Serum proteins and thyroxineprotein interaction in early human fetuses.

The concentration and electrophoretic pattern of serum proteins of the fetus differ from those of the adult in animals (1-3) as well as in man (4-7). In early fetuses of some species, serum proteins have been described which are either absent or modified at later stages of development (8, 9). Pedersen (10) first recognized in the newborn calf a large amount of an unusual a-globulin for which he proposed the term fetuin. This material, which is absent in adults but present in fetuses of other species (11, 12), is an acidic glycoprotein containing glucosamine, mannose (13), galactose, galactosamine, and sialic acid (14). Relatively few such studies have been made on humans, and most of the investigations have been concerned with newborn infants. It has been observed that total serum protein is very low in the first stage of fetal life and rises continuously during development (15). A fetal serum protein migrating between albumin and a,-globulin has been recently demonstrated very early in development and found to disappear by the fourth month of gestation (16). At the present time the nature and physiological significance of this human fetal protein is not understood. The fetal thyroxine-binding proteins have been studied only in the rabbit and newborn humans. In fetal rabbits Osorio and Myant (17) found that the specific thyroxine-binding protein of the adult is not present until the later stages of development, but the fetal serum contains a different binding protein with an electrophoretic mobility intermediate between a2and 8-globulins. No qualitative difference between human newborns and adults was found (18, 19). In the present study, serum proteins and thyroxine-protein interaction were examined in human fetuses after 8 to 20 weeks of gestation.