THE RELATION OF RETENTION OF NOREPINEPHRINE-H³ TO THE NOREPINEPHRINE CONTENT OF THE NICTITATING MEMBRANE OF THE SPINAL CAT DURING DEVELOPMENT OF DENERVATION SUPERSENSITIVITY

¹ Department of Pharmacology, Harvard Medical School, Boston, Massachusetts

The content of endogenous norepinephrine and the retention of exogenous norepinephrine -H³ in the nictitating membrane of the spinal cat were studied between the 16th and 48th hr after denervation and decentralization. The time interval between the intravenous injection of dl-norepinephrine-H³ and removal of the denervated nictitating membrane was 60 min. While decentralization failed to affect the endogenous norepinephrine stores, the norepinephrine content of the denervated nictitating membrane began to decline when the degeneration contraction developed. At its termination only 7.5% of the normal norepinephrine content was found. Decentralization failed to affect the retention of norepinephrine-H³. Nearly normal amounts of norepinephrine-H³ were recovered from the denervated nictitating membrane until the maximum of the degeneration contraction had passed. There was a sharp decline in norepinephrine-H³ thereafter. Cocaine (5 mg/kg i.v.) failed to affect the content of endogenous norepinephrine; it reduced the uptake of norepinephrine-H³ to one third of normal. It is concluded that denervation supersensitivity to norepinephrine has almost fully developed at a time when nearly normal amounts of norepinephrine-H³ are retained in the denervated nictitating membrane. The implications of these observations for the "uptake theory" of denervation supersensitivity are discussed.