Two of the three sets of binding sites for 125I-IGF-II on the two trophoblast membranes are links in the chain of a regulation system. One is the insulin system. In the first trimester of gestation, the fetal-placental insulin system is under the mother’s control; it moves to the control of the fetus at the end of gestation when, interestingly, there are more receptors on the membrane that bathes the maternal blood in the intervillous space than on the membrane that faces the fetus. buy ortho tri-cyclen
Therefore the number of insulin receptors on each of the two membranes does not necessarily reflect their relative importance in their regulating function(s). The second system is the IGF-I regulation system. The infant’s birth weigh correlates with cord blood IGF-I but not with IGF-I in the serum of the mother. This suggests that there are two independent ways of regulating IGF-I in the two circulation systems, the most important for metabolism being represented by the smallest number of receptors. We believe this indicates the existence of metabolic adaptation of the two membranes of the trophoblast facing two independent circulation systems: the trophoblast seems to behave like a polarized epithelium.