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 lac king. We have investigated the effects of BSV on adrenergic transmissi on using the rat isolated anococcygeus muscle (Acm), since the venom f rom several species of scorpions causes peripheral sympathetic nerve s timulation with enhanced adrenergic responses. The catecholamine conte nt in BSV was also measured by HPLC. The effects of phentolamine (5 mu M), guanethidine (5 muM), desipramine (1.5 muM), tetrodotoxin (2 muM) 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 stimulati on, crude BSV (2-10 mul in 6 ml bath), noradrenaline (3 muM), tyramine (10-15 muM), carbachol (2-3 muM) and potassium chloride (50-75 mM) we re investigated. BSV mimicked the agonist actions of noradrenaline (NA ) by acting directly on postjunctional alpha-adrenoceptors in the anoc occygeus muscle. The LD50 of crude BSV injected i.v. into mice was 0.1 3 ml per kg mouse. Sequential ultrafiltration of the crude BSV reveale d the presence of a substance of low mol. wt which mediates the postju nctional 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 muM) 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 f or the postjunctional alpha-agonist actions of the venom in the Acm.