Cross-tolerance between ethanol and morphine in the guinea-pig ileum longitudinal-muscle/myenteric-plexus preparation

Morphinization of guinea pigs with s.c. implanted pellets (4 X 75 mg morphine base) has resulted in tolerance, within the isolated longitudinal muscle/myenteric plexus preparation, to the in vitro inhibitory effects of morphine on the electrically induced contractions, and in cross-tolerance to the inhibitory effects of ethanol. Similar results were observed with opiate-naive preparations that were incubated for 18 h in Krebs-Ringer solution containing 40 muM morphine. Daily ethanol injections (6 g/kg) resulted in tolerance to ethanol and cross-tolerance to morphine. These results suggest a commonality between ethanol and morphine actions on the myenteric plexus preparation.