Analgesic effect evoked by low molecular weight substances extracted from Crotalus durissus terrificus venom

Crude venom obtained from Crotalus durissus terrificus (Cdt) was tested for its possible analgesic effect in mice. Subcutaneous (s.c.), intraperitoneal (i.p.) or oral (p.o.) administration of the venom caused an antinociceptive effect in mice as measured by the acetic acid-induced writhing method and the hot plate test. The antinociceptive activity was dose and time dependent and persisted after neutralization of the venom with a specific antivenin. It was demonstrated that the factor(s) has an apparent mol. wt of less than 3000 and that its antinociceptive effect is abolished by trypsin treatment. The demonstration that morphine enhances the analgesic effect of Cdt venom and naloxone antagonizes this effect suggests an endorphin-like activity for the factor(s) herein described.