Immunolocalization of insulin-like growth factor I (IGF-I) during preimplantation in rat uterus

ObjectiveThe aim of this study was to determine the insulin-like growth factor (IGF-I) immunolocalization in rat uterus at preimplantation period.DesignThe tissue samples were examined from pregnant animals between gestational day 1 and 5 using immunocytochemistry.ResultsWhile both the uterine luminal epithelium and the glandular epithelium were stained strongly from gestational day 1--3 by IGF-I antibody, the IGF-I immunoreactivity was moderate in myometrium and capillary endothelium. At this period, the IGF-I immunoreactivity was weakly present in a few endometrial stromal cells. At day 4, while IGF-I immunostaining intensity was particularly decreased in the basal domains of uterine luminal epithelium and glandular epithelium, it was similar to the first 3 days of gestation in myometrium and capillary endothelium. The endometrial vascularization and the number of stromal cells immunoreacting with IGF-I increased. The differentiation of stromal cells into decidual cells was seen at gestational day 5 and IGF-I was strongly expressed in the decidualizing cells. The IGF-I immunoreactivity in uterine luminal epithelium and glandular epithelium was similar to gestational day 4. IGF-I immunoreactivity was strongly detected in all of endometrial stromal cells.ConclusionThese results indicate that IGF-I expression in the rat uterus changes in the early pregnancy process and increase toward to day when implantation will be initiated.