Cardiocirculatory effects of physiological doses of beta-endorphin

Beta-endorphin has been implicated in the cardiovascular depression that occurs in shock. While pharmacologic doses of beta-endorphin cause hypotension, physiologic doses of beta-endorphin have not been studied. In this study, six dogs (group I) were given IV beta-endorphin (peak concentrations previously determined in canine shock, 3,200 pg/ml); 5 minutes prior to beta-endorphin infusion, four dogs (group II) were given naloxone, 2 mg/kg bolus, and continuous infusion, 2 mg/kg/hr. In group I, beta-endorphin decreased stroke volume (from 0.99 +/- .12 to 0.57 +/- .08 ml/kg), dP/dt (from 3,167 +/- 140 to 2,875 +/- 412 mmHg X sec), and coronary blood flow (from 2.5 +/- .47 to .68 +/- .11 ml/min/gm), while heart rate rose significantly. Naloxone pretreatment maintained dP/dt, stroke volume, and coronary blood flow with no change in heart rate or mean arterial pressure. This study confirms that beta-endorphin depresses contractility and coronary blood flow in normovolemic nonstressed dogs, suggesting that beta-endorphin is in part responsible for cardiovascular depression in shock.