Effect of epidermal growth factor on placental amino acid transport and regulation of epidermal growth factor receptor expression of hepatocyte in rat

We investigated the effect of epidermal growth factor (EGF) on amino acid transport in the rat placenta and the hormonal and nutritional regulation of hepatic expression of epidermal growth factor receptor (EGFR). Fetuses horn to maternal rats administered EGF were larger than control fetuses, while fetuses born to mothers administered EGF antibody were smaller than controls. The fetomaternal amino acid concentration ratio (fetal blood/maternal blood) was higher in the EGF-treated group than in the control group, and was lower in the EGF antibody-treated group. EGF treatment stimulated C-14-aminoisobutyric acid, isoleucine and alanine uptake by placental explants as did treatment with insulin-like growth factor-I and insulin, which have been reported to stimulate the active amino acid transport. Thus, EGF promoted amino acid transport in the rat placenta and influenced fetal growth as a result. In addition, retinol induced a 170% increase of EGF binding to rat hepatocytes and insulin induced a 120% increase of EGF binding, while amino acids (isoleucine and serine) had no effect on EGF binding. This result indicated that there is hormonal regulation of EGF binding to hepatocytes and that changes of some hormone levels may affect hepatic ECGR expression.