Cardiac output distribution during vasopressin infusion or dehydration in conscious dogs

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Abstract
To better understand the role of arginine vasopressin in cardiovascular regulation, regional blood flows were measured in unanesthetized dogs with radioactive microspheres before and during 1-h vasopressin infusions that increased the vasopressin concentration of plasma by 11 .+-. 0.6 pg/ml. Cardiac output measured by an electromagnetic flowmeter decreased by 13%. Blood flows to the skeletal muscle and skin, the areas most affected, decreased by 30.8 and 34.3%, respectively. In the same group of dogs, a period of 48-h water restriction increased plasma vasopressin by 6.9 .+-. 1.3 pg/ml and reduced cardiac output by 14.4%. Skeletal muscle blood flow decreased by 32.8%, a pattern strikingly similar to that following vasopressin infusion. Obvious differences between vasopressin infusion and dehydration were noted, in particular in the skin and splanchnic areas. The possibility that vasopressin contributed to the cardiovascular adjustments to dehydration must be considered. The use of an antagonist of the vascular effects of vasopressin, [1-deaminopenicillamine, 2-(O-methyl)tyrosine]arginine-vasopressin [[dPTyr(Me)]AVP], did not permit clarification of this issue, because this analog given alone exerted pronounced systemic and regional cardiovascular effects that resembled those of vasopressin.