α_1-Adrenoceptors in the Guinea Pig Thoracic Aorta

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In the present study, we tried to determine which α_1-adrenoceptor subtypes are involved in the guinea pig thoracic aorta by using in vitro functional analysis. In first, we tried to estimate the pA_2 values of some key α_1-adrenoceptor antagonists(prazosin, 5-methyl-urapidil, WB4101, BMY7378 and tamsulosin)against responses to norepinephrine in the thoracic aorta of guinea pigs. The concentration-response curves of norepinephrine were rightward shifted by the presence of prazosin, 5-methylurapidil, WB4101, BMY7378 and tamsulosin. The pA_2 values for these antagonists against norepinephrine were 7.83, 7.78, 8.20, 5.73 and 9.57, respectively. In second, we tried to compare the estimated pA_2 values obtained in the present study with reported pKi and pA_2 values for cloned and native α_1-adrenoceptor subtypes. In rabbit mesenteric artery, trigone, urethra, prostate and human lower urinary tract which were proposed to contain the putative α_<1L>-adenoceptor, we obtained the good correlation for the pA_2 values reported in these tissues with pA_2 values estimated in guinea pig thoracic aorta. Moreover, regression lines were close to the line of identity. These results suggest that the α_1-adenoceptors mediating contraction of guinea pig thoracic aorta are similar pharmacologically to the putative α_<1L>-adenoceptor subtype in rabbit mesenteric artery, trigone, urethra, prostate and human lower urinary tract. As a final point, guinea pig thoracic aorta may be able to use as a tool to develop the new α_1-adrenoceptor antagonist which is therapeutically advantageous in the treatment of urinary tract obstruction(e.g., in benign prostatic hyperplasia).
日本平滑筋学会の論文

α_1-Adrenoceptors in the Guinea Pig Thoracic Aorta

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