Kazuhiro Harada, Masami Ohmori, Yasuhiko Kitoh, Koh-ichi Sugimoto and
Akio Fujimura
Department of Clinical Pharmacology, Jichi Medical School, Minamikawachi-machi,
Tochigi 329-0498, Japan
Abstract: Tamsulosin, a selective alpha1A-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 alpha1-adrenoceptor-blocking effects on blood vessels,
which may cause orthostatic hypotension, were investigated in 10 healthy
males. After the subjects took orally 0.2 mg of tamsulosin, 1 mg of terazosin
or a lactate capsule as the control in a randomized cross-over fashion,
their finger tip vasoconstrictor response to cold stimulation and vasoconstrictor
response of the dorsal hand vein to increasing doses of phenylephrine were
examined. The finger tip vasoconstrictor response was significantly reduced
and the infusion rate of phenylephrine producing a half-maximal constriction
was significantly increased by terazosin, but tamsulosin had no significant
effect on these parameters. These data suggest that the usual dose of tamsulosin
exerts little alpha1-adrenoceptor-blocking activity on blood
vessels, and orthostatic episodes might be mild, if any, during the treatment
with tamsulosin.
Keywords: Tamsulosin, Terazosin, alpha1-Adrenoceptor, Blood
vessel, Human study