RESUMEN
Morphine antagonist naloxone (3mg/kgiv ) induced a rise in blood pressure,pulse pressure & respiratory rate in the rat under hemorrhagic shock. It also improved the survival rate. ?Receptor antagonist pheno-xybenzamine ( 1 mg/kg iv ) or adrenalectomy abolished the beneficial effects of naloxone. Reserpine ( 1 mg/kg ip for 5 d) which depleted catecholamines of periphal sympathetic nervous system could not abolish naloxone effects. Resrpine plus adrenalectomy abolished naloxone actions again. It is suggested that the effect of naloxone on the blood pressure is mainly due to release of catecholamine from adrenalmedu-llary. The results of isolated adrenal perfusion indicated that naloxone could not induce a rise in catecholamine concentration of perfused liquid. It is suggested that the action of naloxone on catecholamine release may not be a result of direct action upontbe chromaffin cells.