The black scorpion Heterometrus longimanus: pharmacological and biochemical investigation of the venom.

Documentation on the biological activity (including the lethality) of the venom (BSV) from the black scorpion Heterometrus longimanus is lacking. We have investigated the effects of BSV on adrenergic transmission using the rat isolated anococcygeus muscle (Acm), since the venom from several species of scorpions causes peripheral sympathetic nerve stimulation with enhanced adrenergic responses. The catecholamine content in BSV was also measured by HPLC. The effects of phentolamine (5 microM), guanethidine (5 microM), desipramine (1.5 microM), tetrodotoxin (2 microM) and reserpine pretreatment in vivo (5 mg/kg s.c. x 24 hr and 5 mg/kg i.p. x 3 hr) on contractile responses of the rat Acm to field stimulation, crude BSV (2-10 microliters in 6 ml bath), noradrenaline (3 microM), tyramine (10-15 microM), carbachol (2-3 microM) and potassium chloride (50-75 mM) were investigated. BSV mimicked the agonist actions of noradrenaline (NA) by acting directly on postjunctional alpha-adrenoceptors in the anococcygeus muscle. The LD50 of crude BSV injected i.v. into mice was 0.13 ml per kg mouse. Sequential ultrafiltration of the crude BSV revealed the presence of a substance of low mol. wt which mediates the postjunctional alpha-agonist actions of BSV. HPLC measurements confirmed the presence of noradrenaline (NA; mean concentration of 1.8 +/- 0.3 mM) in BSV; the dopamine concentration (mean of 31 +/- 4 microM) was 60-fold lower than that of NA, whereas adrenaline was not detected in all the 15 samples investigated. Thus, the presence of NA in BSV can account for the postjunctional alpha-agonist actions of the venom in the Acm.