Snake venoms frequently vary in composition. In this work, we compared the neurotoxic and myotoxic activities of 16 lots of Bothrops neuwiedii venoms from different regions of Brazil, using chick biventer cervicis preparations. The neuromuscular blockade varied from 2% to 100% after 120 min incubation with venoms (50 mug/ml). In all cases, this blockade was irreversible and concentration-dependent; at low concentrations (10-20 mug/ml), 15 of the 16 venom lots failed to abolish responses to acetylcholine (110 muM), but blocked responses to KCl (13.4 muM), and induced contracture. At 5-20 mug/ml, the most active venom totally blocked twitch-tension without affecting responses to acetylcholine and KCl. Polyacrylamide gel electrophoresis for basic proteins showed that the most active samples contained a band that was absent in the less active venoms. These results indicate that there may be considerable intraspecific variation in the neurotoxic activity of B. neuwiedii venoms, whereas myotoxic activity is less variable.

Bothrops jararacussu venom and its major toxin bothropstoxin-I (BthTX-I) possess myotoxic and neurotoxic properties. The efficacy of a rabbit antivenom raised against B. jararacussu venom in the neutralization of physiological, biochemical, and morphological changes induced by the venom and its major toxin BthTX-I was studied in mouse isolated phrenic nerve-diaphragm (PND) and extensor digitorum longus (EDL) preparations. The times required for 50% neuromuscular blockade in PND and EDL preparations for venom were 70+11.5 (S.E.M., n=5) min and 58+8 (n=16) (50 mu g/mL), and for BthTX-I 31+6 (n=3) min and 30+3 (n=5) min (20 mu g/mL), respectively. After 120 min incubation, creatine kinase (CK) concentrations in solution containing the EDL preparations were 3464+346 U/L after exposure to venom (50 mu g/mL, n=5) and 3422+135 U/L to BthTX-I (20mu g/mL, n=4), respectively. Rabbit antivenom dose-dependently neutralized venom and toxin-induced neuromuscular blockade in both preparations and effectively prevented venom and toxin-induced CK release from EDL. Histological analysis showed that rabbit antivenom neutralized morphological damage caused by B. jararacussu venom and BthTX-I in EDL preparations. These results indicate that rabbit antivenom effectively neutralized the biological activities of B. jararacussu venom and BthTX-I.