This proposal tests the hypothesis that fetal gastric epithelial development is critically dependent on the luminal action of trophic substances present in amniotic fluid. Preliminary studies show that when swallowing of amniotic fluid during the third trimester is prevented in vivo by esophageal ligation in the fetal rabbit, marked inhibition of morphologic and functional gastric development occurs. In vitro amniotic fluid has a trophic effect on cultured fetal gastric epithelial cells. The specific aims of this project are to: 1) examine the effects of known trophic agents found in amniotic fluid on the development of fetal gastric epithelium in vivo; 2) examine the effect of known trophic agents found in amniotic fluid on the growth of fetal gastric epithelial cells in vitro; and 3) isolate in a preliminary way trophic factors in amniotic fluid using the in vitro and in vivo models as bioassays. Development of gastric epithelial cells will be assessed morphometrically by light and electron microscopy, and immunoreactive staining for G-cells. Functional development will be assessed in vivo by measurements of gastric acid and pepsin secretion, and serum gastrin levels. Potentially important trophic factors to be studied include those known to affect neonatal and adult gastrointestinal growth, including: luminal nutrients, gastrin, epidermal growth factor, enteroglucagon, and cortisol. Affinity chromatography will be used to selectively remove trophic agents from amniotic fluid in order to assess their relative importance. In addition, amniotic fluid will be fractionated by high performance liquid chromatography and the trophic activity of each fraction will be tested in the in vitro and in vivo bioassays. Fractions with high activity will be characterized in a preliminary way. This work has direct health-related significance in the understanding, prevention, and treatment of developmental anomalies of the gastrointestinal tract.