Gestation-Stage Related Changes in the IGF System Components in the Equine Placenta.

The insulin-like growth factor (IGF) system regulates implantation, placental development, and angiogenesis in eutherian mammals. However, little is known about the changes in this system in equine placenta (chorioallantois; CA) and the endometrium (EN) during pregnancy, or the relationship to vascular endothelial growth factor () expression. The current study investigated the expression of the IGF system components, namely the ligands ( and ), their receptors (, , and ), and their binding proteins ( and s) in equine CA at 45 days, 4, 6, 10, and 11 months of gestational age (GA) and immediately postpartum (PP), and in equine EN at 4, 6, 10, and 11 months GA. IGF1 immunolocalization and serum concentrations were also evaluated across gestation. mRNA expression in CA increased from day 45 to peak at 6 months and then gradually declined to reach a nadir in PP samples. This profile correlated positively with the expression profile (r = 0.62, = 0.001). In contrast, expression in CA was not correlated with ( = 0.14). Interestingly, mRNA was more abundant in equine CA than ( < 0.05) throughout gestation. Among the IGFBPs investigated in CA, the expression of and was highly abundant ( < 0.05) at day 45 compared to other GAs. Conversely, mRNA expression for and was more abundant ( < 0.05) in PP than at all investigated GAs. Immunohistochemistry revealed that IGF1 is localized in the equine chorionic epithelium (cytoplasm and nucleus). IGF1 serum concentrations peaked at 9 months and declined to their lowest levels PP. In conclusion, this study demonstrates a positive correlation between and expression in equine CA during gestation, suggesting that the IGF system plays a crucial role in placental angiogenesis by regulating .