Differential effects of diadenosine phosphates on purinoceptors in the rat isolated perfused kidney

1 The activation of various purinoceptors in rat renal vasculature by P-1,P-2-diadenosine pyrophosphate (Ap(2)A), P-1,P-3-diadenosine triphosphate (Ap(3)A), P-1,P-4-diadenosine tetraphosphate (Ap(4)A), P-1,P-5-diadenosine pentaphosphate (Ap(5)A), P-1,P-6-diadenosine hexaphosphate (Ap(6)A) was studied by measuring their effects of perfusion pressure of a rat isolated perfused kidney. 2 The vasoconstrictive response to Ap(5)A was completely due to P-2X purinoceptor activation, that to Ap(4)A and Ap(6) was P-2X purinoceptor mediated to a large extent, as evidenced by the inhibitory effects of suramin and pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid tetrasodium (PPADS). 3 The vasoconstrictive effects of Ap(2)A and Ap(3)A were mostly due to stimulation of A(1)-receptors, as shown by the inhibitory effect of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). 4 The vasoconstrictive response to Ap(6)A was partially insensitive to A(1) and P-2X purinoceptor blockers. 5 In raised tone preparations Ap(2)A and Ap(3)A evoked vasodilatation, which was blocked by the A(2) receptor blocker, 3,7-dimethyl-1-propargylxanthine (DMPX). 6 In raised tone preparations Ap(4)A evoked vasodilatation when the P-2-purinoceptors were blocked by suramin. 7 The activation of different purinoceptor subtypes by diadenosine phosphates critically depends on the number of phosphate groups.