L-771688 hydrochloride is a potent and highly selective α1A-adrenoceptor antagonist (Kd=43-90 pM). L-771688 hydrochloride is effective against cloned human, rat and dog α1A-adrenergic receptors. L-771688 exhibits high affinity (Ki ≤ 1 nM) and over 500-fold selectivity over the α1B and α1D isoforms. L-771688 potently antagonizes norepinephrine-induced responses at these receptors. Inhibits contractions induced by phenylephrine or A-61603 in rat, dog, human and monkey models.