Propofol-induced increase in vascular capacitance is due to inhibition of sympathetic vasoconstrictive activity

Background Venodilation is thought to be one of the mechanisms underlying propofol-induced hypotension. The purpose of this study is to test two hypotheses: (1) propofol increases systemic vascular capacitance, and (2) the capacitance change produced by propofol is a result of an inhibition of sympathetic vasoconstrictor activity, Methods: In 33 Wistar rats previously anesthetized with urethane and ketamine, vascular capacitance was examined before and after propofol infusion by measuring mean circulatory filling pressure (P-mcf). The P-mcf was measured during a brief period of circulatory arrest produced by inflating an indwelling balloon In the right atrium. Rats were assigned into four groups: an intact group, a sympathetic nervous system (SNS)-block group produced by hexamethonium infusion, a SNS-block + noradrenaline (NA) group, and a hypovolemic group. The P-mcf was measured at a control state and 2 min after a bolus administration of 2, 10, and 20 mg/kg of propofol, Results: The mean arterial pressure (MAP) was decreased by propofol dose-dependently in intact, hypovolemic, and SNS-block groups, but the decrease in MAP was less in the SNS-block group (-25%) than in the intact (-50%) and hypovolemic (-61%) groups. In the SNS-block + NA group, MAP decreased only at 20 mg/kg of propofol (-18%), The P-mcf decreased in intact and hypovolemic groups In a dose-dependent fashion but was unchanged in the SNS-block and SNS-block + NA groups. Conclusions: The results have provided two principal findings: (1) propofol decreases P-mcf dose-dependently, and (2) the decrease In P-mcf by propofol is elicited only when the sympathetic nervous system is intact, suggesting that propofol increases systemic vascular capacitance as a result of an inhibition of sympathetic nervous system.