A Comparison of the Antagonistic Activities of Tamsulosin and Terazosin Against Human Vascular α1Adrenoceptors

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.

Stimulatory effect of caffeic acid on α 1A -adrenoceptors to increase glucose uptake into cultured C 2 C 12 cells

“…Minneman et al (1988) identified two subtypes of α 1 -adrenoceptors, using WB 4101 and CEC. In the present study, actions of caffeic acid and phenylephrine were blocked in parallel by the pretreatment with α 1A -adrenoceptor antagonists, both WB 4101 (Minneman et al 1988) and tamsulosin (Harada et al 1999), but not by CEC, an antagonist of α 1B -adrenoceptors (Minneman et al 1988). Activation of α 1A -adrenoceptor in C 2 C 12 cells by caffeic acid to enhance glucose uptake can thus be considered.…”

Critical Role for the α-1B Adrenergic Receptor at the Sympathetic Neuroeffector Junction

“…In contrast, tamsulosin, an ␣ 1A AR selective antagonist, is not associated with a greater incidence of OI than placebo. 20,21 Thus, although the ␣ 1A and ␣ 1D AR may play a role in blood pressure regulation, the ␣ 1B AR is likely critical in mediating acute vascular responses to postural redistribution of blood volume. Although all ␣ 1B AR subtypes are variably expressed in the heart, studies investigating their role in myocardial contractility and structure have yielded variable results that are species, age, and model dependent.…”

α₁-Blocker Therapy for Lower Urinary Tract Symptoms Suggestive of Benign Prostatic Obstruction: What Are the Relevant Differences in Randomised Controlled Trials?

“…This suggests that 0.2 mg tamsulosin has little – if any – cardiovascular effect in contrast to 1 mg doxazosin [150]. A subsequent study with the same methods confirmed similar differentiation between 0.2 mg tamsulosin and 1 mg terazosin [151]. …”