Ultrastructure of human placental tissue after 6 h of normoxic and hypoxic dual in vitro placental perfusion.

The dual in vitro perfusion model of human placental tissue allows the study of different aspects of placental function, such as metabolism, transport and secretion of proteohormones, cytokines and prostaglandins. The integrity of the perfused placental tissue is an important parameter to validate the perfusion system. Using light and electron microscopy, the morphology of villous tissue was examined before and after six hours of normoxic (n=10) vs. hypoxic (n=10) perfusion. An apical shift of the rough endoplasmic reticulum and occasional vacuoles were found in the syncytiotrophoblast of the terminal villi, the exchange area of the placenta. No unexpected pathological findings were seen before the perfusion experiments and only slight changes with moderate distension of the endoplasmic reticulum after 6 h of normoxic perfusion. After hypoxic perfusions, distinct ultrastructural alterations, such as oedematous villous stroma, swollen or completely destroyed cell organelles (e.g., mitochondria and endoplasmic reticulum), multiple vacuoles inside syncytio- and cytotrophoblasts as well as the microvilli were seen, which leads to an impairment of the placental barrier and other functions. The ultrastructural examination of placental tissue before and after dual in vitro perfusion broadens the knowledge of physiological and pathophysiological processes in the perfused placenta and may be a beneficial part of regular validation.

The anchoring zone in the human placental amnion: bunches of oxytalan and collagen connect mesoderm and epithelium.

This study deals with the examination of the elastic fibre system as well as collagen fibrils and collagen type IV in the amnion of the human chorionic plate of uncomplicated pregnancies at term. In organs other than placenta, the elastic fibre system comprises elastic fibres, elaunin and oxytalan microfibrils. The investigation was performed by light and electron microscopy and immunocytochemistry. Abundant oxytalan fibres were present in all amnionic layers, while no elastic fibres were found. Oxytalan microfibrils formed a broad sub-epithelial layer and were intermingled with collagen fibrils in the subjacent compact layer and in the amnionic mesoderm. Light microscopically, bunches containing orcein-stained oxytalan and collagen-type-IV-immuno-stained microfibrils were seen rising from the amnionic mesoderm perpendicularly towards the epithelial layer, where they obviously inserted. It can be assumed that the subepithelial microfibrillar layer and the following compact layer form an anchoring zone between the amnionic mesoderm and the epithelium that may contribute to the maintenance of strength. The ultrastructure of the bunches clearly showed collagen fibrils mixed with oxytalan microfibrils. No collagen type I-immunostaining was found in the bunches. After pretreatment of cryostat sections with elastase, oxytalan-orcein-staining was absent, but collagen type IV-immunoreactivity was not altered. Furthermore, after oxytalan-orcein-staining resp. anti-collagen type IV incubation, all positive fibres revealed an identical morphological pattern. We propose that oxytalan and collagen type IV may represent further members of the microfibril complex.