The action of eledoisin on the peristaltic reflex of guinea-pig isolated ileum.

1. Low concentrations of eledoisin, acting from the serosal surface of the guinea-pig isolated ileum, had no effect on the peristaltic reflex, whereas in high concentrations it depressed or sometimes abolished this reflex.2. Eledoisin stimulated the peristaltic activity of the guinea-pig ileum subjected to continuously raised intraluminal pressure. This stimulatory effect could be produced regularly when the interval between additions of eledoisin was at least 20 min. When added at shorter intervals, tachyphylaxis to eledoisin developed, but its ability to promote peristaltic activity was restored by the addition of an anticholinesterase to the bath fluid. During tachyphylaxis to eledoisin, nicotine and dimethylphenylpiperazinium were unable to restore peristalsis.3. When the peristaltic reflex had been abolished by ganglion-blocking agents, morphine and morphine-like substances, or adrenaline, eledoisin restored the reflex. Eledoisin was much more effective in overcoming the blocking effect of hexamethonium, tetraethylammonium and azamethonium than that of nicotine or dimethylphenylpiperazinium.4. Eledoisin did not antagonize the inhibitory effects of atropine, hyoscine and hyoscine butylbromide.5. It is suggested that the stimulant effect of eledoisin may be due to a direct action on the smooth muscle and a release of acetylcholine from postganglionic nerve endings, but an effect on the intestinal ganglion cells cannot be excluded.