A comparison of the antagonistic activities of tamsulosin and terazosin against human vascular alpha(1)-adrenoceptors

Tamsulosin, a selective alpha(1A)-adrenoceptor antagonist, and terazosin, a non-selective one, are effective for the treatment of urinary disturbance due to benign prostatic hypertrophy. In the present study, their al-adrenoc eptor-blocking effects on blood vessels, which may cause orthostatic hypote nsion, were investigated in 10 healthy males. After the subjects took orall y 0.2 mg of tamsulosin, 1 mg of terazosin or a lactate capsule as the contr ol in a randomized cross-over fashion, their finger tip vasoconstrictor res ponse to cold stimulation and vasoconstrictor response of the dorsal hand v ein to increasing doses of phenylephrine were examined. The finger tip vaso constrictor response was significantly reduced and the infusion rate of phe nylephrine producing a half-maximal constriction was significantly increase d by terazosin, but tamsulosin had no significant effect on these parameter s. These data suggest that the usual dose of tamsulosin exerts little alpha (1)-adrenoceptor-blocking activity on blood vessels, and orthostatic episod es might be mild, if any, during the treatment with tamsulosin.