Pumiliotoxin B-like alkaloid in extracts of the skin of the Australian myobatrachid frog Pseudophryne coriacea: effects on blood pressure and heart of the rabbit.

Extracts of the skin of the Australian myobatrachid frog Pseudophryne coriacea (PS) displayed striking, reversible and, in part, dose-dependent effects on the systemic blood pressure and the heart of the rabbit. Similarly to the results obtained in the rat, the blood pressure response in the rabbit consisted in an initial short-lasting fall, followed by a significant and persistent rise. The initial hypotensive effect was inhibited by atropine, indicating a cholinergic mechanism. The inhibition of the pressure rise by prazosin or guanethidine, but not by surrenalectomy or hexamethonium, suggests a catecholamine release from adrenergic nerve terminals of the vasculature. PS produced on the heart a variety of rhythm disorders, caused both by a release of acetylcholine and a direct effect on the myocardium. It is worth mentioning that tetrodotoxin, a typical sodium channel blocker, reduced or abolished the effects of PS both on the heart and the blood pressure, suggesting that sodium channels may directly or indirectly participate in the mechanism of action of PS.