.ALPHA.1-Adrenoceptor Subtype in the Rat Prostate Is Preferentially the .ALPHA.1A Type.
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α<SUB>1</SUB>-Adrenoceptors in the rat prostate were characterized by a binding assay using the newly synthesized radioligand [<SUP>3</SUP>H]-YM617 (5-[2-[[2[ethoxyring(n)-<SUP>3</SUP>H](<I>o</I>-ethoxyphenoxy)ethyl]amino] propyl]-2-methoxybenzenesulfonamide HCl) and an in vitro assay. Specific [<SUP>3</SUP>H]-YM617 binding in the rat prostate was saturable and of high affinity (K<SUB>D</SUB> = 61.5±5.9 pM) with 23.2±6.9 fmol/mg of protein as the maximal number of binding sites (B<SUB>max</SUB>). α-Adrenoceptor agonists and antagonists inhibited the binding of the radioligand with the following order of effectiveness: YM617 > prazosin = bunazosin > WB4101 >5-methyl-urapidil = phenoxybenzamine > phentolamine > <I>S</I>(+)-isomer of YM617 > yohimbine > norepinephrine > phenylephrine>methoxamine. α<SUB>1</SUB>-Adrenoceptors in the rat prostate preferred the <I>R</I>(-)-isomer of YM617 to the <I>S</I>(+)-isomer. Preincubation with chlorethylclonidine (CEC; 10<SUP>-5</SUP>M, 10 min) just slightly changed the B<SUB>max</SUB> value for [<SUP>3</SUP>H]-YM617 without changing the K<SUB>D</SUB> value in the prostate; however, CEC reduced the B<SUB>max</SUB> in the aorta. In the isolated tissue, pretreatment with CEC (10<SUP>-5</SUP>M, 10 and 30 min) time-dependently shifted to the right the dose-response curve for phenylephrine and decreased the maximal contraction of aortas induced by phenylephrine, but did not shift or decrease those of prostates. The present results indicate that the α<SUB>1</SUB>-adrenoceptors in the rat prostate are mainly CEC-insensitive (α<SUB>1A</SUB>), whereas those in the aorta are CEC-sensitive (α<SUB>1B</SUB>).
- 公益社団法人 日本薬理学会の論文
公益社団法人 日本薬理学会 | 論文
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