The analgesic action of narcotic analgesics and clopheline after the ionizing irradiation of rats

The ionizing radiation (150 Gy) extended the rat tail flick latency, decreased the pain-relief effects of morphine and opioids and enhanced the analgesic effect of clopheline. The radiation was followed by a decrease of vocalization threshold with a reduction of morphine- and clopheline-induced analgesia. Naloxone (0.1 mg/kg) eliminated the postradiation analgesia and did not change the hyperalgesic effect of the radiation.