Objectives: Hyperuricemia provokes endothelial dysfunction (ECD). Decreased endothelial nitric oxide synthase (eNOS) activity is an important source of ECD. Cationic amino acid transporter-1 (CAT-1) is the specific arginine transporter for eNOS. We hypothesize that hyperuricemia inhibits arginine uptake. Methods: Experiments were performed in freshly harvested aortas from untreated animals and rats fed with oxonic acid (hyperuricemia), and compared to hyperuricemic rats treated with either allopurinol, benzbromarone or arginine. Results: Arginine transport was significantly decreased in hyperuricemia. Benzbromarone and arginine prevented the decrease in arginine transport in hyperuricemic rats while allopurinol did not. Arginine transport was significantly decreased in control rats treated with allopurinol. Blood pressure response to acetylcholine was significantly attenuated in hyperuricemic rats, an effect which was prevented in all other experimental groups. L-NAME inhibitable cGMP response to carbamyl-choline was significantly decreased in hyperuricemic rats and this was completely prevented by both benzbromarone and arginine, while allopurinol partially prevented the aforementioned phenomenon. Hyperuricemia induced a significant increase in protein nitration that was prevented by benzbromarone, allopurinol, and arginine. Protein abundance of CAT-1, PKCα, and phosphorylated PKCα remained unchanged in all experimental groups. Conclusions: In hyperuricemia, the decrease in aortic eNOS activity is predominantly the result of attenuated arginine uptake.

Endothelial cell dysfunction (ECD) is a common feature of chronic renal failure (CRF). Defective nitric oxide (NO) generation due to decreased endothelial NO synthase (eNOS) activity is a crucial parameter characterizing ECD. L-arginine is the sole precursor for NO biosynthesis. Among several transporters that mediate L-arginine uptake, cationic amino-acid transporter-1 (CAT-1) acts as the specific arginine transporter for eNOS. Our hypothesis implies that CAT-1 is a major determinant of eNOS activity in CRF. We studied glomerular and aortic arginine uptake, CAT-1, and CAT-2 messenger ribonucleic acid (mRNA) expression, and CAT-1 protein in: (a) rats 6 weeks following 5/6 nephrectomy (CRF), (b) sham-operated animals, and (c) rats with CRF treated orally with either atorvastatin or arginine in drinking water (modalities which have been shown to enhance eNOS activity and improve endothelial function). Both glomerular and aortic arginine transport were significantly decreased in CRF. Treatment with either arginine or atorvastatin abolished the decrease in arginine uptake in CRF rats. Using reverse transcriptase-polymerase chain reaction and Northern blotting, we found a significant increase in glomerular and aortic CAT-1 mRNA expression in CRF. Western blotting revealed that CAT-1 protein was decreased in CRF, but remained intact following arginine and atorvastatin administration. Renal and systemic arginine uptake is attenuated in CRF, through modulation of CAT-1 protein. These findings provide a possible novel mechanism to eNOS inactivation and endothelial dysfunction in uremia.

While a specific role for nitric oxide (NO) in inducing the hemodynamic alterations of pregnancy is somewhat controversial, it is widely accepted that excess NO is generated during pregnancy. L-Arginine is the sole precursor for NO biosynthesis. Among several transporters that mediate L-arginine uptake, cationic amino acid transporter-1 (CAT-1) acts as the specific arginine transporter for endothelial NO synthase. The present study was designed to test the hypothesis that, during pregnancy, when arginine consumption by the fetus is significantly increased, compensatory changes in maternal arginine uptake affect the endothelium. Uptake of radiolabeled arginine (L-[3H]arginine) by freshly harvested maternal aortic rings from pregnant rats decreased by 65 and 30% in mid- and late pregnancy, respectively, compared with those obtained from virgin animals. This decrease was associated with a significant increase in endothelial protein nitration (the footprint of peroxynitrite generation), as shown by both Western blotting and immunohistochemistry utilizing anti-nitrotyrosine antibodies, reflecting endothelial damage. Northern blot analysis revealed that steady-state aortic CAT-1 mRNA levels did not change throughout pregnancy, whereas CAT-1 protein abundance was significantly increased, peaking at mid-pregnancy. Protein content of protein kinase C (PKC)-alpha, which was previously shown to decrease CAT-1 activity, increased significantly in the pregnant animals and was associated with a significant increase in CAT-1 phosphorylation. Intraperitoneal injection of alpha-tocopherol, a PKC-alpha inhibitor, prevented the decrease in arginine transport and attenuated protein nitration. In conclusion, aortic arginine uptake is reduced during pregnancy, through posttranslational modulation of CAT-1 protein, presumably via upregulation of PKC-alpha. The aforementioned findings are associated with an increase in protein nitration and, therefore, in selected individuals, may lead to the development of certain forms of endothelial dysfunction, like preeclampsia.