Hemodynamic effects of naloxone in hemorrhagic shock in pigs

The narcotic antagonist naloxone has been shown to reverse hypotension in hemorrhagic and septic shock in rats and dogs. This study was undertaken to investigate the hemodynamic effects of naloxone on hemorrhagic shock in the pig. Thirteen pigs were anesthetized with pentobarbital and were bled to a mean arterial pressure of 54% of the initial mean arterial pressure. Seven pigs received naloxone in increasing doses of 1.0, 2.5 and 5.0 milligram per kilogram intravenously, while the six pigs in the control group were given identical volumes of normal saline solution. Results indicate an increase in mean arterial pressure in the pigs of the naloxone group compared with that for the pigs in the saline solution treated group. There was no increase in cardiac output after the administration of naloxone or after the injections of saline solution. Peripheral vascular resistance increased in pigs in the naloxone group compared with that in pigs in the saline solution group. These results are in accordance with the concept that naloxone may reverse hypotension in hemorrhagic shock by antagonizing endogenous opiate-like substances and that the latter may be involved in the physiopathology of shock. The rapid increase in peripheral vascular resistance after the administration of naloxone suggests a change in sympathetic reflex as a possible mechanism of naloxone action.