Investigação da atividade farmacológica induzida pelo veneno de rhinella schneideri sobre o sistema cardiovascular de insetos

Abstract

Rhinella schneideri is a toad of the Bufonidae family, native from South America, including Brazil. When in contact with air, its venom turn to a white yellow coloration, functioning as protection against microorganisms at the animal skin surface, as well as, defense against predators. Although, R. schneideri is a common specie encountered in many regions of Brazil, the pharmacology of its venom has not been cited in literature. The aim of this work was to show the pharmacological activity of toad venom R. schneideri in an experimental model of semi-isolated Phoetalia pallida heart (BAUMAN E GERSCH, 1982). The preliminary biochemical analysis of the venom demonstrated that it does not have anticholinesterasic activity. When cockroaches head homogenates were incubated with venom (32μg/g) no alteration of the enzyme activity was found. The addition of venom at cockroach semi-isolated heart preparation induced a concentration and time-dependent mode of action. In this set of experiments, venom (4, 16 and 32μg/g) induced a progressive negative chronotropic effect (decrease in the frequency of beats). The washing of preparations with insect saline was ineffective to reverse the inhibitory effect. The addition of epinephrine (5μM) after venom addition (32μg/g) in semi-isolated heart preparation reversed the negative chronotropic effect of venom. In conclusion we suggest that the venom of R. schneideri decreases the cockroach cardiac frequency by blocking the sodium-potassium ATPase pump at the insect heart. The venom does not interfere with cockroach acetylcholinesterase activity what is a reinforcement for the mechanism of action proposed.