Decreased generation of nitric oxide (NO) by endothelial NO synthase (eNOS) characterizes endothelial dysfunction (ECD). Delivery of arginine to eNOS by cationic amino acid transporter-1 (CAT-1) was shown to modulate eNOS activity. We found in female rats, but not in males, that CAT-1 activity is preserved with age and in chronic renal failure, two experimental models of ECD. In contrast, during pregnancy CAT-1 is inhibited. We hypothesize that female sex hormones regulate arginine transport. Arginine uptake in human umbilical vein endothelial cells (HUVEC) was determined following incubation with either 17β-estradiol (E2) or progesterone. Exposure to E2 (50 and 100 nM) for 30 min resulted in a significant increase in arginine transport and reduction in phosphorylated CAT-1 (the inactive form) protein content. This was coupled with a decrease in phosphorylated MAPK/extracellular signal-regulated kinase (ERK) 1/2. Progesterone (1 and 100 pM for 30 min) attenuated arginine uptake and increased phosphorylated CAT-1, phosphorylated protein kinase Cα (PKCα), and phosphorylated ERK1/2 protein content. GO-6976 (PKCα inhibitor) prevented the progesterone-induced decrease in arginine transport. Coincubation with both progesterone and estrogen for 30 min resulted in attenuated arginine transport. While estradiol increases arginine transport and CAT-1 activity through modulation of constitutive signaling transduction pathways involving ERK, progesterone inhibits arginine transport and CAT-1 via both PKCα and ERK1/2 phosphorylation, an effect that predominates over estradiol.
Keywords: endothelial function; estrogen; progesterone.
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