Possible involvement of epinephrine in the cardiovascular effect of naloxone in humans.

The opioid-receptor antagonist naloxone was administered intravenously in a 0.8-mg bolus to five healthy volunteers, aged 21 to 31, in a double-blind study designed to investigate the effect of endogenous opioids on blood pressure, heart rate, and urinary excretion of catecholamines in healthy adults. Three hours after administration of naloxone there were significant increases in systolic blood pressure (P less than 0.001) and heart rate (P less than 0.05). The amount of epinephrine excreted in urine during the four hours after administration of naloxone or placebo was significantly higher (P less than 0.05) in subjects given naloxone. These effects support the hypothesis that an endogenous opioid system is involved in the regulation of systolic blood pressure and heart rate in healthy adults. The results also indicate that adrenally released epinephrine could mediate the cardiovascular effect of endogenous opioids.