The Origin of Plasma Proteins in the Guinea Pig Fetus12

Abstract

The problem was approached with radioactive tracers. The injection of S35 methionine into newborn guinea pigs delivered by hysterotomy shortly before term resulted in the incorporation of radioactivity into all the electrophoretic fractions of plasma proteins except gamma globulin. The injection of S35 methionine into the pregnant guinea pig resulted in incorporation of radioactivity into all the fetal plasma proteins but the specific activity of the gamma globulin was low. These observations indicate that the fetus near term can synthesize efficiently plasma proteins, except for gamma globulin, from amino acids derived from the mother. The fetal gamma globulin is synthesized by the mother and transferred to the fetus. The transfer of intact plasma proteins from mother to fetus investigated with biosynthetically prepared (S35) plasma proteins and with I131 plasma proteins. The technical problems involved in interpreting these experiments are discussed. The results with both tracers indicate the transfer of plasma proteins from mother to fetus.