Transfer of Horseradish Peroxidase Across the Human Placental Cotyledon Perfused in Vitro
Physiological studies have indicated that the human placenta is to some degree permeable to macromolecules (Challier et al., 1985). The pathway and the cellular mechanisms by which this passage occurs are still not identified. Our previous investigations on the junctional pattern of the human villous trophoblast have suggested that the syncytium and the fetal capillary endothelium are the most important structures involved in placental transport (De Virgiliis et al., 1982; Sideri et al., 1983). Conflicting results have been reported by in vitro tracer studies either at capillary or at syncytial levels. In the human placenta incubated in vitro with HRP conjugated IgG, Lin (1980) detected the protein in the inter-endothelial space and in the transcytotic vesicles of the fetal capillary, while King (1982) observed the reaction product only in transcytotic vesicles. Both authors were unable to follow the endocytotic vesicles containing HRP conjugated IgG in their trophoblastic pathways. In animal studies, Kaufmann et al. (1982) have suggested that transtrophoblastic channels, detected under perfusing conditions of fluid-shift, are involved in the transfer of HRP. Sibley et al. (1981, 1983) failed to demonstrate any uptake of HRP into the syncytium. These two authors showed a passage of HRP through the fetal capillary endothelium via the inter-endothelial spaces. In addition, Firth et al. (1983) indicated that the junctional complexes between two adjacent endothelial cells are capable of some selection, at least for the charged molecules.
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