Kazumasa Shinozuka*, Yoshie Tanioka, Young Mi Kwon, Naoko Tanaka, Yoko
Kubota, Kazuki Nakamura and Masaru Kunitomo
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Mukogawa
Women's University, 11-68, Koshien Kyuban-cho, Nishinomiya 663-8179, Japan
*Corresponding author. Fax: +81-798-45-9944
E-mail: kazumasa@mwu.mukogawa-u.ac.jp
Abstract: The effects of purinoceptor agonists on noradrenaline NA
release by electrical stimulation in rat mesenteric arteries were examined
to clarify the pharmacological properties of prejunctional purinoceptors
on adrenergic nerves. Adenosine and the other P1-receptor agonists,
5'-(N-ethylcarboxamido) adenosine and 2-chloroadenosine, significantly
inhibited the release of NA. Also b,g-methylene
ATP and 2-methylthio ATP, P2-receptor agonists, significantly
inhibited NA releases. The inhibitory effect of adenosine was significantly
reduced by adenosine deaminase, but those of b,g-methylene
ATP and 2-methylthio ATP were not affected. This suggests that the inhibitory
effects of P2-receptor agonists are not due to conversion into
adenosine. 1,3-Dipropyl-8-cyclopentylxanthine (DPCPX), a P1 (A1)-receptor
antagonist, significantly reduced the inhibitory effects of not only the
P1- but also P2-receptor agonists. Therefore, DPCPX
appears to act on both prejunctional P1- and P2-receptor
as an antagonist. Pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS),
a P2-receptor antagonist, significantly reduced the inhibitory
effects of the P2-receptor agonists, but not those of the P1-receptor
agonists. From these findings in the rat mesenteric artery, the P1-receptor
agonist-induced inhibition of NA-release appears to be mediated via a well-known
prejunctional P1-receptor of the A1-subtype, but the
P2-receptor agonist-induced inhibition appears to be mediated
via an unidentified purinoceptor that is blocked not only by P2-receptor
antagonists but also by P1-receptor antagonists.
Keywords: ATP, Adenosine, Rat mesenteric artery, Noradrenaline release,
Prejunctional inhibitory purinoceptor
Copyright The Japanese Pharmacological Society
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