Ionizing radiation induces opioid-mediated analgesia in male mice.

The effects of exposure to ionizing radiation on the nociceptive thresholds of CF-1 mice were examined. Significant increases in thermal response latencies, indicative of analgesia were observed after exposure to either high or low doses of radiation. However, the onset of analgesia occurred significantly more rapidly after treatment with the high doses. Administration of the opiate antagonist, naloxone, blocked and reversed the analgesic effects of both the high and low dose of radiation. These findings support the hypothesis that exposure to ionizing radiation results in opioid-mediated analgesia.