Ceruloplasmin, serotransferrin and albumin presented different abundance in mares' uterine fluid five days after insemination.

Characterization of the uterine proteome before the entry of the conceptus to the uterus is essential to know the factors involved in the physiological events of gestation. The objective of the study was to compare proteomic profile of uterine fluid collected on day 5 post ovulation of cyclic and inseminated mares. Samples of endometrial secretion were recovered over 2 cycles during the fifth day post ovulation. The first cycle constituted the Cyclic group and in the following cycle, the same mares were inseminated and considered as the Inseminated group. All the samples were subjected to two-dimensional electrophoresis (2D-PAGE). A total of 107 spots were visualized by 2D-PAGE. Three spots with differences in abundance between the inseminated and cyclic mares and with presence in at least 80% in one of the groups were selected and identified. The selected spots were extracted, digested by trypsin and analyzed by matrix assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometry (MS) for protein identification. Three proteins were identified: ceruloplasmin (CP) serotransferrin (TF) and albumin (ALB). The identified proteins in this study were related to iron metabolism and immunological tolerance suggesting that changes in their abundance during the 5 days after ovulation are probably a signaling mechanism of the potential equine conceptus to the maternal immune system for its immunological recognition. Probably changes in abundance of CP, ALB and TF represent a mechanism of endometrial preparation for the maternal recognition, attachment and development of a potential equine embryo. There is also evidence to support an alternative hypothesis suggesting that protein changes are inflammatory events, resulting from a previous inflammation due to residual seminal effects.