Pfeuffer-Friederich_1985_Naunyn.Schmiedebergs.Arch.Pharmacol_331_311

The effects of lysergic acid diethylamide (LSD) on acetylcholine release and on smooth muscle tone were studied in the myenteric plexus-longitudinal muscle preparation of the guinea pig. LSD (0.01-10 microM) depressed in a concentration-dependent manner the electrically-evoked [3H]-acetylcholine outflow from strips preincubated with [3H]-choline. The maximal effect was a 45% inhibition by 1 microM LSD. The spontaneous outflow was not affected. Metitepine competitively antagonized (pA2 8.0) the LSD-induced reduction of the evoked outflow. Tolazoline and mepyramine did not affect the inhibitory action of LSD. The contractions in response to electrical stimulation were enhanced by 34% in the presence of 0.1 microM LSD. Other concentrations of LSD did not affect the twitches. LSD caused an increase in muscle tone which was antagonized non-competitively by mepyramine, metitepine and ketanserin. Ketanserin was a competitive antagonist against the histamine-induced contractions of the longitudinal muscle (pA2 8.49). The results suggest that LSD stimulates presynaptically located 5-HT receptors and thereby decreases the evoked acetylcholine release. In addition, LSD increases smooth muscle tone either directly through stimulation of H1 receptors or indirectly via histamine release.