Kunihiko Yokotani and Yoshitsugu Osumi
Department of Pharmacology, Kochi Medical School, Nankoku, Kochi 783-8505,
Japan
Abstract: We examined the effect of endogenous opioid peptides on
vagally evoked release of acetylcholine (ACh) from the isolated, vascularly
perfused rat stomach. The vagus nerves were electrically stimulated twice
at 2.5 Hz for 2 min, and test substances were administered during the second
stimulation. beta-Endorphin (10-7 and 3 x 10-7 M),
an endogenous nonselective agonist of micro-receptors, inhibited the release
of ACh. However, [Leu5]-enkephalin, an endogenous nonselective
agonist of delta-receptors, and U-50488, a kappa-receptor agonist, had no
effect at a higher dose of 10-6 M. beta-Endorphin-induced inhibition
was abolished by naloxone. Endomorphins 1 and 2 (3 x 10-7 and
10-6 M), endogenous selective agonists of micro-receptors, also
inhibited the release of ACh. These results suggest that the micro-receptor
is involved in the endogenous opioid peptide-induced inhibition of the release
of ACh from the rat stomach.
Keywords: Acetylcholine release, Stomach, micro-Opioid receptor