EFFECT OF VASOPRESSIN ON SYSTEMIC CAPACITY

To assess the effect of vasopressin (VP) on systemic capacity (SC), blood was drained from the venae cavae to an oxygenator and returned to the aorta at a constant rate so that changes in SC could be measured as the inverse of changes in oxygenator volume in 17 anesthetized pigs. After 10 min of VP administration (1.1 U/min ia), mean arterial pressure increased from 67 +/- 2 to 144 +/- 7 mmHg (P < 0.001). SC decreased promptly and reached a nadir of 110 +/- 32 ml (P < 0.02, 5.5 ml/kg) below control at 5 min but returned to 35 +/- 65 ml (P = not significant, 1.8 ml/kg) below control at 10 min. Portal venous pressure decreased from 19.3 +/- 2.6 to 16.6 +/- 2.7 mmHg (P < 0.001), and portal flow decreased from 828 +/- 68 to 458 +/- 92 ml/min (P < 0.001). Transhepatic venous resistance increased. After evisceration, VP caused only an increase in SC. Thus VP causes an initial SC decrement due entirely to a decrease in splanchnic capacity. The decrease in splanchnic capacity must be caused, at least in part, by the decrease in gastrointestinal arterial inflow and subsequent decrease in portal venous pressure. These initial effects of VP on SC would be expected to enhance ventricular filling and cardiac output in the intact animal and could be important in the acute compensatory response to hemorrhage.