Immunohistochemical Localization of Insulin-Like Growth Factor-I (IGF-I) and IGF-I Receptor in the Human Placenta

The placenta is a fetal organ which has multiple functions. Insulin-like growth factor-I (IGF-I) has been demonstrated to be involved in fetal growth. Immunohistochemical localization of IGF-I and IGF-I receptor (IGF-I-R) was compared to expression of Ki-67, a proliferating marker in the chorionic villi of human placenta. Fresh frozen blocks were prepared from 11 chorionic villi and placentae obtained at early gestation (6～10 wk) and term delivery (37～41 wk), respectively. Staining was performed by a streptavidin-biotin method using monoclonal antibodies against IGF-I, IGF-I-R and Ki-67. IGF-I was strongly expressed on endothelium in all specimens examined. IGF-I-R was localized on the cell membrane of cytotrophoblasts and the apical membrane of syncytiotrophoblasts in villi in all specimens, and was also localized to villous endothelium at term. Ki-67 expression was strongly detected only in cytotrophoblasts in the villi at early gestation, and this staining co-localized with IGF-I-R staining. Spatial and temporal changes in the immunohistochemical localization of IGF-I-R in human placental villi that was co-localized with or without Ki-67 suggests that IGF-I is involved in the regulation of both placental metabolism and proliferation