Evidence for the differential secretion of oxytocin and vasopressin

In the present study we have attempted to answer the question whether vasopressin and oxytocin are secreted together or independently. This subject has been a matter of controversy during the past 35 years. The great variety of methods used in measuring oxytocin and vaso-pressin activities, the variety of animal species studied, and the variety and magnitude of stimuli employed in different studies make it very difficult to compare results and to draw conclusions as to whether or not there may be independent release of these two neurohypophyseal hormones (1-5). The studies to be described in the present re-port have been performed in conscious women in whom several relatively mild stimuli known to act on the neurohypophysis were applied under care-fully controlled conditions. In the absence of adequate methods for assaying oxytocin and vaso-pressin directly in plasma, both hormones were assayed by indirect methods that have gained gen-eral acceptance. The results strongly suggest that under appropriate conditions oxytocin and vaso-pressin are released independently of each other by the human neurohypophysis. Methods Studies in 29 women were carried out during the last weeks of pregnancy (36 to 40 weeks) or during the first week of puerperium, or both. In preparation for the measurement of vasopressin activity, a constant degree of overhydration was in-duced by the oral administration of 10 to 20 ml of water per kg of body weight or the intravenous administration of a similar amount as 5 % glucose in water. Urine was collected through an indwelling catheter every 15 min