Fig. 2
Proposed mechanisms responsible for beneficial effects of dietary L-arginine supplementation in improving embryonic/fetal growth and survival in gestating swine. L-Arginine stimulates the synthesis of tetrahydrobiopterin [BH4, a required co-factor for nitric oxide (NO) synthase)] from GTP via the GTP cyclohydrolase-I (GCH1) pathway, thereby augmenting NO production by placental tissue. L-Arginine also increases the activity of ornithine decarboxylase (a key enzyme for the synthesis of polyamines). Both NO and polyamines, as well as growth factors (such as placental growth factor, vascular endothelial growth factor A120, and vascular endothelial growth factor receptors 1 and 2) promote placental angiogenesis and growth (including vascular growth) to increase rates of transfer of non-water nutrients [including amino acids (AAs)] and oxygen across the placenta from mother to embryo/fetus. In addition, L-arginine elevates the concentrations of both cGMP and cAMP in the placenta to increase the expression of aquaporins (AQPs) to promote the placental transport of water from mother to embryo/fetus. Ultimately, the coordinate actions of L-arginine result in improvements in the growth and survival of embryos/fetuses