The role of adrenal medulla and neurohypophysis in the central and peripheral cardiovascular effects of neurohypophysial peptides.

The cardiovascular effects of intravenous and intracisternal administration of neurohypophysial peptides were compared in normal, diabetes insipidus and adrenal demedullated chloralose anaesthetized dogs. In normal dogs, intravenous lysine vasopressin (0.1 to 100 mU/kg) induced a dose-dependent increase in blood pressure with bradycardia whereas intracisternal injection (0.01 to 10 mU/kg) elicited a dose-related decrease in blood pressure but no change in heart rate. Intracisternally injected oxytocin (1 and 10 mU/kg) increased blood pressure. The central hypotensive effects of vasopressin were not observed in diabetes insipidus or adrenal demedullated dogs. In contrast, the central pressor properties of oxytocin were still observed in these two groups of animals. These results show that the central cardiovascular properties of vasopressin (but not those of oxytocin) may vary according to the hormonal state of the animals. Intracisternal vasopressin induces an hypotensive response due to a decrease in sympathetic tone and dependent on the integrity of the neurohypophysial tractus.