Production of slow alpha2-globulin in the pregnant rat

Slow alpha2-globulin (salpha2G), a high molecular weight glycoprotein, appears as a component of rat serum in a wide variety of both physiologic and pathologic conditions, including pregnancy; it is also present in the neonate. In the present study, the protein was detectable in serum after 6 to 10 days, and was present at moderate levels on day 13, and thereafter through the rest of pregnancy. From immunofluorescent localization and 14C-labelled amino acid incorporation studies, salpha2G was found to be localized in uterine and placental tissues and to be synthesized by these tissues as early as day 6 of gestation. Production continued throughout pregnancy. Synthesis in the liver of the pregnant rat began at day 17 of gestation, which is in contrast with the observation in pathologic conditions that liver synthesis is an initial source of the serum protein; substantial fetal liver synthesis was occurring at day 21 of gestation, and the amount in fetal serum was four times greater than that in maternal serum at that time. It is likely that the fetal liver produces salpha2G as soon as it begins to function.