It is not known if one or many exchange tissues are involved in regulating the extracellular fluid volume in the mouse conceptus. It is unlikely that the number of cells is a major determinant. There is only a 15% decrease in the DNA content of the placenta + fetus at a time when the cavities are reduced by 25% (Table 1). For a similar reason, it is also unlikely that the cell numbers of the fetal placentas are decisive in regulating these volumes. When there is a minor and nonsignificant reduction in the DNA content of this fraction (Table 5, ICM series), then the volume of the cavities is reduced by 25% (Table 3). We therefore favor an explanation of the effects of IGF-2 deficiency based on its physiological functions. buy cheap antibiotics
IGF-2 might control fluid uptake by a direct action on the maternal capillaries. Currently, only IGF-1 is known to increase fluid movement from the capillaries to the extra-vascular spaces, with increased capillary permeability and increased ‘‘filtration’’ following increased blood flow as the probable mechanisms. It is probable that IGF-2 has a similar effect because both the IGFs are potent inducers of vascular endothelial growth factor (VEGF) mRNA and protein, and VEGF increases capillary permeability as well as promoting angiogenesis. Further, IGF-2 stimulates angiogenesis in both the chorioallantoic membrane and rat cornea assays. The maternal and fetal circulatory systems in the placenta provide extensive surfaces for these local actions.