AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 2 345-R349, Copyright © 1993 by American Physiological Society
Baroreflex buffering of pressor response to vasopressin is mediated by V1, not V2, receptors in conscious rats
K. Shimizu, J. Schwartz and B. P. McGrath
Monash University Department of Medicine, Monash Medical Centre, Melbourne, Victoria, Australia.
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.
