Effects of lysine-vasopressin and oxytocin on central cardiovascular control

1 The cardiovascular effects of intravenous and intracisternal administration of neurohypophysial peptides were compared in dogs anaesthetized with chloralose. 2 Intravenous lysine-vasopressin (0.1 to 100 mu/kg) induced a dose-dependent increase in blood pressure and a decrease in heart rate. In contrast, intracisternal lysine-vasopressin (0.01 to 10 mu/kg induced a dose-related decrease in blood pressure and did not change heart rate. 3 Intracisternal oxytocin (1 and 10 mu/kg) increased blood pressure and did not change heart rate, whereas the same doses injected intravenously were inactive. 4 Pretreatment with guanethidine (15 mg/kg i.v. 24 h beforehand) abolished the hypotensive responses to intracisternal vasopressin but not the pressor action of intravenous vasopressin. 5 The pressor responses to central injections of oxytocin were not modified by guanethidine. 6 Hypotension elicited by intracisternal vasopressin was probably due to a decrease in sympathetic tone whereas the hypertension induced by intracisternal oxytocin was independent of variations in sympathetic tone.