Does Extracellular L-arginine Influence Nitric Oxide Production by Pulmonary Arterial Endothelial Cells?

Abstract 248 Poster Session III, Monday, 5/3 (poster 100)

Diseases such as septic shock are characterized by overproduction of nitric oxide (NO), however completely blocking NO production with non-specific NO synthase inhibitors has not improved outcome. The intracellular level of L-arginine (L-arg) is thought to approximate the plasma levels of 40 -100 µM, and these levels should be saturating for NO synthase. However, if the level of extracellular L-arg influences NO production, then NO production may be limited in the absence of extracellular L-arg, and this may represent another treatment modality in diseases such as septic shock. To test this hypothesis, pulmonary arterial endothelial cells (PAEC) were grown to confluence on Biosilon carrier beads in RPMI 1640 media which contained either 1 mM L-arg (L-arg +) or 0 mM L-arg (L-arg -). Biosilon beads without PAEC were run as a control (blank). After 24 hours, the cells were washed with Hanks-Heneslit buffer and then suspended in 2 ml of Hanks-Heneslit buffer. Samples were obtained after 120 minutes incubation for determination of nitrite (the stable product of NO metabolism) using chemiluminescence and NaI reduction. The results are shown in figure. The cells grown in L-arg- media had only 16% of the NO production of cells grown in L-arg+ media (* different from L-arg+, p<0.05). The results suggest that in the absence of extracellular L-arg NO production is limited in pulmonary arterial endothelial cells. We speculate that the reduction of circulating L-arg may be a means of limiting NO production in disorders associated with NO overproduction without completely blocking basal NO production.

Fig 1

No caption available

Funded by the American Heart Association