Further, in-vivo studies in sheep show that maternal and fetal circulating IGF-1 concentrations interact to regulate partitioning of substrates between the fetus and placenta, with maternal IGF-1 stimulating placental glucose and amino acid uptake, whereas fetal IGF-1 stimulates fetal glucose and amino acid uptake from the placenta and inhibits fetal protein oxidation.
These interactions provide a mechanism by which fetal growth is regulated according to substrate supply