Pharmacological studies with scorpion (Palamneus gravimanus) venom: evidence for the presence of histamine

The venom from the scorpion Palamneus gravimanus caused, in cats, a pronounced hypotensive effect which was blocked by mepyramine. The hypotensive effect was observed in spinal and reserpinized cats, was not affected by carotid sinus and body denervation and bilateral vagotomy, and was not blocked by hexamethonium and atropine treatment. The venom produced hypertension in guinea pigs and rats which was blocked by tolazoline and in the case of the guinea pigs by mepyramine and by phenoxybenzamine in the rats. Treatment of rats with compound 48/80 did not prevent the hypertensive effect of the venom, showing that it is probably due to histamine or histamine-like substance in the venom and not due to releasing of histamine. Dialysis greatly attenuated the hypotensive effect and prevented the hypertensive action of the venom. Histamine in the venom was identified by paper chromatography, and biological assays showed a histamine-like activity corresponding to 5–7.2 μg histamine per mg dry venom. Both the crude and the dialysed venoms produced positive inotropic and chronotropic effects on isolated rabbit's heart that were not affected by pyribenzamine but were blocked by propranolol. The cardiac stimulant effect of the venom was absent in reserpinized hearts. It is concluded that histamine or histamine-like substance is present in P. gravimanus venom; however, all of the venom effects are not due to the presence of that substance.