Microwave Facilitation of Methylnaltrexone Antagonism of Morphine-Induced Analgesia in Mice

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Abstract
Exposure to low dose microwave irradiation has been postulated to influence effects of centrally active pharmacological agents. In this investigation, the analgesic dose, 50% (AD50) for morphine in the mouse tail flick test was significantly increased by pretreatment with the centrally active opiate receptor blocker naltrexone, and the dose-response curve was shifted significantly to the right. On the other hand, the AD50 and dose-response curve for morphine were not influenced by either the peripherally active opiate receptor blocker methylnaltrexone alone or microwave irradiation (2.45 GHz, 20 mW/cm2, CW, 10 min) alone. However, following both methylnaltrexone pretreatment and microwave exposure, there was both a significant increase in the AD50 as well as a significant rightward shift of the dose-response curve, indicating a competitive antagonism of morphine by methylnaltraxone. One possible explanation for this microwave-drug interaction is that microwave energy might facilitate entry of methylnatrexone into the central nervous system.