ACUTE ETHANOL EXPOSURE DECREASES THE ANALGESIC POTENCY OF MORPHINE INMICE

Chronic (7 days), forced ethanol drinking can decrease the analgesic p otency of opioid agonists in mice. In the present study, the effect of short-term ethanol treatment was examined using forced ethanol access and ethanol injection protocols. Mice were given forced access to 1, 3 or 7% (v/v) ethanol for 24 hr and then tested for s.c. morphine anal gesia using the tailflick assay. Controls had access to water. Another soup of mice was injected i.p. with 2.5 g/kg ethanol or water 4 times over a 21 hr period and tested 3 hr after the final injection for mor phine analgesia. Other mice were injected once i.p. with 1, 2 or 3 g/k g ethanol or water and tested 24 hr later using the tailflick. In the forced access study, ethanol dose-dependently decreased morphine's ana lgesic potency with the highest dose (7%) producing a 1.6-fold shift i n the ED50. This decrease in morphine potency was similar to that foun d in a related study using 7% ethanol for 7 days (1.8-fold shift). Rep eated ethanol injections significantly reduced the analgesic potency o f morphine (1.9-fold shift), whereas, a single injection of 1, 2 or 3 g/kg ethanol did not alter the potency of morphine. Control studies in dicated that neither 24 hr water nor food deprivation affected morphin e potency. Overall, these data show that sustained exposure to ethanol over a 24 hr period Will dose-dependently decrease morphine's analges ic potency. (C) 1998 Elsevier Science Inc.