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

Isoproterenol relaxed KCl‐precontracted rat bladder strips with a pD 2 of 7.21 leaving a residual contractile response of 3.2% after 30 μ M . The selective β 1 ‐agonist, T‐0509 (pD 2  : 6.24, 10.1% residual contraction after 100 μ M ), β 2 ‐agonist, terbutaline (pD 2  : 5.43, 13.7% residual contraction after 100 μ M ), and β 3 ‐agonists, BRL 37344A (pD 2  : 6.60, 17.3% residual contraction after 100 μ M ), and SR 58611A (pD 2  : 5.15, 34.0% residual contraction after 100 μ M ), also relaxed bladder strips. The relaxant response to isoproterenol was weakly but significantly antagonized by 1 μ M propranolol which produced a 3 fold shift of the concentration‐response curve to the right, and significantly antagonized by the β 1 ‐selective antagonist, metoprolol (10 μ M , 3 fold shift), and the β 2 ‐selective antagonist, butoxamine (100 μ M , 6 fold shift). A combination of 10 μ M metoprolol and 100 μ M butoxamine caused a 15 fold shift of the concentration‐response curve for isoproterenol to the right. Incubation with the β 3 ‐antagonist, SR 59230A (1 μ M ), caused a 6 fold shift of the concentration response curve for isoproterenol to the right. The non‐conventional partial agonist, CGP 12177A, weakly relaxed KCl‐precontracted bladder strips (pD 2  : 3.31, 51.3% residual contraction after 300 μ M ); the relaxation was resistant to blockade by 1 or 10 μ M propranolol. In the presence of 200 μ M propranolol, CGP 12177A (20 μ M ) or SR 59230A (10 μ M ) antagonized surmountably the relaxant effects of BRL 37344A. The data suggest that rat urinary bladder body contains β 1 , β 2 , and β 3 ‐adrenoceptors, all of which mediate relaxation.British Journal of Pharmacology (1999) 127 , 1744–1750; doi: 10.1038/sj.bjp.0702709