EPIDERMAL GROWTH FACTOR RECEPTOR IS NOT ALTERED IN CONTENT OR FUNCTION IN RESPONSE TO OLIGOHYDRAMNIOS IN THE FETAL LUNG. 295

Epidermal growth factor (EGF) receptor is a member of the tyrosine kinase family and initiates mitogenesis via phosphorylation. The EGF family is believed to have a major role in embryogenesis and organogenesis, and in particular, play a vital role in fetal lung development. It is not known whether the pulmonary hypoplasia which occurs in response to oligohydramnios(O) is mediated via a decrease in EGF receptor number or function in this model of decreased lung growth. In 8 pregnant rat mothers, on d 16 of the pregnancy, we induced O in half of each litter by puncturing the amniotic sac and allowing amniotic fluid drainage until delivery. The fetal lungs were harvested on d 21 and EGFR mRNA was determined by RTPCR in control and hypoplastic (O) lungs. The PCR bands were normalized to β actin and the bands converted to densitometric units. Immunoblotting also was performed on lung cell membranes using antiEGFR and antiphosphotyrosine antibodies. The function of the EGFR was determined by phosphorylation of the lung cell membranes before and after stimulation with EGF. After incubation with³² P, the cell lysates were immunoprecipitated with both antiEGFR and antiphosphotyrosine antibodies. We found that although O caused a significant decrease in lung size (C: 182 ± 7 v O: 145 ± 9 mg,p≤0.002), the mRNA for EGFR was not decreased per lung (C: 0.86± 0.27 v O: 0.80 ± 0.24 units, p =NS) or per mg of lung (C: 4.6 ± 1.4 v O: 5.4 ± 1.6 units/mg lung X1000,p =NS), nor were differences seen in receptor amount as determined by immunoblotting. In addition, the C and O membranes showed similar levels of baseline EGFR phosphorylation before stimulation by EGF, and immunoprecipitated equally for both antiEGFR and antiphosphotyrosine antibodies. Importantly, phosphorylation of both C and O EGFR each increased 4 fold in response to EGF stimulation. We conclude that pulmonary hypoplasia in response to O is unlikely to result from decreased EGFR number or function, and that EGFR in hypoplastic lungs remain responsive to EGF in this model. This suggests a potential therapeutic modality for decreased fetal lung growth.