Abstract

The effects of alpha and beta adrenergic agonists and antagonists on isolated smooth muscle preparations from the rabbit bladder body, bladder base and proximal urethra have been studied. The predominance of alpha receptors in the proximal urethra and the bladder base was observed via contraction of these areas by norepinephrine and blockade by phentolamine. Alpha receptor-mediated contractile activity could be unmasked in the bladder body when beta receptors were blocked with propranolol. Isoproterenol, 1 X 10(-10) to 3 X 10(-7) M, had a strong, dose-related relaxant effect on the bladder body, but little effect on the bladder base or proximal urethra. Selective beta-2 agonists such as terbutaline, salbutamol and ritodrine elicited tissue responses similar to those of isoproterenol. The pD2 values for isoproterenol, terbutaline, salbutamol and ritodrine were 8.59, 7.87, 7.34, and 6.52, respectively. Dobutamine, a selective beta-1 agonist, failed to cause significant relaxation of these tissues. The nonselective beta receptor blocker, propranolol, and the selective beta-2 receptor blocker, butoxamine, competitively antagonized the relaxant effects of the four active beta agonists; however, atenolol, a selective beta-1 receptor blocker, was inactive. On the basis of the selective action of these agonists and antagonists, we concluded that beta-2 receptors mediate relaxation of the vesicourethral smooth muscles of the rabbit and the participation of beta-1 receptors in the areas is insignificant.