Evidence of an involvement of the opioid peptidergic system in the reaction to stressful conditions.

Rats exposed to combined cold and restraint exhibited reduced paw oedema following an injection of carrageenin. Under the same experimental conditions, the local inflammation became fully evident when animals were pretreated with naloxone, 5 mg/kg, s.c. The same dose of the narcotic antagonist also increased the intensity of gastric damage in restrained, cold-exposed rats. On the contrary, gastric ulcerations were practically inexistent in stressed rats treated with 10 mg/kg s.c. of morphine. It is suggested that the opioid peptidergic system is involved in the body's reactivity to stressful stimuli.