Few specific activities have been especially attributed to the type 2 IGF receptor. However, stimulation of mesenchymal stromal cell and cytotrophoblast proliferation by IGF-II in the first trimester of gestation, together with the presence of IGF-II receptors on the villous cytotrophoblast, strongly suggests that IGF-II has an autocrine and/or paracrine action to control the growth of the placenta in relation to other peptides (endothelins). The IGF-II system is important in mice, since mice lacking IGF-II receptors die at birth (see for review). flovent inhaler
Hence, whatever the role of IGF-II receptors in the human placenta, they must also be important. But the differential distribution of receptors on the two membranes of the syncytiotrophoblast has not been explained. We do not yet know which side of this epithelium is the main side for the IGF-II pathway at the end of gestation. We also have no idea of the reason for the asymmetrical distribution of the type 2 IGF receptors on the two membranes of the trophoblast. Whether the differences in the two Kd may account for a dominant activity according to the location of the receptor on the trophoblast is a hypothesis we cannot yet confirm. Clearly, further work is needed to answer these questions and to build a clearer picture of the way in which development of the fetal-placental unit is regulated.