Serum L-homoarginine concentration is elevated during normal pregnancy and is related to flow-mediated vasodilatation.

BACKGROUND Normal pregnancy is associated with enhanced vasodilatation because of the increased nitric oxide (NO) production. Because L-homoarginine can act as a substrate for NO production, concentrations of L-homoarginine in normal pregnancy were assessed in the present study to test whether L-homoarginine is associated with endothelial function. METHODS AND RESULTS Healthy non-pregnant (n=61) and pregnant women (n=58) were studied in a cross-sectional study. L-homoarginine, L-arginine, asymmetric dimethylarginine and symmetric dimethylarginine concentrations were determined simultaneously by high-performance liquid chromatography. Endothelium-dependent brachial artery flow-mediated dilation (FMD) was measured by ultrasound. The serum L-homoarginine concentration was significantly higher during the second and the third trimesters compared with the levels in the non-pregnant women (4.8+/-1.7 and 5.3+/-1.5 vs 2.7+/-1.0 micromol/L, p<0.001, respectively). In line with this, FMD increased in response to pregnancy (p<0.05). Three months after delivery, the L-homoarginine concentrations and FMD were comparable to those recorded in the non-pregnant females. The concentration of L-homoarginine correlated significantly with gestational age (r=0.426, p=0.001) and brachial artery diameter and FMD (r=0.362, p=0.006 and r=0.306, p=0.022, respectively) in pregnancy. CONCLUSIONS L-homoarginine appears to be increased during the second and third trimesters of pregnancy and may contribute to the enhanced endothelial function in normal pregnancies.