Résumé
The neuromuscular effects of Bothrops neuwiedii pauloensis (jararaca-pintada) venom were studied on isolated chick biventer cervicis nerve-muscle preparations. Venom concentrations of 5-50 æg/ml produced an initial inhibition and a secondary increase of indirectly evoked twitches followed by a progressive concentration-dependent and irreversible neuromuscular blockade. At venom concentrations of 1-20 æg/ml, the responses to 13.4 mM KCl were inhibited whereas those to 110 æM acetylcholine alone and cumulative concentrations of 1 æM to 10 mM were unaffected. At venom concentrations higher than 50 æg/ml, there was pronounced muscle contracture with inhibition of the responses to acetylcholine, KCl and direct stimulation. At 20-24ºC, the venom (50 æg/ml) produced only partial neuromuscular blockade (30.7 ± 8.0 percent, N = 3) after 120 min and the initial inhibition and the secondary increase of the twitch responses caused by the venom were prolonged and pronounced and the response to KCl was unchanged. These results indicate that B.n. pauloensis venom is neurotoxic, acting primarily at presynaptic sites, and that enzyme activity may be involved in this pharmacological action