Endothelin-1 inhibits the expression of inducible nitric oxide synthase.
Because nitric oxide (NO.) and endothelin (ET)-1 frequently have opposing effects on physiological and inflammatory processes, we sought to determine whether ET-1 regulates NO. synthesis by the inducible isoform of NO. synthase (iNOS). L2 cells are a rat lung epithelial cell line that synthesizes ET-1 and in which ET-1 has an autocrine role. In the current study, we demonstrate that L2 cells generate the oxidative products of NO., nitrite and nitrate, after exposure to tumor necrosis factor-alpha, lipopolysaccharide, and interferon-gamma. Exposure to these cytokines also dramatically increases the expression of iNOS mRNA. NG-monomethyl-L-arginine, dexamethasone, and cycloheximide prevent the cytokine-mediated increase in NO. oxidative products, demonstrating that iNOS accounts for their generation. Because L2 cells synthesize ET-1, to test the effect of removing endogenous ET-1, we used phosphoramidon (an ET-converting enzyme inhibitor) or BQ-123 (an ET receptor A antagonist). Removal of endogenous ET-1 with either phosphoramidon or BQ-123 significantly augments cytokine-stimulated NO. synthesis by approximately 20%. To further test the effect of ET-1 on iNOS, we treated cells with phosphoramidon to inhibit endogenous ET-1 synthesis and then administered ET-1 (10(-9) to 10(-7) M). In this setting, ET-1 significantly decreases inducible NO. production by 33% and iNOS mRNA by 50%. We conclude that ET-1 can decrease inducible NO. synthesis by cytokine-stimulated lung epithelial cells.
Markewitz
B A
BA
Department of Medicine, Overton Brooks Veterans Affairs Medical Center, Shreveport, Louisiana 71101, USA.
Michael
J R
JR
Kohan
D E
DE
D000818:Animals; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D016207:Cytokines / Q000494:pharmacology*; D017931:DNA Primers; D003907:Dexamethasone / Q000494:pharmacology; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000096:biosynthesis / Q000494:pharmacology*; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004848:Epithelium; D006020:Glycopeptides / Q000494:pharmacology; D006801:Humans; D008168:Lung; D009566:Nitrates / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D009573:Nitrites / Q000378:metabolism; D010456:Peptides, Cyclic / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D044022:Receptor, Endothelin A; D011994:Recombinant Proteins / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D019323:omega-N-Methylarginine / Q000494:pharmacology
D016207:Cytokines; D017931:DNA Primers; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D004791:Enzyme Inhibitors; D006020:Glycopeptides; D009566:Nitrates; D009573:Nitrites; D010456:Peptides, Cyclic; D012333:RNA, Messenger; D044022:Receptor, Endothelin A; D011994:Recombinant Proteins; D019323:omega-N-Methylarginine; D003907:Dexamethasone; D003513:Cycloheximide; D019001:Nitric Oxide Synthase; C072247:cyclo(Trp-Asp-Pro-Val-Leu); C008890:phosphoramidon