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      Effects of 2-[(5-Chloro-2-methoxyphenyl)azo]-1H-imidazole (M6434), a New α-Adrenoceptor Agonist, on Pre- and Postsynaptic α-Adrenoceptors in Canine Mesenteric Artery

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          Post- and presynaptic α-adrenoceptors in the canine mesenteric artery show distinct features of α<sub>1</sub> and α<sub>2</sub> types, respectively. The effects of a newly synthesized pressor agent, 2-[(5-chloro-2-methoxyphenyl)azo]-1H-imidazole (M6434), on the pre- and postsynaptic α-adrenoceptors of the canine mesenteric artery were examined pharmacologically. M6434 produced a contractile response in the mesenteric artery. The EC<sub>5</sub>o value of M6434 was 1.1 × 10<sup>–7</sup> M, that was almost the same as that of norepinephrine but significantly lower than the value seen with methoxamine. The maximum amplitude of contraction developed by M6434 was approximately 81 % of that induced by norepinephrine. The contractile response to M6434 was competitively inhibited by prazosin (pA<sub>2</sub> = 9.23 ± 0.08) and yohimbine (pA<sub>2</sub> = 7.85 ± 0.09). M6434 also reduced the <sup>3</sup>H-efflux evoked by electrical transmural stimulation in the arterial tissues preincubated with <sup>3</sup>H-norepinephrine, and the maximum inhibition corresponded to about 60 % of the case of norepinephrine. This presynaptic effect was inhibited by yohimbine but not by prazosin. The results show that M6434 is almost a full agonist for α<sub>1</sub>-adrenoceptor with partial α<sub>2</sub>-effect.

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          Author and article information

          J Vasc Res
          Journal of Vascular Research
          S. Karger AG
          23 September 2008
          : 21
          : 5
          : 246-251
          Department of Pharmacology, Faculty of Medicine, Kyoto University, Japan
          158517 Blood Vessels 1984;21:246–251
          © 1984 S. Karger AG, Basel

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          Pages: 6
          Research Paper


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