L-arginine erythrocyte transport increases during pregnancy and immediately postpartum

Objective This study was undertaken to evaluate erythrocyte membrane transport of L-arginine in pregnancy and immediately postpartum. Study design The study comprised 103 women with normal pregnancy, initially evaluated at the second trimester (II), followed into the third trimester (III), and immediately postpartum (PP). Total erythrocyte L-arginine uptake was measured with 14C-L-arginine, at 37°C, for 3 minutes. The maximal transport capacity (Vmax) and half-saturation constant (Km) were obtained with the use of Michaelis-Menten kinetics. Results are expressed as mean±SD. Analysis of variance, followed by Tukey test, was used in statistical analysis (α≤.05). Results Vmax (μmol/L cells per hour) progressively increased at each consecutive time period: 779±283, 946±289, and 1349±390, at II, III, and PP, respectively (P<.001). Similarly, Km (μmol/L) values increased from 56±20 at time II, to 62±18 at time III, and 69±24 at PP (P<.001). Conclusion Total erythrocyte L-arginine uptake (Vmax and Km) increases progressively along normal pregnancy, with a further increase immediately postpartum.