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 nitric oxide synthase (eNOS). The current 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 radio-labeled arginine {[³H] L-arginine} by freshly harvested maternal aortic rings from pregnant rats decreased by 65 and 30 % in mid and late pregnancy respectively, compared to 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) , 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 -tocopherol, a PKC inhibitor prevented the decrease in arginine transport and attenuated protein nitration. In conclusion: aortic arginine uptake is reduced during pregnancy, through post translational modulation of CAT-1 protein, presumably via upregulation of PKC. 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.