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.