BOVINE ENDOMETRIAL RETINOL-BINDING PROTEIN SECRETION, MESSENGER-RIBONUCLEIC-ACID EXPRESSION, AND CELLULAR-LOCALIZATION DURING THE ESTROUS-CYCLE AND EARLY-PREGNANCY

Retinol-binding protein (REP) mRNA was localized to luminal and glandu lar epithelial cells of bovine endometrium by in situ hybridization. R elative levels of endometrial RBP mRNA expression during the estrous c ycle and early pregnancy were determined by quantitative slot blot ana lysis and contrasted with uterine luminal concentrations of RBP. Expre ssion of mRNA was moderate at Day 1 after estrus, declined at Day 5, r eached lowest levels by Day 10, rose significantly through Days 15-17, and peaked at Day 20. RBP mRNA expression in pregnant animals was sim ilar to that in cyclic animals on Day 15, doubled between Days 17 and 20, remained constant through Day 22, and rose slightly thereafter. Lu minal RBP concentrations of cyclic cows, as determined by ELISA, decre ased from Day 1 through Day 10, rose dramatically on Day 15, then decl ined through Day 20. Concentrations of RBP in uterine flushes from pre gnant animals were similar to those of cyclic cows on Day 15 but remai ned relatively constant through Day 17. It is concluded that 1) RbP sy nthesis occurs in the luminal and glandular epithelial cells, 2) RBP t ranscription and secretion are correlated with each other, and 3) ovar ian steroids, possibly in conjunction with uterine concentrations of t heir receptors, modulate uterine RBP expression.