Arginase inhibition increases nitric oxide production in bovine pulmonary arterial endothelial cells

Nitric oxide (NO) is produced by NO synthase (NOS) from L-arginine (L-Arg). Alternatively, L-Arg can be metabolized by arginase to produce L-ornithine and urea. Arginase (AR) exists in two isoforms, ARI and ARII. We hypothesized that inhibiting AR with L-valine (L-Val) would increase NO production in bovine pulmonary arterial endothelial cells (bPAEC). bPAEC were grown to confluence in either regular medium (EGM; control) or EGM with lipopolysaccharide and tumor necrosis factor-alpha (L/T) added. Treatment of bPAEC with L/T resulted in greater ARI protein expression and ARII mRNA expression than in control bPAEC. Addition of L-Val to the medium led to a concentration-dependent decrease in urea production and a concentration-dependent increase in NO production in both control and L/T-treated bPAEC. In a second set of experiments, control and L/T bPAEC were grown in EGM, EGM with 30 mM L-Val, EGM with 10 mM L-Arg, or EGM with both 10 mM L-Arg and 30 mM L-Val. In both control and L/T bPAEC, treatment with L-Val decreased urea production and increased NO production. Treatment with L-Arg increased both urea and NO production. The addition of the combination L-Arg and L-Val decreased urea production compared with the addition of L-Arg alone and increased NO production compared with L-Val alone. These data suggest that competition for intracellular L-Arg by AR may be involved in the regulation of NOS activity in control bPAEC and in response to L/T treatment.