Endorphins in primate hemorrhagic shock: beneficial action of opiate antagonists.

The endogenous opiate beta-endorphin is released concomitantly with adrenocorticotropin from the pituitary during stress. In the present study we investigated the possible involvement of opiate receptors in the cardiovascular depression associated with hypovolemic shock in the nonhuman primate. Changes in circulating levels in beta-endorphin were monitored during hemorrhagic shock in 18 female baboons. Plasma levels of beta-endorphin increased significantly during hemorrhagic shock and were significantly correlated with a decrease in cardiac output (P less than 0.05). Single bolus administration of the opiate receptor antagonist naloxone (2 or 5 mg/kg) produced a transient but significant improvement in cardiac output (P less than 0.05) and mean arterial pressure (P less than 0.05). Hemodynamic improvement was maintained with a constant infusion of naloxone. Opiate receptor blockade with the longer acting antagonist naltrexone (2 or 5 mg/kg) significantly increased mean arterial pressure (MAP; P less than 0.05), and CO (P less than 0.05), and decreased heart rate. Our results suggest that the baboon is an excellent model for the study of hemorrhagic shock and provide further evidence for endogenous opiate involvement in the cardiovascular pathophysiology of hemorrhagic shock.