Characterization of exocoelomic fluid protein from rat conceptuses cultured in rat and human sera: a measure of yolk sac activity during organogenesis.

Fluid from the extraembryonic coelom of 11.5-day rat embryos cultured in 100% rat serum, 100% human serum and 90% human serum supplemented with 10% rat serum between days 9.5 and 11.5 postconception were compared using polyacrylamide gel electrophoresis and crossed immunoelectrophoresis. The protein composition of the exocoelomic fluids differed considerably from one another and from each of their respective culture sera. The majority of proteins in the exocoelom were derived from macromolecular transport but some contribution was made from protein synthesis by the conceptus. Eighteen proteins normally found in rat serum were found in the exocoelom of conceptuses cultured in 100% rat serum. Eighteen proteins were found in the exocoelom of rat conceptuses cultured in 100% human serum, of which ten were derived from human serum and eight were proteins normally found in rat serum. Analysis of fluid from conceptuses cultured in 90% human serum supplemented with 10% rat serum showed eleven human serum proteins and ten rat serum proteins. Differences in the composition of both human and rat proteins between the latter two fluids were also evident.