Subtype-selective α1A-adrenoceptor antagonist that displays > 600-fold selectivity over other adrenoceptors (Kivalues are 0.35, 220, 370, 540, 800 and 1200 nM for α1A, α1B, α2C, α1D, α2B and α2A subtypes respectively and 540 nM for L-type Ca2+ channels). Inhibits noradrenalin-induced contractions in rabbit vascular and lower urinary tissues.