Selective, high affinity, non-competitive α1A adrenoceptor antagonist (Ki = 0.35 nM). Exhibits no significant activity against a range of other GPCRs, including α2A, β1 and β2 adrenoceptors. Antagonizes effects of phenylephrine (Cat. No. 2838) on isolated rabbit prostate muscle in vitro and on intra-urethral pressure in rats. MW (observed): 7283.22.