Activation of TP receptors induces high release of PGI2 in coronary arteries of renal hypertensive rats.

AIM: To investigate the molecular mechanisms and cellular signaling pathways involved in the activation of TP receptors and the consequent induction of contractile responses in coronary arteries of renal hypertensive (2K-1C) rats. METHODS AND RESULTS: The coronary perfusion pressure (CPP) was lower in 2K-1C rats during increased coronary flow as measured by the Langendorff technique. The coronary contraction and relaxation were evaluated by vascular reactivity studies, and the molecular mechanisms were investigated on the basis of the protein expression of TP receptors, Cav-1, eNOS, COX-1, and COX-2, as measured by Western blot. The levels of eicosanoids were determined by ELISA immunoassay and analyzed by reverse-phase HPLC coupled to electrospray ionization mass spectrometry (HPLC-MS/MS). The metabolites from NO production were evaluated by the Griess reaction. The coronary arteries of 2K-1C rats expressed COX-2 to a larger extent and TP receptors to a lesser extent than the coronary arteries of normotensive (2K) rats. Selective COX-1 and non-selective COX inhibitors reversed the reduction in the contraction induced by TP receptors in the coronary arteries of 2K-1C rats. U46619, an agonist of TP receptors, induced a contractile response that was relaxed by acetylcholine (ACh). In the coronary arteries of 2K-1C rats, this ACh-induced relaxation depended on COX. The activation of TP receptors increased the production of PGI2 in the coronary arteries of 2K-1C rats. The results demonstrated that increased COX signaling in the coronary arteries of 2K-1C rats mediated the low levels of CPP, the contraction induced by the activation of TP receptors, and the endothelium-dependent relaxation. The vasodilator PGI2 seemed to be the major product. CONCLUSION: Activation of TP receptors increases production of PGI2 in coronary arteries of 2K-1C rats.

Endothelial nitric oxide synthase and cyclooxygenase are activated by hydrogen peroxide in renal hypertensive rat aorta.

In this work, we hypothesized that cyclooxygenase (COX) activity can be regulated by nitric oxide (NO) and hydrogen peroxide (H2O2). In the renal hypertension (2K-1C), phenylephrine (PE)-induced contraction was lower than in normotensive (2K) rat aortas. This impaired contraction is due to NO/H2O2- induced vasodilation. We evaluated the effects of H2O2 on the activity of COX and endothelial NO-Synthase (eNOS) in 2K-1C rat aortas stimulated with PE. Responses for PE or H2O2 were evaluated in 2K-1C and 2K rat aortas, without or with inhibitors for COX (Indomethacin) or eNOS (L-NAME). COX isoforms expression was evaluated by Western blotting. eNOS inhibition was tested on thromboxane A2 (TXA2) and prostacyclin (PGI2) production. PE-induced contraction was lower in 2K-1C than in 2K. Indomethacin reduced PE-induced contraction in 2K, but it had no effect in 2K-1C. L-NAME reversed indomethacin-induced effect in 2K and it normalized PE-induced contraction in 2K-1C to the normotensive levels. COX-1 and COX-2 expression, TXA2 and PGI2 production were higher in 2K-1C than in 2K. eNOS inhibition did no modify TXA2/PGI2 production. In low concentrations, H2O2 induced relaxation only in 2K that was abolished by L-NAME while the contractions induced by high concentrations were abolished by indomethacin in both 2K and 2K-1C. The activity/expression of COX, and TXA2/PGI2 production were increased in 2K-1C, which were not modified by eNOS. High levels of H2O2 increased the endothelial COX activity, which induced contraction. Therefore, an high increase in H2O2 production may increase COX-induced vasoconstriction rather than eNOS-induced relaxation, which might contribute to aggravate hypertension.