Baroreflex buffering of pressor response to vasopressin is mediated by V1, not V2, receptors in conscious rats.

Arginine vasopressin (AVP) enhances reflex buffering of its own pressor response, thus attenuating its vasoconstrictor potential in vivo. To investigate the extent to which this effect of AVP is mediated by V1 or V2 receptors, mean arterial pressure (MAP) and heart rate (HR) changes were examined in response to graded injections of AVP or [Phe2,Orn8]oxytocin, a potent, selective V1-receptor agonist, in the absence and presence of infusion of [Val4,D-Arg8]VP, a selective V2-receptor agonist. Responses were compared in intact and autonomically blocked conscious rats. During autonomic blockade with methscopolamine and hexamethonium, the pressor sensitivities to AVP and [Phe2,Orn8]oxytocin were similarly increased. Infusion of the V2-receptor agonist had no effect by itself on MAP or HR in conscious intact rats. It also did not alter the pressor responses to the V1 agonist, in either intact or autonomically blocked rats. In the presence of the V2 agonist, the decrease in heart rate induced by the V1 agonist was enhanced. These results indicate that reflex buffering of the pressor response to AVP in the conscious rat is mediated by V1 and not V2 receptors. However, V2 receptors may be involved in modulating the heart rate response to AVP.