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

Abstract

Uridine adenosine tetraphosphate (Up ₄A), 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 A ₁ or A ₃ adenosine receptors (AR) results in vascular contraction via thromboxane (TX) A ₂ production. However, the mechanisms of Up ₄A-induced vascular contraction in mouse aorta are not understood. We hypothesize that Up ₄A-induced aortic contraction is through COX-derived TXA ₂ production, which requires activation of A ₁ and/or A ₃AR. Concentration responses to Up ₄A were conducted in isolated aorta. The TXB ₂ production, a metabolite of TXA ₂, was also measured. Up ₄A (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 ₄A-induced aortic contraction was blunted by both TX synthase inhibitor ozagrel and TXA ₂ receptor (TP) antagonist SQ29548. Surprisingly, A ₃AR deletion had no effect on Up ₄A-induced contraction. Moreover, A ₁AR deletion or antagonism as well as A ₁/A ₃AR deletion potentiated Up ₄A-induced aortic contraction, suggesting a vasodilator influence of A ₁AR. In contrast, non-selective purinergic P2 receptor antagonist PPADS significantly blunted Up ₄A-induced aortic contraction to a similar extent as selective P2X ₁R antagonist MRS2159, the latter of which was further reduced by addition of ozagrel. Endothelial denudation almost fully attenuated Up ₄A-induced contraction. Furthermore, Up ₄A (3 µM) increased TXB ₂ formation, which was inhibited by either MRS2159 or ozagrel. In conclusion, Up ₄A-induced aortic contraction depends on activation of TX synthase and TP, which partially requires the activation of P2X ₁R but not A ₁ or A ₃ AR through an endothelium-dependent mechanism.

Graphical Abstract