Partial blockade by naloxone of clonidine-induced increase in plasma growth hormone in hypertensive patients.

Studies in animals and man indicate a functional interaction between the adrenergic and the opiate systems. In the present study the effect of the opiate receptor blocker naloxone on the increase in plasma GH induced by clonidine was investigated in eight patients with essential hypertension. In a randomized order the patients received a bolus dose of naloxone (10 micrograms/kg) or physiological saline followed by a slow infusion of naloxone (5 micrograms/kg X h) or saline, respectively. Fifteen minutes after the bolus dose of saline or naloxone, clonidine (3 micrograms/kg) was infused for 10 min. Clonidine induced a significant increase in plasma GH. Naloxone pretreatment resulted in a significantly reduced GH increase after the clonidine infusion. These results indicate that the clonidine-induced increase in plasma GH in hypertensive man is partly mediated via activation of opiate receptors which can be blocked by naloxone.