Uptake and distribution of exogenous serum proteins in the cultured rat embryo

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Abstract
Head fold stage rat embryos were cultured on a medium consisting of adult rat serum for 48 hr. During the final 10 or 20 hr of culture [35S]‐methionine was added to the medium. Sera from visceral yolk sac blood vessels, exocoelomic cavity fluid, and amniotic sac fluid were analyzed by SDS‐polyacrylamide gel electrophoresis followed by Amido Black staining and fluorography. Amido Black staining showed bands in all three embryonic fluid compartments which migrated at rates comparable to transferrin, alpha‐feto‐protein, albumin, IgG, and hemoglobin. Fluorography, however, showed that radioactivity was restricted to alpha‐fetoprotein, IgG, and hemoglobin. This suggested that at least some transferrin and albumin were transferred intact from the exogenous medium to the embryonic fluid compartments.