DEPRESSION OF THE VASOMOTOR CENTRE BY MECAMYLAMINE, INDEPENDENT OF ITS GANGLION-BLOCKING ACTIVITY.

Mecamylamine depressed the vasomotor centre independently of its ganglion-blocking action. The central action was elicited by small amounts of the drug when it was confined to the central nervous system of dogs and cats anaesthetized with pentobarbital sodium and of spinal cats. The spinal site of action was shown by the inhibition of vasomotor responses due to spinal compression in cats, when mecamylamine was introduced intrathecally in a dose too small to block autonomic ganglia. The supraspinal site of action was shown by intravertebral arterial injection of mecamylamine into cats, which caused hypotension and selectively blocked the electrically evoked pressor responses from the medulla without affecting the "nicotinic" ganglionic responses to acetylcholine. Injection of mecamylamine into the cerebral ventricles of dogs produced hypotension, and the reflex vasomotor responses to stimulation of afferent fibres in the vagus nerves and to occlusion of the common carotid arteries were inhibited without any change in the response of the nictitating membrane to preganglionic nervous stimulation.