Fetal Rat Utilization of ⁵⁵Fe Absorbed by Fetal Intestine From Swallowed Amniotic Fluid

Radioiron(⁵⁵Fe) injected directly into the amniotic cavity of 21-day rat fetuses is swallowed and rapidly absorbed by the intestine. The radioisotope is then transported from the intestine and is utilized in the liver and spleen, fetal erythropoietic and iron-storing organs. The level of incorporation in intestine, spleen, and liver, as measured by scintillation counting, is relatively low during the first hour, but increases 3 and 6 hr postinjection. Radioautograms at 6 hr demonstrate extensive labeling in the cytoplasm of absorptive cells in the intestinal mucosa. In liver the ⁵⁵Fe is observed in parenchymal and reticuloendothelial cells and in developing red cells. Erythroid cells are the principal ⁵⁵Fe-labeled cells in the spleen. Recirculation of some ⁵⁵Fe occurred between ⁵⁵Fe-injected fetuses, maternal organs, and control fetuses. Fetal swallowing of ⁵⁵Fe within amniotic fluid followed by intestinal absorption of the radioisotope demonstrates the existence of a pathway by which nutrients can be delivered to the fetus. This finding is of potential benefit to the human fetus since a number of compounds, including certain drugs, may possibly be administered via this route.