ON THE SPECIFICITY OF ALPHA ADRENERGIC RECEPTOR LABELING BY ¹⁴C-DIBENAMINE

¹ Department of Pharmacology, University of Illinois at the Medical Center, Chicago, Illinois

Affinity-labeling experiments with ¹⁴C-Dibenamine have been performed on strips of stomach muscularis and aorta (intima-media) from the rabbit. The percentage of alpha adrenergic receptors theoretically alkylated was calculated and correlated with the radioactivity present in the strips. The results indicate that the specificity of alpha receptor labeling in intima-media decreases when procedures which alkylate greater proportions of the receptors are employed. This relationship is not evident in stomach muscularis where lower concentrations of Dibenamine are effective. Pretreatment of strips of intimamedia with mechlorethamine, a less specific alkylating agent, does not appear to increase the specificity of subsequent receptor labeling by ¹⁴C-Dibenamine. Our estimate, which is undoubtedly high, is that there are 1 to 5 x 10¹² alpha adrenergic receptors per mg of tissue dry weight in these tissues.