Oxytocin antagonist disrupts hypotension-evoked renin secretion and other responses in conscious rats

Previous experiments have indicated that arterial hypotension increases pla sma oxytocin (OT) levels in rats and that OT infused intravenously causes a n increase in plasma renin activity (PRA). The goal of the present study wa s to determine whether systemic administration of an OT receptor antagonist would attenuate the increase in PRA that is normally evoked by arterial hy potension in rats. In conscious male rats, intravenous injection of hydrala zine or diazoxide produced sustained hypotension and evoked a significant i ncrease in PRA, as expected. Intravenous infusion of an OT receptor antagon ist did not alter the hypotension induced by hydralazine or diazoxide, but it did markedly blunt the induced increase in PRA. The OT receptor antagoni st also blunted the hypotension-evoked increase in heart rate and plasma va sopressin levels, suggesting that the antagonist may have generally disrupt ed afferent signaling of hypotension. Thus hypotension-evoked OT secretion may contribute to cardiovascular homeostasis by enhancing baroreceptor sign als that stimulate increases in renin secretion, vasopressin secretion, and heart rate during arterial hypotension in rats.