TY - JOUR T1 - Influence of Purinoceptor Antagonism on Diadenosine Pentaphosphate-Induced Hypotension in Anesthetized Rats JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 963 LP - 968 VL - 294 IS - 3 AU - Martin Steinmetz AU - Truc Van Le AU - Peter Hollah AU - Gert Gabriëls AU - Helge Hohage AU - Karl Heinz Rahn AU - Eberhard Schlatter Y1 - 2000/09/01 UR - http://jpet.aspetjournals.org/content/294/3/963.abstract N2 - Diadenosine polyphosphates (ApnA; n = 3–6) are potent vasoactive agents in isolated vessels. Information on effects of ApnA in vivo is still limited despite the fact that these compounds are starting to be used in humans. This study was designed to compare the effects of ApnA and their possible metabolites on blood pressure in vivo and to functionally identify purinoceptors involved in their action. All four ApnA and their degradation products induced a sustained drop of mean arterial blood pressure during i.v. infusion, which was fully reversible. The rank order of potency was Ap4A ≥ Ap6A > Ap5A = Ap3A = ATP = ADP > AMP ≥ adenosine, suggesting that the hypotensive effect is predominantly evoked by the original dinucleotides and not by their degradation products. The hypotensive effect of Ap5A was reduced by the P2X and P2Y1 purinoceptor antagonist pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonic acid, the A1 purinoceptor antagonist 8-cyclopentyl-1,3-dipropylxanthine, and the A2 purinoceptor antagonist 3,7-dimethyl-1-propargylxanthine. The hypertensive effect by the prototype P2X receptor agonist αβ-methylene ATP was inhibited by pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonic acid, too. Purinoceptor antagonists reduced the maximal effects of the agonists indicating a noncompetitive inhibition. In summary, the reported vasocontractile effect of ApnA seems to be limited to isolated preparations under resting tone conditions; however, the systemic cardiovascular effects of all four ApnA are hypotensive, also making them candidates for blood pressure reduction in humans. These effects are fast in onset and easily reversible. Activation of different purinoceptors in the vasculature (most probably P2Y1 and A2 receptors) contributes to the Ap5A-induced decrease of mean arterial blood pressure. The American Society for Pharmacology and Experimental Therapeutics ER -