CATECHOLAMINERGIC MEDIATION OF MORPHINE-INDUCED ACTIVATION OF PITUITARY-ADRENOCORTICAL AXIS IN THE RAT - IMPLICATION OF ALPHA-ADRENOCEPTORSAND BETA-ADRENOCEPTORS

The present study investigates the role of hypo thalamic catecholamine s in the effects of morphine on hypothalamo-pituitary-adrenocortical ( HPA) axis. Acutely administered morphine (30 mg/kg i.p) increased plas ma corticosterone and reduced the hypothalamic noradrenaline (NA) cont ent but it did not change either the dopamine (DA) concentration or th e ratio DOPAC/DA. After reserpine administration the hypothalamic cont ents of NA and DA were drastically reduced without changing plasma cor ticosterone concentrations. The increase in plasma corticosterone indu ced by morphine was significantly reduced by the pretreatment with res erpine. The alpha(1)- and alpha(2)-antagonists prazosin and yohimbine, respectively, significantly antagonized the effect of morphine on pla sma corticosterone. The beta-antagonist propranolol also significantly attenuated the increase of corticosterone secretion induced by morphi ne. The results suggest that the action of the opiate on HPA axis acti vity may be dependent on stimulatory catecholaminergic systems which u tilize alpha(1)-, alpha(2)- and beta-adrenoceptors.