Biphasic mechanical responses of the guinea-pig isolated ileum to the venom of the marine snail Conus striatus.

Venom extract of Conus striatus elicited a rhythmic, transient contraction of the guinea-pig isolated ileum followed by a relaxation at concentrations greater than 1 microgram/ml, which was abolished by tetrodotoxin and a low-Na medium. The contraction induced by the venom was inhibited by atropine but not mecamylamine, whereas the relaxation was not affected by bretylium, guanethidine or phentolamine. These results suggest that the contraction of the ileum induced by the venom is due to the excitation of cholinergic nerves, while the relaxation is mediated through non-adrenergic inhibitory nerves.