Abstract

A quantitative comparison of the effects of hexamethonium and mecamylamine on ganglionic transmission was undertaken in order to investigate the mechanism of ganglionic blockade by mecamylamine.

A greater blockade of ganglionic transmission at a high frequency of stimulation than at a low frequency of stimulation was observed for mecamylamine and hexamethonium over a large part of the dose-response curve. Both drugs produced similar maximum blockade.

Waning of tension of the nictitating membrane with continued stimulation during partial ganglionic blockade was always observed with mecamylamine as well as with hexamethonium.

The dose-response curve for stimulation of the ganglion by intraarterial administration of acetylcholine was shifted to the right by a constant infusion of either hexamethonium or mecamylamine.

When hexamethonium, acetylcholine, or tetraethylammonium was injected simultaneously with a large dose of mecamylamine into the carotid artery, the total blocking effect on the superior cervical ganglion was less than the total blocking effect of the same dose of mecamylamine administered alone. The mechanism by which this antagonistic effect may occur is discussed.

The evidence presented supports the theory that the mechanism of action of mecamylamine on ganglionic transmission is similar to the mechanism of action of hexamethonium.