INFLUENCE OF TYRAMINE ON RECEPTOR INTERACTION WITH DIBENAMINE IN AORTIC STRIPS FROM RESERPINE-TREATED RABBITS

¹ Department of Pharmacology, Medical Units, University of Tennessee, Memphis, Tennessee

The object of this study was to investigate the direct action of various concentrations of tyramine on epinephrine receptors located in aortic strips from 24- and 48-hr reserpine-pretreated rabbits. The protection technique (Furchgott and Bhadrakom, 1953) was utilized. Tyramine-HCl, 5 x 10^-5 and 10^-4 g/ml, partially protected epinephrine receptors from Dibenamine blockade, a direct effect. Tyramine 10^-7 produced no alteration of Dibenamine blockade, but tyramine 10^-8, a low concentration, increased rather than decreased Dibenamine blockade. The hypothesis is presented that this potentiation is a manifestation of a decrease in the effectiveness of the diffusion barrier between the receptor and the biophase. Data obtained from cocaine-tyramine protection experiments show potentiation of Dibenamine blockade, which seems to be the result of an action of cocaine on the receptor site. A reasonable explanation of this effect is that a receptor transfer site sensitive to cocaine is located within the diffusion barrier and is similar to the storage area transfer system suggested by Furchgott et at. (1963). It was also noted that strips from 24- and 48-hr reserpine-pretreated rabbits do not possess statistically different sensitivities to epinephrine. However, they do show an increase in the maximal response when compared with responses of strips from rabbits not treated with reserpine.