A POTENT FACTOR IN EXTRACTS OF THE SKIN OF THE AUSTRALIAN FROG, PSEUDOPHRYNE CORIACEA – APPARENT FACILITATION OF TRANSMITTER RELEASE IN ISOLATED SMOOTH MUSCLE PREPARATIONS

Extracts of the skin of the Australian frog Pseudophryne coriacea (PsC) displayed potent stimulant effects on isolated smooth muscle preparations of intestine and similar effects on electrically-stimulated vas deferens preparations. These effects must be ascribed to an alkaloid, related in structure to the pumiliotoxins, a class of alkaloid compounds occurring in the skin of neotropical poison frogs. On the basis of results obtained with antagonists and blocking agents, it is suggested that the extract has a pre-synaptic, neurogenic point of attack and that it acts to facilitate the release of transmitters from nerve endings. Acetylcholine is the most important agent involved in the response to the extract by the intestinal muscle and noradrenaline in the response by vas deferens preparations. However, release of other aminergic or peptidergic transmitters may participate, positively or negatively, in the response.