AGONIST-ANTAGONIST INTERACTIONS IN THE NORMAL AND SUPERSENSITIVE NICTITATING MEMBRANE OF THE SPINAL CAT

¹ Department of Pharmacology, West Virginia University Medical Center, Morgantown, West Virginia

"pA₂" values for norepinephrine/phentolamine and "pD’₂" values for norepinephrine/phenoxybenzamine were determined in vivo in the nictitating membrane of the spinal cat. Supersensitivity was produced by cocaine (5 mg/kg iv.), chronic denervation, chronic decentralization and reserpine (0.1 mg/kg daily for 14 days). Chlorisondamine (3.0 mg/kg) was administered to the spinal preparation to abolish tone. The "pA₂" values did not differ significantly from control in any of the groups studied. "pD’₂" values after cocaine were not significantly different from control. The "pD’₂" values, however, were decreased after denervation, decentralization and pretreatment with reserpine. These results suggest that: 1) the adrenergic receptor of the nictitating membrane is not altered or "deformed" in the types of supersensitivity studied, and 2) either the number of receptors increases or the relationship between receptor occupation and the response is altered (a change beyond the receptors) by denervation, decentralization and reserpine-treatment but not by cocainetreatment.