Pulmonary vasoactive effects of exogenous and endogenous AVP in conscious dogs

Our objectives were to investigate the extent to which both exogenously administered and endogenously released arginine vasopressin (AVP) exert a direct, vasoactive influence on the pulmonary circulation of conscious dogs. Multipoint pulmonary vascular pressure-cardiac index (P/Q) plots were constructed during normoxia in conscious dogs by stepwise constriction of the thoracic inferior vena cava (IVC) to reduce Q. In intact dogs, AVP infusion (7.6 ng X kg-1 X min-1 iv) increased (P less than 0.01) plasma AVP from 2.3 +/- 0.4 to 280 +/- 23 pg/ml, and increased (P less than 0.01) the pulmonary vascular pressure gradient (pulmonary arterial pressure minus pulmonary capillary wedge pressure, PAP-PCWP) over the entire range of Q studied. Following administration of autonomic nervous system antagonists and a converting-enzyme inhibitor, exogenous AVP again increased (P less than 0.01) PAP-PCWP over the entire range of Q. Generation of P/Q plots via IVC constriction resulted in systemic hypotension (58 +/- 4 mmHg) and a concomitant increase (P less than 0.01) in endogenous AVP release from 2.1 +/- 0.2 to 109 +/- 22 pg/ml. Following administration of the specific AVP receptor antagonist [d(CH2)5]AVP (10 micrograms/kg iv), systemic arterial pressure, but not PAP - PCWP, was decreased to significantly lower levels as Q was reduced during IVC constriction. A similar response was observed in dogs pretreated with the neurohumoral blockers. Thus exogenous administration of AVP results in active, non-flow-dependent pulmonary vasoconstriction. This effect is not dependent on reflex activation of the autonomic nervous system or on the increased production of angiotensin II.(ABSTRACT TRUNCATED AT 250 WORDS)