The reversal of hemorrhagic hypotension by naloxone in conscious rabbits

Abstract

The effects of naloxone on blood pressure and heart rate were studied in conscious, chronically prepared rabbits. The effects of barbiturate anesthesia on the response to naloxone were investigated. Initial surgery to implant arterial and venous catheters was performed under halothane anesthesia. Experiments were begun 10 days-2 wk later. The rabbits were divided into 2 groups: a normotensive group and a group made hypotensive by hemorrhage. In the normotensive rabbits, naloxone (2 mg/kg i.v.) did not alter mean arterial blood pressure .**GRAPHIC**. pulse pressure (PP) or heart rate (HR). A 5 mg/kg dose increased .**GRAPHIC**. and PP, and decreased HR. In the hypotensive group, naloxone in a dose of 2, 3 or 5 mg/kg i.v. significantly increased .**GRAPHIC**. and PP while decreasing HR in a dose-related manner. A dose of 0.2 mg/kg did not significantly alter any of the measured parameters. Pentobarbital anesthesia significantly reduced the effects of the 3 mg/kg naloxone dose in the hypotensive group. These actions of naloxone may be mediated through antagonism of endogenous opiates.