SECRETORY AND MORPHOLOGICAL-CHANGES IN THE BABOON (PAPIO-ANUBIS) UTERUS AND PLACENTA DURING EARLY-PREGNANCY

The study was undertaken to characterize changes in uterine endometria l secretory activity and morphology in the baboon between Days 18 and 32 of pregnancy- Proteins synthesized by the implantation site endomet rium (RI) and non-implantation site endometrium (RIII) and developing placenta were analyzed by two-dimensional PAGE and fluorography. The e lectrophoretic mobility and localization of chorionic gonadotropin (CG ) in the baboon placenta, and insulin-like growth factor binding prote in-1 (IGFBP-1) and retinol binding protein (RBP) in the baboon uterus were confirmed by Western blot analysis and immunocytochemistry. Place ntal protein synthesis was primarily characterized by the presence of radiolabeled CG at Days 18 and 25, which decreased by Day 32. Peak CG synthetic activity, immunolocalized to the syncytiotrophoblast, occurr ed during the formation of tertiary villi. Also associated with the de velopment of mature villi was a corresponding increase in a basic prot ein (M(r) 23000). The overall secretory pattern of the baboon endometr ium was similar to that observed during the midluteal stage; however, the synthetic activity was enhanced during pregnancy. Radiolabeled and immunoreactive IGFBP-1 and RBP were detectable in the Day 32 function alis and basalis, respectively, and their synthesis was higher in RI c ompared to RIII. The immunolocalization of IGFBP-1 in RI appeared to b e directly related to the degree of decidualization. In addition, a no vel group of low molecular-weight (M(r) 27000-30000) isoelectrovariant proteins was secreted predominantly by the basalis at Days 18 and 25 of pregnancy and disappeared by Day 32 in all but one animal. The synt hesis of this group of proteins did not show regional specificity. The se studies indicate that the baboon endometrium undergoes morphologica l and secretory changes during pregnancy that are associated with the development of a functional placenta and decidualized endometrium. Fur thermore, these studies suggest that the conceptus/placenta may mediat e specific changes in IGFBP-1 and RBP expression at the implantation s ite.