Cardiovascular and respiratory effects induced by intracerebroventricular injection of scorpion toxin (tityustoxin) in the rat

Abstract

The injection of 2·5, 5 and 10 μg of purified scorpion toxin (tityustoxin or TsTX) into the lateral ventricles of anesthetized rats caused dramatic effects on the circulatory and respiratory systems, consisting of hypotension, tachypnea, hyperpnea, ataxic and gasping breathing. Following these initial effects, 5 or 10 μg of TsTX induced hypertension and hyperpnea. The largest dose produced apnea and death about 70 min later. To study the mechanism of action of TsTX the intermediate dose (5 μg) was used. The early respiratory arrhythmias and hypotension were blocked centrally by atropine, but not by hexamethonium. In contrast, the late hypertension was blocked in part by central injection of phenoxybenzamine, but not by atropine or hexamethonium. Intravenous phenoxybenzamine partially antagonized the hypertensive effect, whereas i.v. guanethidine in bilateral adrenalectomized rats prevented the pressor effect induced by central injection of TsTX. The results indicate that the hypotensive effect and the early respiratory arrhythmias induced by intracerebroventricular TsTX are related to central muscarinic mechanisms. It is suggested that the late hypertension is due to the release of catecholamines from adrenal glands and postganglionic nerve fibers, as a consequence of central stimulation.