Reserpine inhibits release of vasopressin from the neural lobe of the pituitary in dehydrated rats.

The effects of reserpine on the osmotically induced release of pituitary vasopressin were studied (i) by measuring the urinary excretion and the vasopressin content of the neural lobe of pituitary, and (ii) by examining the ultrastructural morphology of axons in the neural lobe of dehydrated rats. After water deprivation for two days, control rats displayed characteristic antidiuretic response including a 75% reduction of urinary excretion and a six-fold decrease in vasopressin content of the neural lobe associated with a dramatic depletion of neurosecretory granules in corresponding axons. In contrast, when they received two dialy injections of reserpine, animals dehydrated for two days showed both urinary excretion and vasopressin contents in the neural lobe that remained at levels comparable to those measured in the normally hydrated rats. Additionally, neural-lobe axons of such dehydrated, reserpine-treated rats displayed a normal amount of neurosecretory granules. These data indicate that reserpine inhibits release of vasopressin from the neural lobe and favour the concept of a facilitatory role of the catecholaminergic innervation in the control of hypothalamo-neurohypophysial vasopressin-secreting neurons.