Enhanced Analgesic Effects of Stress Following Chronic Administration of Naltrexone in Rats

Chronic administration of the long acting opiate antagonist naltrexone potentiated the analgesic effects of foot-shock stress in the hot-plate test in rats. No changes in pain responsiveness were noted in naltrexone-treated rats that were not subjected to the foot-shock treatment. The results suggest that chronic opiate receptor may lead to the development of supersensitivity in endogenous opiate systems that mediate the analgesic effects of stress.