Evidence for the presence of histamine in Gaboon viper (Bitis gabonica) venom

Venom from B. gabonica produced a dose-dependent contraction of both isolated guinea-pig ileum and rabbit aortic strip preparations. The venom-induced contraction was not antagonised by pretreatment with atropine, phentolamine, methysergide or indomethacin, however, it was blocked by the prior addition of chlorpheniramine or cyproheptadine. Upon exhaustive dialysis of the venom, the dialysate contracted both preparations, while the dialysed venom had no effect. Paper and thin-layer chromatography of the venom showed a spot with an Rf value corresponding to authentic histamine. Biological assay of the crude venom on the guinea-pig ileum showed that it contained the equivalent of 2-10 micrograms of histamine per mg dry weight of crude venom. pA2 values for chlorpheniramine using either the venom or histamine as agonists were not significantly different.