beta-Adrenergic regulation of total systemic intravascular volume in the dog.

Abstract

.beta.-Adrenergic receptor stimulation is associated with an increase in venous return, but the mechanism by which this increase is mediated is not well defined. Dogs (55) were anesthetized, placed on cardiopulmonary bypass and perfused at a constant rate. In 23 of these animals changes in total systemic intravascular volume were measured as reciprocal changes in extracorporeal reservoir volume during isoproterenol (56 .mu.g/min) or norepinephrine infusion (30 .mu.g/min). At central venous pressures of 3, 8 and 13 cm H2O, isoproterenol was associated with decreases in intravascular volume of 70 .+-. 20 (standard error of the mean) (P < 0.02), 50 .+-. 20 (P < 0.05) and 20 .+-. 30 (nonsignificant) ml, respectively; norepinephrine was associated with decreases of 300 .+-. 60 (P < 0.001), 230 .+-. 30 (P < 0.001) and 190 .+-. 40 (P < 0.001) ml, respectively. The splanchnic vasculature was perfused selectively at a constant rate and drained separately in another 18 animals. In these dogs an isoproterenol-associated decrease in splanchnic volume occurred concomitantly with a decrease in postsinusoidal hepatic vascular resistance from 38 .+-. 5 to 18 .+-. 3 cm H2O.cntdot.min/l (P < 0.001). A norepinephrine-associated decrease in splanchnic volume occurred simultaneously with a decrease in hepatic vascular resistance from 33 .+-. 6 to 18 .+-. 2 cm H2O.cntdot.min/l (P < 0.001). The decreases in total intravascular volume obtained with isoproterenol or norepinephrine were abolished after the splanchnic vasculature was removed in 2 other animals. Decreases in hepatic resistance, splanchnoic volume and volume were abolished after propranolol. .beta.-Adrenergic receptor stimulation with isoproterenol or norepinephrine is associated with a decrease in transhepatic vascular resistance and subsequent decreases in splanchnic and total systemic intavascular volume.