Exogenous arginine vasopressin does not enhance carotid baroreflex control in the conscious dog

Arginine vasopressin (AVP) has profound effects on the cardiovascular system, yet has minimal pressor activity at physiological levels in intact subjects. We designed an investigation to delineate the effects of AVP on open-loop carotid baroreflex control of mean arterial pressure (MAP), total peripheral resistance (TPR), and cardiac output (CO) in conscious, chronically instrumented dogs. During graded infusions of AVP (0.5-2.0 ng.kg-1.min-1), the open-loop hemodynamic responses to controlled changes in isolated carotid sinus pressure (CSP) were determined. Increasing levels of AVP infusion led to significant increases in plasma AVP levels (P < 0.01). Increasing doses of AVP led to significant increases in TPR at all levels of CSP (P < 0.01). The overall range and gain of the response were not significantly different at any level of AVP infusion. Despite this increase in systemic resistance, there was no significant change in the MAP-CSP relationship. Infusion of AVP led to a dose-dependent depression in CO (P < 0.01) and heart rate (HR; P < 0.05) at all levels of CSP with no significant effect on open-loop baroreflex control. We conclude that although exogenous AVP induces profound changes in cardiovascular function, it does not alter carotid baroreflex control of MAP, TPR, CO, and HR.