Acetylcholine release from the myenteric plexus of guinea-pig ileum by prostaglandin E1

Release of acetylcholine (ACh) by prostaglandin E1 from the nerve terminals of the guinea-pig longitudinal muscle strip was studied in order to reveal the effect of PGE1 on myenteric plexus activity. The ACh released was collected in the presence of physostigmine (2.1 microgram ml-1) and choline (0.1 microgram ml-1) at 38 degrees C. Five to 100 ng ml-1 PGE1 enhanced the release dose-dependently. The effect was maintained during the presence of PGE1 in the organ bath, while rapid tachyphylaxis was observed with the ACh-releasing action of nicotine. Tetrodotoxin or morphine almost completely inhibited the effect of PGE1 on ACh release. Hexamethonium, in a concentration which completely blocked the effect of nicotine, partially inhibited the effect of PGE1. In the late phase of nicotine action, the tissue was still sensitive to PGE1 despite the continued exposure to nicotine. These data suggest the presence in the myenteric plexus of PG receptors which can increase ACh release.