Involvement of central histamine receptors in corticosterone secretion induced by intraventricular administration of morphine

The effect of intracerebroventricular (i.c.v.) administration of morphine on corticosterone secretion was studied in conscious, unstressed rats. A dose-dependent increase in serum corticosterone levels was observed 1 h after morphine injection. The corticosterone response to morphine was antagonized in a dose-dependent manner, and at larger dose almost abolished, by i.c.v. pretreatment of rats with naloxone, an opioid receptor antagonist. Intraventricular pretreatment of rats with mepyramine and cimetidine, the histamine H1- and H2-receptor antagonists, significantly diminished the corticosterone response to morphine. These results suggest that central opioid receptors are involved in the stimulating effect of morphine on the hypothalamo-pituitary-adrenocortical axis. Central histamine H1- and H2-receptors seem to be substantially involved in the stimulatory effect of morphine on corticosterone secretion in conscious, unstressed rats.