Pharmacological evidence for a presynaptic action of venoms from Bothrops insularis (jararaca ilhoa) and Bothrops neuwiedi (jararaca pintada).

Abstract Whereas the presynaptic action of Crotalus durissus terrificus venom is well-established, Bothrops venoms have historically been considered to have only postsynaptic and muscular effects. However, some studies have also suggested a presynaptic action for these venoms. In this work, we used chick biventer cervicis preparations to compare the presynaptic actions of two Bothrops venoms ( B. insularis and B. neuwiedi ) with that of C. d. terrificus venom. At 10 μg/ml, all venoms produced irreversible blockade of the twitch tension responses, with no reduction in acetylcholine (ACh)-induced contractures and only a slight decrease in potassium induced-contractures. The times (in min) required to produce 50% neuromuscular blockade ( C. d. terrificus : 16.3±0.7, n =8; B. insularis : 30.0±1.9, n =5; B. neuwiedi : 42.0±2.0, n =8; mean±SEM) were significantly different among the venoms ( p B. insularis and B. neuwiedi venoms. These observations indicate that bothropic venoms may contain components which act presynaptically in a manner similar to C. d. terrificus venom, and that at low venom concentrations a direct action on skeletal muscle does not contribute to this presynaptic neurotoxicity.