BRAZILIAN SCORPION VENOM (TITYUS SERRULATUS), AN UNUSUAL SYMPATHETIC POSTGANGLIONIC STIMULANT

¹ Department of Pharmacology, Faculty of Medicine of Ribeirão Prêto, University of São Paulo, São Paulo, Brazil

An extract of Brazilian scorpion venom was assayed upon the isolated heart of the guinea pig. The typical effect of the venom, in final concentrations of the order of 10^-6 g/ml, is a short-lasting bradycardia followed by a conspicuous increase in the force and the frequency of cardiac contractions. The venom also produces a marked rise in the phosphorylase a activity of the perfused heart. The bradycardia is blocked by atropine (1O^-5 g/ml) and potentiated by neostigmine (10^-6 g/ml). The cardiac stimulation is abolished by the beta sympatholytic agent propranolol (1O^-7 g/ml) and by the adrenergic blocking agent bretylium (1O^-5 g/ml); the cardiac stimulation is also absent in the hearts of reserpine-treated guinea pigs. Hexamethonium (1O^-5 g/ml) does not affect either the bradycardia or the cardiac stimulation elicited by the venom in doses which abolish the effects of nicotine. It is concluded that 1) both effects of the venom are indirect and due to a local release of acetyicholine and norepinephrine, and 2) the site of action of the venom is the postganglionic nerve terminals.