Oxytocin-induced renin secretion in conscious rats

Arterial hypotension and hypovolemia are known to stimulate neurohypophysia l secretion of oxytocin (OT) in rats, although the physiological function o f OT under these circumstances is uncertain. We now report that OT infused intravenously into conscious rats at 125 ng . kg(-1) . h(-1), a dose select ed to mimic plasma OT levels during hypotension or hypovolemia, increased p lasma renin concentration and plasma renin activity by twofold. This effect was prevented by systemic pretreatment with an OT receptor antagonist ([1- (3-mercaptopropionic acid)-2-O-ethyl-D-Tyr-Thr(4)-Orn(8)]-OT]. The OT antag onist did not block renin secretion induced by systemic injection of the be ta-adrenergic receptor agonist isoproterenol, indicating that the OT antago nist does not interfere nonselectively with renin release. Pretreatment of rats with the beta-adrenergic receptor antagonist nadolol also prevented OT -induced renin secretion. Similarly, nadolol injected during infusion of OT markedly reduced the elevated plasma renin levels. These observations rais e the possibility that pituitary OT secretion during hypotension or hypovol emia in rats may serve to support Mood pressure by enhancing activation of the renin-angiotensin system via a beta-adrenergic receptor-dependent mecha nism.