A potent factor in extracts of the skin of the Australian frog, Pseudophryne coriacea--II. Stimulation of the leech helical muscle in vitro and in vivo.

Extracts of the skin of Pseudophryne coriacea displayed a powerful stimulant action on the leech helical muscle, both in vitro and in vivo. In the isolated dorsal muscle, the extract caused the appearance of vigorous phasic movements, accompanied by rapid increase in tonus, up to intense spasm. Hyoscine, physostigmine, hexamethonium, tubocurarine and alpha-bungarotoxin did not affect the response to the extract; tetrodotoxin, nifedipine and 5-hydroxytryptamine (5-HT) produced a partial blockade. In the intact animal, the extract at first potently stimulated the musculature, evoking the appearance of a succession of incoordinated, spastic movements, with twisting and rolling of the body of the animal. Stimulation was followed by paralysis and death. It is suggested that the pumiliotoxin-like alkaloid of Pseudophryne coriacea, responsible for these effects, acts directly on the helical muscle.