α_1-Adrenoceptor Subtypes and α_1-Adrenoceptor Antagonists

α_1-adrenoceptors are widely distributed in the human body and play important physiologic roles. Three α_1-adrenoceptor subtypes (α_<1A>, α_<1B> and α_<1D>) have been cloned and show different pharmacologic profiles. In addition, a putative α_1-adrenoceptor (α_<1L> subtype) has also been proposed. Recently, three drugs (tamsulosin, naftopidil, and silodosin) have been developed in Japan for the treatment of urinary obstruction in patients with benign prostatic hyperplasia. In this review, we describe recent α_1-adrenoceptor subclassifications and the pharmacologic characteristics (subtype selectivity and clinical relevance) of α_1-adrenoceptor antagonists.