The role of prostaglandin E and thromboxane-prostanoid receptors in the response to prostaglandin E2 in the aorta of Wistar Kyoto rats and spontaneously hypertensive rats

Aims The present study examined the hypothesis that prostaglandin E-2 (PGE(2)) through activation of prostaglandin E (EP) receptor contributes to endothelium-dependent contractions. Methods and results Western blotting revealed that the protein expression of EP1 receptor was significantly down-regulated in the aorta of the spontaneously hypertensive rat (SHR), but there was no significant difference in the expression of EP2, EP4, and total EP3 receptors between preparations of Wistar Kyoto rats (WKY) and SHR. Isometric tension studies showed that low concentrations of PGE(2) caused endothelium-dependent relaxations in WKY but not in aortas of the SHR. High concentrations of PGE(2) evoked contractions predominately through the activation of thromboxane-prostanoid (TP) receptors in the WKY, but involves the dual activation EP and TP receptors in the SHR. SQ29,548, BAYu3405 and Terutroban (TP receptor antagonists), and AH6809 (non-selective EP receptor antagonist) abolished, while SC19220 (preferential EP1 receptor antagonist) did not inhibit endothelium-dependent contractions. Both SC19220 and AH6809 significantly inhibited contractions to U46619 (TP receptor agonist). Conclusion The present study demonstrates that the contraction caused by PGE(2) in the SHR aorta is dependent on the activation of EP1 and TP receptors, but that endothelium-dependent contractions do not require the former. Thus, PGE(2). is unlikely to be an endothelium-derived contracting factor in this artery. The ability of AH6809 to inhibit endothelium-dependent contractions can be attributed to its partial antagonism at TP receptors. Nevertheless, the impairment of PGE(2)-mediated relaxation may contribute to endothelial dysfunction in the aorta of the SHR.