Effects of four different .ALPHA.1-adrenoceptor antagonists on .ALPHA.-adrenoceptor agonist-induced contractions in isolated mouse and hamster ureters

Abstract

To compare the efficacy of the selective alpha(1A)-adrenoceptor antagonist silodosin with those of doxazosin, terazosin, and alfuzosin against alpha-adrenoceptor agonist-induced contractions in mouse and hamster ureters. The four alpha(1)-adrenoceptor antagonists were evaluated against norepinephrine-induced phasic contractions in mouse isolated ureteral preparations and against phenylephrine-induced sustained contractions in hamster isolated ureteral preparations using a functional experimental technique. In mouse ureters, silodosin (a selective alpha(1A)-adrenoceptor antagonist), doxazosin (a nonselective alpha(1)-adrenoceptor antagonist), terazosin (a nonselective alpha(1)-adrenoceptor antagonist), and alfuzosin (a nonselective alpha(1)-adrenoceptor antagonist) all shifted the norepinephrine concentration-response curve to the right. The rank order of potencies (pK(B) value) was silodosin (9.47 +/- 0.16) > doxazosin (8.62 +/- 0.15) > terazosin (8.39 +/- 0.16) > alfuzosin (8.03 +/- 0.12). In hamster ureters, all four antagonists shifted the phenylephrine concentration-response curve to the right, the rank order of potencies being silodosin (10.09 +/- 0.13) > doxazosin (8.22 +/- 0.16) > terazosin (7.75 +/- 0.15) > alfuzosin (7.70 +/- 0.10). In each case, silodosin was much more potent than the other three drugs. In this study, silodosin suppressed both mouse and hamster ureteral contractions more potently than doxazosin, terazosin, or alfuzosin. Hence, this alpha(1A)-adrenoceptor antagonist warrants further study as a potentially very useful medication for stone passage in urolithiasis patients.