Distinct Actions of Insulin-Like Growth Factors (IGFs) on Placental Development and Fetal Growth: Lessons from Mice and Guinea Pigs

Timeline of gestation in human, mouse and guinea pig with particular reference to timing of common stages of the placenta. The timing of IGF infusion and post mortem in the guinea pig experiments described in the text is also shown.

Schematic diagram representing IGF actions in the mother, placenta and fetus to enhance maternal adaptation to pregnancy and fetal and placental growth. IGF-I acts as an endocrine and autocrine/paracrine factor in the mother and fetus and as an endocrine factor in the placenta since its expression there is low in many species. It acts through the IGF1R. IGF-II acts as an endocrine and autocrine/paracrine factor in all three compartments. IGF-II exerts its effects through IGF1R, IGF2R, IR and a fourth as yet unidentified receptor XR.