Ikunobu Muramatsu (1), Takanobu Taniguchi (1) and Kenichiro Okada (2)
Departments of (1) Pharmacology and (2) Urology, School of Medicine, Fukui Medical University, Matsuoka, Fukui 910-1193, Japan
Abstract: Selectivity of tamsulosin and terazosin to functional alpha1-adrenoceptors was examined. Both drugs competitively inhibited the contractile responses to noradrenaline in different tissues where the responses were mediated through the alpha1D-, alpha1B- or alpha1L-subtype. Together with the affinities obtained in the binding study with cloned (alpha1a, alpha1b, alpha1d) and native (alpha1A and alpha1B) subtypes, the selectivity of tamsulosin was alpha1A > alpha1L, alpha1D > alpha1B. Terazosin had lower affinity at various subtypes than tamsulosin, but showed relatively high selectivity to the alpha1D-subtype. In the human prostate, tamsulosin was more than 30-fold higher in affinity than terazosin in functional and binding studies.
Keywords: Tamsulosin, Terazosin, alpha1-Adrenoceptor