Interaction between Nitric Oxide and Cyclooxygenase Pathways in Endothelial Cells

Nitric oxide (NO) and cyclooxygenase (COX) derived prostaglandins (PGs) are involved in vascular homeostasis. Contradictory results have been obtained in previous studies on the putative ‘cross-talk’ between these two pathways. Our aim was to evaluate the interaction between NO and PG release in human microvascular endothelial cells (HMEC-1) and in umbilical vein endothelial cells (HUVEC). Methods: Medium samples were assayed for nitrite/nitrate (NOx) and L-citrulline levels while lysed cells were assayed for endothelial NO synthase (eNOS), as markers of NO production. Prostaglandin E₂ (PGE₂) and 6-keto-prostaglandin F1α (6-keto-PGF1α) were assessed as indicators of COX activity. Results: The NO donor sodium nitroprusside and L-arginine increased PGs levels in both cell types. NG-monomethyl-L-arginine (L-NMMA) significantly inhibited 6-keto-PGF1α release without significantly reducing PGE₂levels. Indomethacin increased both NOx, eNOS and L-citrulline levels. PGE₂ treatment did not modify NOx values. Conclusion: The stimulation of PGs by NO may represent an additional pathway used by exogenous nitrovasodilators to elicit vasodilation. Reduction of PGs by inhibition of COX was compensated by enhanced NO. Conversely, PGsdid not compensatedecreased NO following L-NMMA treatment. Treatment with the vasodilatator prostaglandin E₂did not modifyNOx levels.