Analysis of human uterine luminal fluid proteins following radiolabeling by reductive methylation: comparison of proliferative and secretory phase samples.

The proteins contained in human uterine luminal washings of proliferative and secretory phase endometria were depleted of albumin by affinity chromatography and labeled with either 3H or 14C by reductive methylation. Samples of human serum from proliferative and secretory phases of the normal menstrual cycle were similarly treated and served as control material. Isotope mixing experiments were performed in which 3H-labeled fluid proteins were combined with 14C-labeled sera or fluid proteins and the mixture analyzed by two-dimensional gel electrophoresis. The labeled proteins were then detected by fluorography and autoradiography of the same gel. Control experiments mixing 3H- and 14C-labeled sera revealed no difference between proliferative and secretory phase samples and no isotope effect of in vitro labeling. Radiolabeled uterine luminal wash proteins, however, did show significant differences when compared to serum. Furthermore, significant differences between proliferative and secretory phase uterine fluid proteins were observed. A cluster of proteins in the pI range of 5.9 to 6.4 pH and in the molecular weight range of 60,000 -- 67,000 daltons appeared to originate from the endometrium. Among these uterine proteins, several seemed to be found only in the secretory phase of the normal menstrual cycle. The data provided evidence to support the hypothesis that the human endometrium secretes proteins that are dependent on the hormones of the menstrual cycle.