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DOI: 10.1055/s-2007-983471
Transvascular permeability in the blood vessels of the human placental cotyledon
1. Aims:
The placental cotyledon contains an integral vascular circulation which includes arterial, capillary and venous segments. This vasculature is described as fetal, it nonetheless mediates well-differentiated transport functions involving selective exclusion of some substances and uptake of others. The permeability of the cotyledon vessels varies according to developmental stage and is under hormonal and growth factor control. We used fluorescence microscopy to analyse passage of perfused proteins across the cotyledon vessel walls.
2. Methods:
Cotyledons obtained at elective term cesarean sections were perfused with buffered saline containing test protein: tomato lectin (Lycopersicon esculentum agglutinin, LEA) conjugated with fluorescein (FITC) fluorescent dye. The test protein was circulated via a cannula in one of the larger vessels for periods of a few minutes, then the cotyledon was shock-frozen in isopentane cooled in liquid nitrogen. Frozen sections of 15µm thickness were freeze-dried, heat-fixed, then incubated with 10mg/ml of LEA conjugated with rhodamine (TRITC) fluorescent dye. Sections were viewed by fluorescence microscopy.
3. Results:
Endothelial cells labelled strongly red in the fluorescence microscope, due to binding of the LEA to polylactosamine chains of the endothelial glycocalyx. Some vessels, of large diameter, were surrounded by haloes of green fluorescent material, representing LEA-FITC perfused into the living cotyledon extravasating from them. Small-diameter vessels exhibited well-demarcated edges and stood out clearly against the black background.
4. Conclusion:
The arterial and/or the venous segments of the cotyledon vasculature include stretches of vessel which during a relatively short incubation period permit passage of the LEA molecule, with molecular weight 68 kiloDaltons. These vessels are therefore quite permeable. The capillary segments of the vasculature were not observed to exhibit this permeability for a large protein molecule.