Further studies on the mechanism of vasodepressor response in cats after intravenous administration of venom from the snake Dendroaspis jamesoni (Jameson's mamba)

Further studies on the mechanism of vasodepressor response in cats after intravenous administration of venom from the snake Dendroaspis jamesoni (Jameson's mamba). Toxicon 15, 561–570, 1977.—Intravenous administration of Dendroaspis jamesoni venom in cats produced a biphasic vasodepressor response; an initial brief fall followed by a sustained secondary hypotension. Prior atropine administration abolished the initial hypotensive response and the secondary fall was prevented by transection of spinal cord at C 2. In spinal cord transected and atropinized animals, both vasodepressor components were absent. Chromatographic analysis of the venom provided two fractions which were eluted with normal saline and administered i.v. Fraction 1 whose migration was very close to that of acetylcholine produced a brief hypotensive response which was abolished by prior atropinization. Administration of other fraction, with slower migration characteristics, produced a sustained vasodepressor phenomenon. Five fractions of the venom were separated by starch gel electrophoresis. Of these, fraction V also caused a sustained fall in blood pressure which was abolished after transection of spinal cord (C 2). On the basis of present observations and those reported earlier, a cholinergic mediation for the initial fall in the blood pressure and a central locus of action possibly at the vasomotor centre for the sustained secondary hypotension is suggested.