Mechanisms underlying uridine adenosine tetraphosphate-induced vascular contraction in mouse aorta: Role of thromboxane and purinergic receptors

Uridine adenosine tetraphosphate (Up(4)A), a novel endothelium-derived vasoactive agent, is proposed to play a role in cardiovascular disorders and induces aortic contraction through activation of cyclooxygenases (COXs). We and others demonstrated that activation of A(1) or A(3) adenosine receptors (ARs) results in vascular contraction via thromboxane (TX) A(2) production. However, the mechanisms of Up(4)A-induced vascular contraction in mouse aorta are not understood. We hypothesize that Up(4)A-induced aortic contraction is through COX-derived TXA(2) production, which requires activation of A(1) and/or A(3)AR. Concentration responses to Up(4)A were conducted in isolated aorta. The TXB2 production, a metabolite of TXA(2), was also measured. Up(4)A (10(-9)-10(-5) M) produced a concentration-dependent contraction > 70%, which was markedly attenuated by COX and COX1 but not by COX2 inhibition. Notably, Up(4)A-induced aortic contraction was blunted by both TX synthase inhibitor ozagrel and TXA(2) receptor (TP) antagonist SQ29548. Surprisingly, A(3)AR deletion had no effect on Up(4)A-induced contraction. Moreover, A(1)AR deletion or antagonism as well as A(1)/A(3)AR deletion potentiated Up(4)A-induced aortic contraction, suggesting a vasodilator influence of A(1)AR. In contrast, non-selective purinergic P2 receptor antagonist PPADS significantly blunted Up(4)A-induced aortic contraction to a similar extent as selective P2X(1)R antagonist MRS2159, the latter of which was further reduced by addition of ozagrel. Endothelial denudation almost fully attenuated Up(4)A-induced contraction. Furthermore, Up(4)A (3 mu M) increased TXB2 formation, which was inhibited by either MRS2159 or ozagrel. In conclusion, Up(4)A-induced aortic contraction depends on activation of TX synthase and TP, which partially requires the activation of P2X(1)R but not A(1) or A(3)AR through an endothelium-dependent mechanism. (C) 2015 Elsevier Inc. All rights reserved.