EFFECT OF SYMPATHETIC DENERVATION ON THE ALPHA RECEPTORS OF THE CAT NICTITATING MEMBRANE

¹ Department of Pharmacology, McGill University, Montreal, Canada

The purpose of this investigation was to find out if sympathetic denervation of the cat nictitating membrane produced any change in the alpha receptors. The effect of alpha receptor adrenergic blocking agents on the response of the normal nictitating membrane to norepinephrine and to tyramine was compared with their effect on the response of the denervated and decentralized nictitating membrane to these agonists. The antagonism to norepinephrine by phenoxybenzamine and phentolamine was found to be less marked on the denervated and decentralized nictitating membrane than on the normal nictitating membrane. Both of these agents were found to potentiate the effect of tyramine on the chronically denervated nictitating membrane. Phenoxybenzamine blocked the response of the nictitating membrane to norepinephrine after cocaine or after chronic treatment of animals with reserpine. It blocked the effect of 5-hydroxytryptamine and of acetyicholine on the normal but not on the denervated nictitating membrane. It is concluded that sympathetic denervation of the cat nictitating membrane specifically affects the antagonistic effect of adrenergic blocking agents, possibly by producing a qualitative change in the receptors.