PROSTAGLANDIN-MEDIATED INHIBITION OF NITRIC-OXIDE PRODUCTION BY BOVINE AORTIC ENDOTHELIUM DURING HYPOXIA

Objective: The present study utilized a monoculture of vascular endoth elium to: (1) determine if nitric oxide (NO) production was decreased during hypoxia, (2) ascertain if specific prostaglandins were released in response to hypoxia, and (3) determine if cyclo-oxygenase inhibiti on would modulate hypoxia-induced decreases in NO production. Methods: Bovine aortic endothelial cells (BAE cells) were grown to confluence on microcarrier beads. NO released in response to the receptor-indepen dent agonist, A23187 calcium ionophore, was directly and continuously measured using a sensitive and specific chemiluminescence method. Cell s were exposed to either ''hypoxia'' (pO(2) = 10 mmHg) or ''normoxia'' (pO(2) = 160 mmHg) for 30 min. NO was quantitatively measured with an d without indomethacin (1.7 mu M) in the incubation medium, and also f ollowing incubation with the prostacyclin analog, iloprost. The prosta glandins PGI(2) and PGE(2) released in response to hypoxia were quanti tated using an enzyme immunoassay. Results: Hypoxia significantly decr eased NO production, resulting in a 22.8(2.1)% reduction in NO from 94 .3(5.3) nmol/mu g protein (during normoxia) to 73.5(2) nmol/mu g prote in (during hypoxia). Hypoxia significantly stimulated the production o f PGI(2) and PGE(2), in excess of that released in response to A23187 when compared with normoxia. Following cyclo-oxygenase inhibition, the hypoxia-induced decrease in NO production was abolished (0.13 [2.7] % change relative to controls). Furthermore, iloprost (10 nM) directly inhibited NO production. Conclusions: The results demonstrate that ion ophore-stimulated NO production is sensitive to oxygen tension, decrea sing in response to hypoxia. Inhibition of prostaglandin synthesis res tores NO production during hypoxia, while iloprost directly suppresses NO production. Thus, endothelium-derived prostanoids produced in resp onse to hypoxia may modulate NO production via an autocrine negative f eedback mechanism.