In vivo effects of diadenosine polyphosphates on rat renal microcirculation

BACKGROUND: Diadenosine polyphosphates (APXA) are vasoactive nucleotides that elicit effects via purinoceptors. Recent data suggest differential effects of APXA on kidney vasculature. METHODS: The in vivo effects of AP3A, AP5A, and adenosine on renal microvessels and the role of purinoceptors were investigated by the application of agonists to the hydronephrotic rat kidney and preincubation with respective antagonists. RESULTS: The addition of the agonists (10-7 mol/L up to 10-4 mol/L) resulted in a concentration-dependent transient vasoconstriction [interlobular artery (ILOB): adenosine 30 +/- 7%, N = 7, AP3A 35 +/- 10%, N = 5; AP5A 66 +/- 19%, N = 5; 10-5 mol/L each] lasting up to one minute, followed by a concentration-dependent vasodilation (ILOB: adenosine 10 +/- 3%, N = 6; AP3A 19 +/- 4%, N = 5; AP5A 12 +/- 5%, N = 6; 10-5 mol/L each). In ILOB and in the afferent arteriole (AFF), the constrictory effects of AP5A were more pronounced than those of AP3A and adenosine. In the efferent arteriole (EFF), vascular tone was only slightly affected by all agonists. The dilatory potency was comparable for all agonists in ILOB and EFF. No significant vasodilation occurred in AFF. The application of the selective A1 receptor antagonist DPCPX (10-5 mol/L) completely abolished the adenosine-induced vasoconstriction, whereas the A2 receptor antagonist DMPX and the P2 purinoceptor antagonists PPADS and A3P5P (all 10-5 mol/L) did not affect adenosine-induced constriction. The AP3A-induced constriction was abolished by DPCPX and was partially inhibited by PPADS. The constriction induced by AP5A was less sensitive to DPCPX but more sensitive to PPADS. In ILOB and EFF, DMPX or A3P5P abolished dilation after the addition of the agonists. The dilation after AP5A was not significantly reduced. In AFF, no significant dilation was observed with these agonists alone, but it was clearly visible in the presence of DPCPX or PPADS. CONCLUSIONS: APXA evoke transient constrictions in vessels of the hydronephrotic rat kidney, which are mediated by A1 and P2 purinoceptors. The length of the phosphate chain determines the degree of vasoconstriction and the extent to which the substances exert effects on the P2 purinoceptor subtypes. ILOB and AFF are more potently affected by APXA than EFF. Afferent vasodilation is partially overridden by sustained vasoconstriction.