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4. Studies on the Mechanism of Action of Tityustoxin

Author

Freire-Maia, L., Cunha-Melo, J. R., Gomez, Marcus V., Tafuri, W. L., Maria, T. A., Calixto, S. L., Futuro-Neto, H. A., Ohsaka, Akira, editor, Hayashi, Kyozo, editor, Sawai, Yoshio, editor, Murata, Ryosuke, editor, Funatsu, Masaru, editor, and Tamiya, Nobuo, editor

Published
1976
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36. Evidence for a direct action of Tityus serrulatusscorpion venom on the cardiac muscle

Author

Teixeira, A.L, Fontoura, B.F, Freire-Maia, L, Machado, C.R.S, Camargos, E.R.S, and Teixeira, M.M

Abstract

The ability of toxins to activate the cardiovascular system plays an important role in the morbidity and lethality of the Tityus serrulatusscorpion envenoming. Most of the actions of the scorpion toxins are indirect and due to the release of adrenergic and cholinergic neurotransmitters. Accordingly, treatment following envenoming is targeted towards inhibition of adrenergic and cholinergic receptors. Here, we have sought evidence for a direct action of T. serrulatusvenom on the isolated rat heart (Langendorff's method). We show that the bradycardia induced by T. serrulatusvenom was completely blocked by atropine, a muscarinic receptor antagonist. Similarly, the increase in heart rate that follows the venom-induced bradycardia was totally inhibited by a β1-adrenoceptor antagonist or by chemical sympathetic denervation with 6-hydroxydopamine. In contrast to these findings, the venom-induced increase in contractile force was not modified by β1-adrenoceptor blockade or by chemical sympathetic denervation. The results clearly demonstrate that the chronotropic effects of T. serrulatusare dependent on neurotransmitter release, but the inotropic effects are not. The neurotransmitter-independent increase in contractility seems to be a direct action of the venom on cardiomyocytes. We suggest that this direct effect on cardiac fibers may play a role in the development of cardiac arrhythmias and contractility defects following envenoming with T. serrulatusscorpion.

Published
2001
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43. Hiperglicemia na intoxicação escorpiônica experimental em cão

Author

Ferreira C, Freire-Maia L, and Da Silva Cg

Subjects
Microbiology (medical), medicine.medical_specialty, Sympathetic nervous system, lcsh:Arctic medicine. Tropical medicine, biology, business.industry, lcsh:RC955-962, Scorpion, lcsh:QR1-502, Adrenergic, Blood sugar, Venom, lcsh:Microbiology, medicine.anatomical_structure, Endocrinology, Internal medicine, biology.animal, medicine, Liberation, Bilateral adrenalectomy, business
Abstract

The production of hyperglycemia during the acute phase of scorpion poisoning produced by T. bahiensis in dogs is confirmed now. The highest degree on average, was reached 10 minutes after the injection of venom. In our hands, the previous bilateral adrenalectomy did not avoid the hyperglycemia. The average of the blood sugar level has been similar to that observed in dogs with adrenal glands, the highest blood sugar level was also registered after 10 minutes. The hyperglycemia obtained in adrenolectomized dogs is, probably, due to the liberation of Sympatin (Nor-adrenalin and adrenalin) as a consequence of the central excitation by the poison on the hepatic nerves and other ganglionar terminations of the Sympathetic Nervous System. Our present researches suggest that the venom has adrenergic action besides the central action.

Published
1959

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