Qualitative and quantitative examination of the proteins of rat uterine luminal fluid during pro-oestrus and pregnancy and comparison with those of serum.

Rat serum and uterine luminal proteins at two distinct endocrinological stages were analyzed electrophoretically. The quantitative relationships between the major macromolecular fractions were calculated from the densitometer scans. At pro-oestrus there was a marked increase in the total luminal proteins which was probably not due to transudation of serum into the lumen because of the presence of large amounts of two proteins, of approximate mol. wt 125,000 and 130,000, which were not detected in serum. Quantitative estimates of proteins of different molecular weight fractions in the fluids showed that there were considerable differences between the three fluids, indicating that the hormones do not merely induce a free passage of serum proteins into the lumen. On Day 5 of pregnancy there was a considerable lower amount of protein in the uterine lumen and qualitatively these proteins differed from those in serum and the uterine lumen at pro-oestrus.