Intracoronary naloxone in hemorrhagic shock: dose-dependent stereospecific effects.

Treatment with naloxone improves cardiovascular function and survival in a variety of shock models, and numerous sites and mechanisms for its action have been proposed. Data presented in this article support the hypothesis that in hemorrhagic shock naloxone exerts its beneficial hemodynamic effects by acting primarily at cardiac opiate receptors. Naloxone or its stereoisomer (d-naloxone) were administered intravenously (iv) and directly into the coronary circulation (ic) in dogs anesthetized with pentobarbital sodium and subjected to hemorrhagic shock. Treatment with naloxone (2.0 mg/kg iv or 0.2 mg/kg ic) resulted in significant improvements in arterial pressure, myocardial contractility, and cardiac output. Treatment with saline or naloxone (0.2 mg/kg iv) were without beneficial effect. The hemodynamic responses to naloxone administered into the coronary circulation were dose dependent and stereospecific. These data support the hypothesis that naloxone exerts its salubrious effects in canine hemorrhagic shock by acting at cardiac opiate receptors.