Cytokine treatment increases arginine metabolism and uptake in bovine pulmonary arterial endothelial cells.

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Abstract
L-Arginine (l-Arg) is metabolized to nitric oxide (NO) by NO synthase (NOS) or to urea by arginase (AR). l-Arg is transported into bovine pulmonary arterial endothelial cells (BPAECs) by cationic amino acid transporter-2 (CAT-2). We hypothesized that cytokine treatment would increase l-Arg metabolism and increase CAT-2 mRNA expression. BPAECs were incubated for 24 h in medium (control) or medium with lipopolysaccharide and tumor necrosis factor-α (L-T). L-T increased nitrite production (3.1 ± 0.4 nmol/24 h vs. 1.8 ± 0.1 nmol/24 h for control; P< 0.01) and urea production (83.5 ± 29.5 nmol/24 h vs. 17.8 ± 8.6 nmol/24 h for control; P < 0.05). L-T-treated BPAECs had greater endothelial and inducible NOS mRNA expression compared with control cells. Increasing the medium l-Arg concentration resulted in increased nitrite and urea production in both the control and the L-T-treated BPAECs. L-T treatment resulted in measurable CAT-2 mRNA. L-T increasedl-[3H]Arg uptake (5.78 ± 0.41 pmol vs. 4.45 ± 0.10 pmol for control; P < 0.05). In summary, L-T treatment increased l-Arg metabolism to both NO and urea in BPAECs and resulted in increased levels of CAT-2 mRNA. This suggests that induction of NOS and/or AR is linked to induction of CAT-2 in BPAECs and may represent a mechanism for maintainingl-Arg availability to NOS and/or AR.

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