CATECHOLAMINE CONTENT OF THE CAT NICTITATING MEMBRANE FOLLOWING PROCEDURES SENSITIZING IT TO NOREPINEPHRINE

¹ Department of Pharmacology, State University of New York Downstate Medical Center, Brooklyn, N. Y.

The effect of denervation, decentralization and reserpinization on the catecholamine content (norepinephrine and epinephrine) and sensitivity of the smooth muscles of the nictitating membrane of the cat was Studied. Catecholamine content of superior cervical ganglia was also determined following decentralization and reserpinization.

The predominant catecholamine in nictitating membrane and superior cervical ganglion was norepinephrine. Epinephrine concentration was only a few per cent of that of norepinephrine in both tissues.

A precipitous fall of about 95% in catecholamine content of the nictitating membrane occurred between the twenty-fourth and thirty-sixth hour after removal of time superior cervical ganglion. Two weeks after denervation the content was essentially zero and no recovery was observed up to 105 days. Denervation increased sensitivity of the membrane to exogenous norepinephrine 200- to 300-fold.

Reserpine (1 mg/kg intraperitoneally) reduced norepinephrine content of the nictitating membrane by about 98% within 24 hours after injection and increased sensitivity to norepinephrine only about 2-fold. Essentially full recovery of norepinephrine content was observed 21 days after treatment.

Decentralization did not affect the norepinephrime content of nictitating membranes but increased sensitivity to norepinephrine 10- to 15-fold. Decentralization appeared to increase the norepinephrine content of superior cervical ganglia. Decentralization did not appreciably interfere with either the depletion of catecholamine stores by reserpine in membranes or ganglia, or the time for recovery of such stores following treatment with reserpine.

Certain current hypotheses concerning the cause of supersensitivity in the nictitating membrane are discussed in relation to the data obtained in this study, and none appears to be completely satisfactory. An hypothesis is put forward based on the concept that normal post-ganglionic adrenergic nerve terminals possess a very efficient mechanism for removing norepinephrine, and thus limit the concentration of this substance reaching adrenergic receptors of effector cells. It is proposed that binding of norepinephrine at specific sites is tile initial step in this removal mechanism.