Implantation associated changes in uterine secreted proteins

Cross sectional segments were removed from the uteri of pregnant and pseudopregnant mice and incubated in vitro with labeled amino acids. Proteins that were synthesized and secreted by these explants were separated by two-dimensional polyacrylamide gel electrophoresis and localized by fluorography. As expected, the overall amount of labeled protein secreted into the medium was greater with tissue removed from implantation sites, or an artificially induced deciduoma, than it was with tissue from non-decidualized areas. It was not possible, by means of visual examination of the gels, to determine whether qualitative changes occurred in the patterns proteins that were released. However, by means of dual label ratios, it was demonstrated that the synthesis and secretion of individual proteins was regulated differentially. Furthermore, it was found that when the stimulus for decidualization was a normal implanting embryo, the pattern of protein enhancement was different than it was with an intrauterine thread. The finding that the uterus can distinguish between these two deciduogenic stimuli implies that unique signal factors, which may be important for the establishment of pregnancy, are released by the mouse embryo before implantation.