The direct effects of vasopressin on the resistance and capacitance properties of the pulmonary and systemic vasculature were studied in nine aneural dogs on systemic and pulmonary bypass. The systemic and pulmonary pressure-flow, the systemic and pulmonary arterial pressure-volume, and the systemic and pulmonary venous pressure-volume relationships were determined for five levels of infused vasopressin. Vasopressin levels of approximately 10, 30, 150, 300, and 500 pg/ml were achieved by intravenous infusions. Samples of venous blood were drawn before and after each set of pressure-flow and pressure-volume relationships for the determination of vasopressin level by radioimmunoassay. A linear relationship was found between vasopressin level and systemic vascular resistance. Systemic vascular resistance increased 0.072 +/- 0.011 mmHg.kg.min.ml-1 for a change in vasopressin level of 100 pg/ml. Vasopressin did not affect pulmonary vascular resistance or any vascular compliance. High doses of infused arginine vasopressin were necessary to elicit substantial vasoconstriction.
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