VERATRIDINE BLOCKADE OF THE CAROTID SINUS PRESSORECEPTORS

¹ Laboratory of Chemical Pharmacology, The National Heart Institute, Bethesda 14, Maryland
² The Department of Pharmacology, Emory University School of Medicine, Emory University, Georgia

1. Injections of small doses of protoveratrine (0.1 microgm.), neogermitrine (0.05 microgm.), and andromedotoxin (0.1 microgm.) into the adventitia of the innervated carotid sinus of vagotomized dogs with unilateral carotid sinus denervation result in a fall in arterial blood pressure and blockade of the carotid sinus pressor reflex.

2. Veratridine injected in a similar manner has no effect at a dose of 0.1 microgm., but at 0.5 to 1 microgm. causes a pronounced rise in arterial pressure with a blockade of the carotid sinus pressor reflex. Subsequent administration of andromedotoxin, protoveratrine or neogermitrine, either into the carotid sinus adventitia or intravenously, fail to produce a depressor response. Veratridine injected into the carotid sinus adventitia during the hypotensive phase of one of the other drugs causes a sharp pronounced pressor response similar to surgical denervation of the sinus.

3. Veratridine administered intravenously to vagotomized dogs with intact carotid sinuses in doses sufficient to abolish the carotid sinus pressor reflex prevents the depressor action of intravenously injected andromedotoxin.

4. After denervation of the carotid sinuses in vagotomized dogs in which the carotid bodies are left intact (as determined by the hyperpneic response to intravenously administered sodium cyanide) veratridine, injected into the carotid sinus adventitia, is inactive.

5. It is concluded that drugs such as protoveratrine, neogermitrine and andromedotoxin cause a stimulation of the carotid pressoreceptors while veratridine produces a blockade of these receptors, after an initial transient stimulation.