Effect of morphine on the adrenal sympathetic reflex elicited by mechanical stimulation of the skin in rats.

The effect of morphine on the cutaneo-adrenal nerve reflex was studied in rats anesthetized with urethane-chloralose. Morphine (1 mg/kg, i.v.) significantly depressed the reflex increase in adrenal nerve activity induced by noxious lower chest pinching. Morphine (10 mg/kg, i.v.) significantly inhibited the reflex decrease in adrenal nerve activity induced by innocuous lower chest and hindlimb brushing, as well as the response induced by noxious lower chest pinching. Reversal by naloxone of the morphine-induced depression of the cutaneo-adrenal nerve reflexes indicates that the opioid receptor is associated with these effects of morphine.