The role of vasopressin and the sympathetic nervous system in the cardiovascular response to vagal cold block in the conscious dog.

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Abstract
This study examined the role of arginine vasopressin in the pressor response to vagal cold block and evaluated a possible interaction between vasopressin and the sympathetic nervous system during vagal block in conscious dogs with (carotid sinus intact) and without (sinoaortic denervated) functional arterial baroreflexes. In both carotid sinus intact and sinoaortic denervated dogs, elimination of the arginine vasopressin pressor system by the specific vasopressin antagonist d(CH2)5Tyr(Me)AVP did not alter the response to vagal block, as evaluated by changes in arterial pressure. Subsequent removal of the sympathetic nervous system by ganglionic blockade abolished the response to vagal block. When ganglionic blockade was induced in the absence of the vasopressin antagonist, the pressor response to vagal block was reduced by only 60%. Arginine vasopressin antagonist after ganglionic blockade reduced the response to vagal block by an amount equivalent to 45% of the original increase in pressure. The effects of blockade of either vasopressin or the sympathetic nervous system on the pressor response to vagal block were significantly greater when the other system had previously been eliminated. Data suggest that both arginine vasopressin and the sympathetic nervous system contribute to the pressor response to vagal block. One interpretation of these results is that vasopressin also interacts centrally to inhibit sympathetic outflow and thus modulates the hemodynamic manifestation of interruption of vagal afferents.