Intrauterine growth retardation (IUGR) is associated with vascular complications leading to hypoxia and abnormal fetal development. The effect of IUGR on l-arginine transport and nitric oxide (NO) synthesis was investigated in cultures of human umbilical vein endothelial cells (HUVECs). IUGR was associated with membrane depolarization and reduced l-arginine transport (Vmax= 5.8±0.2 versus 3.3±0.1 pmol/&mgr;g protein per minute), with no significant changes in transport affinity (Km=159±15 versus 137±14 &mgr;mol/L). l-Arginine transport wastrans-stimulated (8- to 9-fold) in cells from normal and IUGR pregnancies. IUGR was associated with reduced production of l-[3H]citrulline from l-[3H] arginine, lower nitrite and intracellular l-arginine, l-citrulline, and cGMP. IUGR decreased hCAT-1 and hCAT-2B mRNA, and increased eNOS mRNA and protein levels. IUGR-associated inhibition of l-arginine transport and NO synthesis, and membrane depolarization were reversed by the NO donorS-nitroso-N-acetyl-l,d-penicillamine. In summary, endothelium from fetuses with IUGR exhibit altered l-arginine transport and NO synthesis (l-arginine/NO pathway), reduced expression and activity of hCAT-1 and hCAT-2B and reduced eNOS activity. Alterations in l-arginine/NO pathway could be critical for the physiological processes involved in the etiology of IUGR in human pregnancies.