Effects of naloxone and morphine in hemorrhagic shock

The effects of naloxone hydrochloride and morphine sulfate on survival were examined in LD40 hemorrhagic shock in rats. Bolus IV injection of naloxone (1.6 mg/kg) following hemorrhage significantly (p less than 0.025) increased the 24 hour survival rate (14/15, 93%), compared to that in saline-treated animals (13/22, 59%). Supraphysiologic doses of IV morphine sulfate did not adversely influence survival (12/15, 80% at 0.5 mg/kg; 8/15, 53% at 0.1, 0.05, and 0.01 mg/kg). Morphine decreased heart rate during shock in a dose-dependent fashion, but did not affect the blood pressure. Compared to responses in the other groups, naloxone had no effect on blood pressure or heart rate in shock animals during the monitoring interval. These results suggest that: 1) endogenous opioid substances, most likely at much lower blood concentrations than those used in the present experiment, may not be important deleterious factors during shock; and 2) enhancement of survival by naloxone in hemorrhagic shock is probably due to effects other than antiopiate activity.