Vasoconstrictor and vasodilator responses to various agonists in the rat perfused mesenteric arterial bed: selective inhibition by PPADS of contractions mediated via P_2x‐purinoceptors

Abstract

1The effect of pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on vasoconstrictor and/or vasodilator responses to various agonists and electrical field stimulation was investigated in the rat mesenteric arterial bed at basal tone and at tone raised by methoxamine (15-501M).2 At basal tone, nucleotides produced vasoconstriction with the following rank order of potency: a,-methylene ATP>>2-methylthio ATP> ATP= UTP. PPADS (0.3-10 tM) concentrationdependently antagonized ,-methylene ATP-, 2-methylthio ATP-and ATP-induced responses. UTP-, noradrenaline-and nerve-mediated (4-32 Hz) increases in perfusion pressure remained unaffected by 10 M PPADS. 3 In raised tone preparations, nucleotides produced vasodilations, their rank order of potency being 2-methylthio ATP>ATP>UTP. Responses to 2-methylthio ATP were slightly antagonized, whereas ATP-and UTP-induced responses remained unaffected by 1OpiM PPADS. In addition, acetylcholineand adenosine-elicited relaxations were not influenced by 10WpM PPADS.4 The present results confirm the previously described selective P2X antagonism by PPADS, this compound being ineffective at muscarinic M3-and adenosine PI-receptors as well as at al-adrenoceptors.There was some inhibition of P2y-purinoceptors but at a much higher concentration than required for inhibition of P2h-purinoceptors.5 In addition, this study provides evidence for the ineffectiveness of PPADS at both vasoconstrictionand vasodilatation-mediating P2u-purinoceptors.

Relative contribution of P2U‐ and P2Y‐purinoceptors to endothelium‐dependent vasodilatation in the golden hamster isolated mesenteric arterial bed

“…Our (Windscheif et al, 1994), to inhibit P2Y-purinoceptor stimulated phospholipase C activity in turkey erythrocytes (Boyer et al, 1994) and to inhibit P2y-but not P2u-mediated accumulation of total [3H]-inositol (poly)phosphates in bovine aortic endothelial cells (Brown et al, 1995). Further, our results with PPADS suggest that the poor efficacy of 2MeSATP was not due to an opposing constrictor action at P2X-purinoceptors since vasodilatation was not augmented.…”

“…For example, in rabbit mesenteric arteries P2Y receptors are present on the smooth muscle (Mathieson & Burnstock, 1985), whereas in rat mesenteric arteries P2y receptors are located on the endothelium, where they appear to coexist with P2u receptors (Ralevic & Burnstock, 1988;Windscheif et al, 1994). The aim of the current study.…”

“…The trypanoBritish Journal of Pharmacology (1996) 117,[1797][1798][1799][1800][1801][1802] side suramin is a non-selective antagonist of P2-purinoceptors (Dunn & Blakeley, 1988;Hoyle et al, 1990;Leff et al, 1990). Arylazidoaminopropionyl ATP (Hogaboom et al, 1980;Fedan et al, 1981) and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (Lambrecht et al, 1992;Ziganshin et al, 1994;Windscheif et al, 1994) are relatively selective P2X-purinoceptor antagonists in some tissues. The suramin analogue NF023 has recently been shown to be P2x-receptor selective in the rabbit vas deferens (Ziyal et al, 1994) and in rat and hamster mesenteric arteries (Ziyal et al, 1995).…”

Inhibition of ecto‐ATPase by PPADS, suramin and reactive blue in endothelial cells, C6 glioma cells and RAW 264.7 macrophages

“…This finding is consistent with the high levels of ectoATPase present in the artery biophase which could thus efficiently hydrolyse agonists that are enzyme substrates (Gordon et al, 1989). PPADS, in the concentration-range of 0.3-10 IOM, has been described as a selective antagonist of P2X purinoceptors in various preparations (Lambrecht et al, 1992;Ziganshin et al, 1993;Windscheif et al, 1994). However, PPADS has also been reported to antagonize P2Y-mediated responses with different potencies.…”

PPADS: an antagonist at endothelial P2Y‐purinoceptors but not P2U‐purinoceptors

“…For example Windscheif et al (1994) show that while P2X-purinoceptor-mediated vasomotor responses of the rat mesentery were potently antagonized by PPADS, there were only weak antagonistic effects on P2y-and no effect on P2U-purinoceptor-mediated responses. They conclude, therefore, that PPADS can be used as a selective antagonist in this preparation.…”