, are different for these hormones. It was also demonstrated that oxytocin and vasopressin do not act syner-gistically or antagonistically in their oxytocic/milk-ejecting and anti-diuretic activities.