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

摘要

Uridine adenosine tetraphosphate (Up4A), a novel endothelium-derived vasoactive agent, is proposed to play a role in cardiovascular disorders and induces aortic contraction through activation of cyclooxygenases (COX). We and others demonstrated that activation of A1 or A3 adenosine receptors (AR) results in vascular contraction via thromboxane (TX) A2 production. However, the mechanisms of Up4A-induced vascular contraction in mouse aorta are not understood. We hypothesize that Up4A-induced aortic contraction is through COX-derived TXA2 production, which requires activation of A1 and/or A3AR. Concentration responses to Up4A were conducted in isolated aorta. The TXB2 production, a metabolite of TXA2, was also measured. Up4A (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, Up4A-induced aortic contraction was blunted by both TX synthase inhibitor ozagrel and TXA2 receptor (TP) antagonist SQ29548. Surprisingly, A3AR deletion had no effect on Up₄A-induced contraction. Moreover, A₁AR deletion or antagonism as well as A₁/A₃AR deletion potentiated Up₄A-induced aortic contraction, suggesting a vasodilator influence of A₁AR. In contrast, non-selective purinergic P2 receptor antagonist PPADS significantly blunted Up₄A-induced aortic contraction to a similar extent as selective P2X₁R antagonist MRS2159, the latter of which was further reduced by addition of ozagrel. Endothelial denudation almost fully attenuated Up₄A-induced contraction. Furthermore, Up₄A (3 µM) increased TXB₂ formation, which was inhibited by either MRS2159 or ozagrel. In conclusion, Up₄A-induced aortic contraction depends on activation of TX synthase and TP, which partially requires the activation of P2X₁R but not A₁ or A₃ AR through an endothelium-dependent mechanism.