Compensation mechanisms for experimental reduction of the functional capacity in the guinea pig placenta. I. Changes in the maternal and fetal placenta vascularization.

After experimental reduction of its functional capacity, the placenta of the guinea pig has been studied microscopically for changes in the maternal and fetal vascularization pattern which could be interpreted as a compensation for this reduction. The functional capacity has been reduced in four ways. In the experimental groups the volume compared with untreated controls. The volume density of fetal capillaries in the labyrinthine part of the placenta was increased significantly compared with untreated controls. The surface density of these vessels, however, remained the same as in the control placentas. The volume density and surface density of the maternal lacunae did not change significantly. The conclusion is that after experimental reduction of its functional capacity the only structural modification in the guinea pig placenta involving the maternal and fetal vascularization, which can be interpreted as a compensation mechanism, is a widening of the fetal capillaries in the labyrinth.