Abstract
The relationship between the density of alpha sub(1)-adrenoceptors and the longitudinal contractile response of rat vas deferens was examined. The data suggest that only a portion of the alpha sub(1)-adrenoceptors in rat vas deferens affect longitudinal contraction. There is, however, a large pool of spare receptors for longitudinal contraction and these receptors are preferentially inactivated by application of phenoxybenzamine to the isolated tissue in an organ bath. When phenoxybenzamine is applied intravenously, the receptors affecting longitudinal contraction are inactivated to a degree similar to that of the total pool of receptors in this tissue.