EFFECT OF BOTHROPS-INSULARIS VENOM ON THE MOUSE AND CHICK NERVE-MUSCLE PREPARATION

The effects of Bothrops insularis venom were examined in vivo in mice and chicks and in vitro using the mouse phrenic nerve diaphragm and ch ick biventer cervicis muscle preparations. Incubation of the indirectl y or directly stimulated mouse preparation with B. insularis venom (20 -80 mug/ml) produced an initial increase in twitch tension followed by irreversible blockade. With direct stimulation in the presence Of D-t ubocurarine, no increase in twitch tension was observed prior to the o nset of blockade. A venom-induced effect on presynaptic activity was s uggested by the marked increase in the frequency of the mepps recorded in vitro 5-15 min after venom addition. A direct muscular effect was shown by the dose- and time-dependent reduction in the resting membran e potential of the diaphragm. Chick preparations were more sensitive t han those of the mouse. In the isolated chick biventer cervicis muscle preparation, B. insularis venom induced a contracture and a dose-depe ndent block of responses to indirect stimulation. At low venom concent rations (1-5 mug/ml), no significant release of creatine kinase (CK) w as observed from this preparation. However, a dose-dependent release o f CK was detected at higher doses (10-80 mug/ml). For morphological st udies, B. insularis venom was injected into the chick left pectoralis muscle. At low doses (0.4 mug), only an inflammatory reaction was pres ent, while at high doses (20-80 mug) increasing numbers of necrotic fi bers were observed as well as occlusive thrombosis and hemorrhage. The muscular effect, also observed on the incubated muscle, points to a d irect myolytic action of the whole venom.