l-Glutamine Inhibits Nitric Oxide Synthesis in Bovine Venular Endothelial Cells1
- Departments of 1Medical Physiology (C.J.M., G.W.) and 2Animal Science (G.W.) Texas A&M University, College Station, Texas
Abstract
This study was conducted to test the hypothesis thatl-glutamine has differential effects on nitric oxide (NO) synthesis from l-arginine in bovine venular endothelial cells (EC) stimulated by A23187 (a Ca++ionophore) and receptor-mediated vasodilators (bradykinin and substance P). EC were cultured at 37°C for 24 h in the presence of 0.4 mMl-arginine and 0.0 to 2.0 mM l-glutamine with or without 1 μM A23187, 1 μM bradykinin or 10 μM substance P. The release of nitrite and nitrate by EC was used as an indicator of NO synthesis. A23187, bradykinin or substance P increased NO synthesis from l-arginine by EC in the presence or absence of l-glutamine. The addition ofl-glutamine (0.5 and 2 mM) markedly increased intracellular concentrations of l-glutamine, l-glutamate andl-aspartate and decreased NO synthesis by EC in a concentration-dependent manner in the presence or absence of A23187, bradykinin or substance P. l-Glutamine had no effect on l-arginine uptake by EC or on intracellular l-arginine concentration. Neitherl-glutamine nor its glutaminase metabolites (ammonia,l-glutamate and l-aspartate) had any effect on endothelial NO synthase activity. Taken together, these results suggest that the inhibition by l-glutamine of NO synthesis froml-arginine is unlikely to result from an effect ofl-glutamine on l-arginine transport or NO synthase activity. Although the mechanism involved remains unknown, regulation of the arginine-NO pathway by l-glutamine may have pharmacologic and therapeutic implications in such conditions as inflammation and septic shock by inhibiting NO generation froml-arginine in endothelial cells.
Footnotes
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Send reprint requests to: Cynthia J. Meininger, Department of Medical Physiology, Texas A&M University, College Station, TX 77843-1114.
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↵1 This research was supported by Grants-in-Aid from the American Heart Association (No. 95013030 and 95009150) and by an interdisciplinary grant from Texas A&M University.
- Abbreviations:
- BH4
- (6R)-5,6,7,8-tetrahydro-l-biopterin
- BSA
- bovine serum albumin
- DMEM
- Dulbecco’s modified Eagle’s medium
- DPBS
- Dulbecco’s phosphate-buffered saline
- EC
- endothelial cells
- ECGF
- endothelial cell growth factor
- FBS
- fetal bovine serum
- KHB
- Krebs-Henseleit bicarbonate
- NO
- nitric oxide
- PBS
- phosphate-buffered saline
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- Received July 10, 1996.
- Accepted December 24, 1996.
- The American Society for Pharmacology and Experimental Therapeutics
