EVIDENCE THAT MORPHINE AND OPIOID PEPTIDES DO NOT SHARE A COMMON PATHWAY WITH ADENOSINE IN INHIBITING ACETYLCHOLINE RELEASE FROM ISOLATED INTESTINE

Abstract

The release of acetylcholine from isolated guinea pig ileal longitudinal muscle strip with intact Auerbach''s plexus was measured by bioassay and by a radioisotope technique. Normorphine (5 .times. 10-7 M) and D-Met2,Pro5-enkephalinamide (D-Met,Pro-EA) reduced the release of acetylcholine. Theophylline, an adenosine antagonist, failed to prevent the inhibitory effect of normorphine or D-Met,Pro-EA. Theophylline (1.7 .times. 10-4 M) by itself enhanced the twitch responses to field stimulation (0.1 Hz) but did not prevent inhibitory effect of normorphine and D-Met,Pro-EA. Morphine and opioid peptides apparently do not share a common pathway with adenosine in inhibiting acetylcholine release from axon terminals of Auerbach''s plexus.