An α1-AR antagonist (Kis = 3.16, 1, and 3.98 nM for α1A-, α1B-, and α1D-ARs, respectively); inhibits norepinephrine-induced contractions in isolated rat aorta rings and human prostate strips (pA2s = 8.8 and 8.2, respectively); inhibits phenylephrine-induced increases in blood pressure and prostatic pressure in anesthetized dogs (pA2 = 7.5 for both)