Effect of Epidermal Growth Factor (EGF) infusion on Small Intestinal (SI) EGF-Receptor (EGF-R) expression in a fetal rabbit model of Intrauterine Growth Retardation (IUGR)

Introduction. IUGR infants have impaired GI function with resultant feeding difficulties. Supplemented amniotic fluid swallowed by the developing fetus is a potential prenatal treatment for IUGR. Rabbits have naturally occurring IUGR fetuses based on uterine position. Previous studies administering intra-amniotic EGF (a mucosal proliferative peptide) to IUGR rabbits normalized fetal weight, SI proliferation, and villus height. Expression of the EGF-R in response to intra-amniotic EGF infusion has not yet been determined. Methods. Eight rabbits underwent placement of intra-amniotic catheters into two normal-growth (Nl) and two IUGR fetuses per mother on gestational day 24. Mini-osmotic pumps infused either EGF (300 μg/kg/day) or control solution forming four study groups (EGF-Nl versus Cont-Nl; EGF-IUGR versus Cont-IUGR). At term on gestational day 31, the fetal GI tract was harvested. SI EGF-R expression was analyzed by RT/PCR (vs. GAPDH), immunohistochemistry, and Western blot. Statistical analysis was performed using Students’ t- test Results. Native EGF-R mRNA expression at term was lower in IUGR fetuses versus normals (0.39 ± 0.05 Cont-Nl versus 0.26 ± 0.07 Cont-IUGR; P = 0.1). EGF infusion tended to decrease EGF-R mRNA expression in normal fetuses, but had no effect in IUGR fetuses. IHC localized the EGF-R to blood vessels and the villi of luminal enterocytes. EGF infusion increased EGF-R density as seen by IHC in the IUGR fetus, being particularly prominent in the submucosa and mucosal blood vessels; no difference was seen in normals. Western blot analysis confirmed EGF-R protein throughout the SI. Conclusions. EGR-R was characterized in both normal and IUGR fetal rabbits by mRNA expression, IHC localization, and protein product expression with different patterns of native expression and response to EGF infusion. Despite a reduction in EGF-R in response to EGF infusion in normals, IUGR fetuses retained robust receptor expression, supporting the particular responsiveness of the IUGR fetus to EGF infusion. The in utero treatment of IUGR with intra-amniotic EGF infusion is further supported.