L-Citrulline Supplementation Enhances Fetal Growth and Protein Synthesis in Rats with Intrauterine Growth Restriction

Abstract

Background: Intrauterine growth restriction (IUGR) results from either maternal undernutrition or impaired placental blood flow, exposing offspring to increased perinatal mortality and a higher risk of metabolic syndrome and cardiovascular disease during adulthood. L-Citrulline is a precursor of L-arginine and nitric oxide (NO), which regulates placental blood flow. Moreover, L-citrulline stimulates protein synthesis in other models of undernutrition.Objective: The aim of the study was to determine whether L-citrulline supplementation would enhance fetal growth in a model of IUGR induced by maternal dietary protein restriction.Methods: Pregnant rats were fed either a control (20% protein) or a low-protein (LP; 4% protein) diet. LP dams were randomly allocated to drink tap water either as such or supplemented with L-citrulline (2 g · kg−1 · d−1), an isonitrogenous amount of L-arginine, or nonessential L-amino acids (NEAAs). On day 21 of gestation, dams received a 2-h infusion of L-[1-13C]-valine until fetuses were extracted by cesarean delivery. Isotope enrichments were measured in free amino acids and fetal muscle, liver, and placenta protein by GC–mass spectrometry.Results: Fetal weight was ∼29% lower in the LP group (3.82 ± 0.06 g) than in the control group (5.41 ± 0.10 g) (P < 0.001). Regardless of supplementation, fetal weight remained below that of control fetuses. Yet, compared with the LP group, L-citrulline and L-arginine equally increased fetal weight to 4.15 ± 0.08 g (P < 0.05) and 4.13 ± 0.1 g (P < 0.05 compared with LP), respectively, whereas NEAA did not (4.05 ± 0.05 g; P = 0.07). Fetal muscle protein fractional synthesis rate was 35% lower in the LP fetuses (41% ± 11%/d) than in the control (61% ± 13%/d) fetuses (P < 0.001) and was normalized by L-citrulline (56% ± 4%/d; P < 0.05 compared with LP, NS compared with control) and not by other supplements. Urinary nitrite and nitrate excretion was lower in the LP group (6.4 ± 0.8 μmol/d) than in the control group (17.9 ± 1.1 μmol/d; P < 0.001) and increased in response to L-citrulline or L-arginine (12.1 ± 2.2 and 10.6 ± 0.9 μmol/d; P < 0.05), whereas they did not in the LP + NEAA group.Conclusion: L-Citrulline increases fetal growth in a model of IUGR, and the effect may be mediated by enhanced fetal muscle protein synthesis and/or increased NO production.