Changes in the protein content of mouse uterine flushings during normal pregnancy and delayed implantation, and after ovariectomy and oestradiol administration

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Abstract
Summary. The protein content of the mouse uterine lumen increased significantly (P < 0·001) on Day 4 of pregnancy, the day of implantation. This increase was associated with the presence of 14 serum and 22 non-serum proteins in the lumen; the major serum proteins were classed as high molecular weight slow α-globulins, while the dominant non-serum components consisted of slow and fast α-globulins, 6 prealbumins and a large quantity of proteinaceous material migrating near the origin of the gels. During experimental and lactational delayed implantation the protein levels were constantly low, transferrin, haemoglobin and albumin dominating the protein pattern. After administration of oestradiol-17β, however, a biphasic uterine response was detected, significant increases in luminal protein concentration being observed within 12 h and again at 40–48 h after injection. The first phase of this response involved an influx of serum and non-serum proteins into the uterine lumen, most proteins migrating as high molecular weight slow α-globulins. The second phase involved an increase in the intensity of many non-serum components, the major proteins having Ra values of 0·06,0·10 and 0·32. The qualitative, but not the quantitative, aspects of this response to oestradiol were identical in the absence of blastocysts.