Further Studies on the Capacity of the Neurohypophysis To Release Vasopressin¹

The dog neurohypophysis can release only a fraction of the vasopressin (ADH) it contains in response to repeated stimulation in vivo or in vitro. Experiments have been performed to determine whether this limited release might result from the presence of ADH in the medium or from cellular damage due to anoxia or substrate deprivation. Neural lobes from bled dogs took up O2 in vitro at almost twice the rate of neural lobes from unbled animals. Excess K+ in the incubation medium enhanced the rate of O2 consumption in both cases. Incubation of posterior pituitaries (from unbled dogs) in media lacking glucose and O2 resulted in an increase in the basal level of ADH secretion, and a marked inhibition in the rate of hormone release in response to 56 HIM K+. The secretory mechanisms did not appear to have suffered permanent damage due to the extensive period of hypoxia and substrate deprivation. One hr after the readmission of glucose and O2 to the medium, such pituitaries released ADH in response to 56 HIM K+ at...