Vagal cold block in area postrema-lesioned dogs: interaction of vasopressin and sympathetic nervous system

Abstract

This study evaluated the interaction between arginine vasopressin (AVP) and the sympathetic nervous system (SNS) during bilateral vagal cold block (BVB) and the arterial baroreflex response to phenylephrine (PE) and exogenous AVP in conscious sham-operated (sham) and area postrema (AP)-lesioned mongrel dogs. The hemodynamic responses to ganglionic blockade (GB) and the vascular (V1) AVP receptor antagonist [d(CH2)5Tyr(Me)]AVP (AVPX) were similar in sham and AP-lesioned dogs. Elimination of the AVP pressor system by AVPX in sham dogs did not alter the pressor response to BVB, whereas subsequent blockade of the SNS by GB abolished the response to BVB. When GB was first imposed, however, it alone eliminated only 55% of the pressor response to BVB, whereas subsequent AVPX eliminated the remaining pressor response to BVB. In contrast, in AP-lesioned dogs, AVPX alone substantially reduced the pressor response to BVB. Additionally, the apparent contribution of each pressor system to the response to BVB was not enhanced in the absence of the other system, as had been seen in the sham dogs. These da ta indicate that during interruption of vagal afferent activity, reflexly released AVP appears to limit the reflex activation of the SNS. This interaction of AVP with the cardiopulmonary reflex is eliminated following ablation of the area postrema. Infusion studies with PE and AVP indicate that AVP significantly augments baroreflex inhibition of heart rate when compared with PE. Ablation of the area postrema did not alter the arterial pressure-heart rate relationship obtained with PE but eliminated the augmented response to AVP.(ABSTRACT TRUNCATED AT 250 WORDS)