Secretory proteins of the baboon (Papio anubis) endometrium: regulation during the menstrual cycle and early pregnancy

Abstract

The biological function of uterine endometrial secretory proteins in the primate remain to be elucidated. In general, during the luteal phase and under progesterone dominance, the glandular epithelial cells synthesize and secrete a number of proteins. Of these, placental protein 14 (PP14; now referred to as glycodelin) and insulin-like growth factor binding protein-1 (IGFBP-1) are the best characterized. Although induced by progesterone, their synthesis increases exponentially during pregnancy. In the baboon, glycodelin is immunolocalized to the mid functionalis and basal glands between days 10 and 12 post-ovulation. In response to either exogenous or blastocyst-secreted chorionic gonadotrophin, glandular synthesis increases markedly and remains elevated up to days 18-25 of pregnancy. The decrease in glycodelin in the endometrium is associated with glandular regression during the first third of pregnancy. In contrast, IGFBP-1 is only observed in the deep basal glands during the luteal phase. Following the establishment of pregnancy, IGFBP-1 synthesis switches from glandular to stromal and is correlated with the process of decidualization. IGFBP-1 synthesis continues to increase throughout gestation. We propose that glycodelin may have immunosuppressive properties and that IGFBP-1 may regulate trophoblast migration within the uterine endometrium.