LARGE-FORMAT, 2-DIMENSIONAL POLYACRYLAMIDE-GEL ELECTROPHORESIS OF OVINE PERIIMPLANTATION UTERINE LUMINAL FLUID PROTEINS - IDENTIFICATION OFALDOSE REDUCTASE, CYTOPLASMIC ACTIN, AND TRANSFERRIN AS CONCEPTUS-SYNTHESIZED PROTEINS

Early pregnancy in ruminants, such as the sheep, is characterized by r elatively extensive development of the conceptus before attachment to the endometrium. Between the period of blastocyst hatching and initial attachment, the uterus responds to signals from the conceptus and ada pts to provide an environment that permits the establishment of pregna ncy. We used large-format two-dimensional (2D) PAGE to analyze the dyn amic changes in protein composition of uterine luminal fluid (ULF) dur ing this stage of pregnancy, and we determined the contribution of eac h of the extraembryonic membranes and the endometrium to these changes . The majority of the more than 40 pregnancy-associated proteins in UL F at Day 17 were secreted by the conceptus. By 2D gel map comparison a nd Western blotting, we identified transferrin, secreted by the yolk s ac from Day 15, and cytoplasmic actin, one of the most abundant protei ns produced by the trophoblast at Day 17. Apolipoprotein Al and aldose reductase, whose abundance were markedly increased in pregnancy, were identified by peptide microsequencing. Aldose reductase, an enzyme re quired for the conversion of glucose to fructose, was shown to be synt hesized by the trophoblast, and its detection even before the formatio n of the placenta suggests that the synthesis of fructose may occur mu ch earlier than previously reported.