A potent α1-AR antagonist (Ki = 0.229 nM in a radioligand binding assay); 3,800-fold selective for α1-ARs over α2-ARs (Ki = 871 nM); antagonizes norepinephrine-induced contraction of isolated rabbit aorta (pA2 = 10.11) but has no effect on contraction stimulated by histamine, serotonin, angiotensin II, or prostaglandin F2α; reverses the phenylephrine-induced pressor effect in pithed rats; reversibly reduces fertility in male rats when administered at a dose of 0.15 mg/kg; reduces prostatic pressure in a dose-dependent manner with minimal hypotensive effects in anesthetized dogs,