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.