Role of the beta(3)-adrenoceptor in urine storage in the rat: comparison between the selective beta(3)-adrenoceptor agonist, CL316, 243, and various smooth muscle relaxants.

The objective of this study was to compare the effects of a beta(3)-adrenoceptor (beta(3)-AR) agonist on bladder function and cardiovascular parameters in rats with those of several drugs that act on smooth muscle. CL316,243 (beta(3)-AR agonist), isoproterenol (nonselective beta-AR agonist), procaterol (beta(2)-AR agonist), verapamil (Ca(2+) antagonist), and papaverine (antispastic drug) each evoked a concentration-dependent relaxation of the detrusor in vitro. They also reduced bladder pressure in anesthetized rats, the beta-AR agonists apparently being more potent than the other drugs. Atropine (muscarinic antagonist) neither relaxed detrusor strips nor reduced bladder pressure. In anesthetized rats, CL316,243 and atropine each had only a slight influence on blood pressure and heart rate, but isoproterenol, procaterol, verapamil, and papaverine significantly affected cardiovascular function at the same dose range as that required to reduce bladder pressure. In cystometry experiments, CL316,243 (10 microg/kg i.v.), verapamil (1 mg/kg i.v.), and papaverine (1 mg/kg i.v.) all significantly prolonged micturition interval and increased bladder capacity, but did not change the residual urine volume after a micturition contraction. Procaterol (100 microg/kg i.v.) prolonged the micturition interval and increased both bladder capacity and residual urine volume (all significantly). Atropine (100 microg/kg i.v.) reduced micturition pressure and increased residual urine volume (both significantly). Because the human detrusor, like the rat detrusor, relaxes on beta(3)-AR stimulation, we conclude that this beta(3)-AR agonist may have potential in pollakiuria (frequent urination) as a therapeutic agent without cardiovascular side effects.