Pharmacological characterization of β-adrenoceptors mediating relaxation of the rat urinary bladder in vitro

1 Isoproterenol relaxed KCl-precontracted rat bladder strips with a pD(2) of 7.21 leaving a residual contractile response of 3.2% after 30 mu M. The selective beta(1)-agonist, T-0509 (pD(2):6.24, 10.1% residual contraction after 100 mu M), beta(2)-agonist, terbutaline (pD(2):5.43, 13.7% residual contraction after 100 mu M), and beta(3)-agonists, BRL 37344A (pD(2):6.60, 17.3% residual contraction after 100 mu M), and SR 58611A (pD(2):5.15, 34.0% residual contraction after 100 mu M), also relaxed bladder strips. 2 The relaxant response to isoproterenol was weakly but significantly antagonized by 1 mu M propranolol which produced a 3 fold shift of the concentration-response curve to the right, and significantly antagonized by the beta(1)-selective antagonist, metoprolol (10 mu M, 3 fold shift), and the beta(2)-selective antagonist, butoxamine (100 mu M, 6 fold shift). A combination of 10 mu M metoprolol and 100 mu M butoxamine caused a 15 fold shift of the concentration-response curve for isoproterenol to the right. Incubation with the beta(3)-antagonist, SR 59230A (1 mu M), caused a 6 fold shift of the concentration response curve for isoproterenol to the right. 3 The non-conventional partial agonist, CGP 12177A, weakly relaxed KCl-precontracted bladder strips (pD(2):3.31, 51.3% residual contraction after 300 mu M); the relaxation was resistant to blockade by 1 or 10 mu M propranolol. 4 In the presence of 200 mu M propranolol, CGP 12177A (20 mu M) or SR 59230A (10 mu M) antagonized surmountably the relaxant effects of BRL 37344A. 5 The data suggest that rat urinary bladder body contains beta(1), beta(2), and beta(3)-adrenoceptors, all of which mediate relaxation.