An extensive lysosomal system in the maternal epithelium of the porcine placenta.

The material comprised 64 placentae from 19 Danish Landrace sows representing gestational stages from 16 to 112 days. The maternal epithelium was examined by means of light and electron microscopy to describe the morphology of the irregular electron-dense bodies and membrane whorls and their relation to gestational stages. Incubation for acid phosphatase demonstrated their lysosomal nature. Electron micrographs of serial sections followed by reconstructions and freeze-fracturing demonstrated their three-dimensional structure and relation to transfer tubules. In the early stages, during the development of fetal vascularization, the maternal epithelium was dominated by inclusions of lipids and glycogen, which can easily be transferred to and utilized by the embryo. The development of an extensive lysosomal system, consisting of irregular electron-dense bodies, membrane whorls and transfer tubules, indicates that cellular digestion is an important factor in the transfer and subsequent fetal utilization of maternal nutriments in the last two-thirds of gestation, and that this development is apparently related to anatomical and physiological changes during gestation.