Decidual cell function: evidence for a role in the regulation of serum CBG and a 60 kDa protein during early pregnancy in the hamster.

Several serum proteins increase in titer during pregnancy. We tested the hypothesis that decidual cells may signal the production of certain serum proteins in the hamster. Measurement of serum CBG by equilibrium binding using either [3H]-progesterone or [3H]-cortisol in conjection with ion exchange chromatography showed that decidualization increased CBG levels. Two-dimensional gel electrophoresis revealed that a 60 kDa++ protein increases markedly in the serum of the hormonally pseudopregnant (PSP) animal soon after artificial induction of decidualization on PSP day 4. The 60 kDa serum protein remains low in the nondecidualized PSP animal, but it increases in the pregnant animal. A photoaffinity labeling procedure was used to covalently bind [3H]-androstadienolone to CBG. Fluorography of 2D gels run under denaturing conditions established that the 60 kDa protein did not bind steroid as did CBG (69 kDa). To determine whether decidual cells could induce the 60 kDa and CBG proteins, different numbers of decidual cells were injected IP into PSP recipients. A single injection of 50 x 10(6) decidual cells induced both serum proteins within 48h, whereas the same number of hamster fetal cells was ineffective. Thus, these results demonstrate that hamster decidual cells induce a 60 kDa protein of unknown function and serum CBG. Since the decidual cell itself does not appear to be the source of either protein, it follows that the decidual cell signals the synthesis and secretion of these proteins elsewhere in the body, most likely in the liver. To our knowledge, this is the first demonstration that the decidual cell regulates serum CBG and other proteins in this manner.