The Uptake of Iron in R a B B I T Synovial Tissue Following

Iron dcxtran (molecular weight 7,000) diffuses rapidly from the joint cavity through the synovium, along lymphatics and cxtraccllular tissuc spaces; articular cartilagc is impermeable to iron dextran. Thcre is also rapid cellular uptake by synovial lining cells, particularly of the vacuolar type; cndoplasmic reticulum-containing lining cells rarely take up iron dextran. Cellular uptake is probably effccted by pscudopodial folds projecting from the cell surface and enclosing cxtraccllular material. Cells containing iron may degcncrate and be ingested by phagocytes, and this may account for the concentration of iron in a smaller proportion of cells on or below the synovial surface in the latcr stages. At 6 to 18 hours after injection there is a mild inflammatory reaction and some synovial proliferation; from this stage onwards intracellular iron occurs in the form of haemosiderin. Granules of haemosidcrin are present in thc synovium 3 months after injcction and possibly longcr. I N T R O D U C T I O N The synovial membrane of the normal knee joint of the rabbit appears as a glistening, translucent layer less than 1 mm thick which lines the joint cavity and which is loosely or firmly bound to subjacent structures forming the joint capsule. Its general features closely resemble those of human synovial tissue as described for example by Barnett, Davies, and MacConaill (4). Histologically the membrane can be seen to consist of a finely fibrous tissue containing a prominent vascular bed. At the surface bordering the joint cavity there is an apparently discontinuous layer of cells (the synovial intimal or lining cells), the cytoplasm of which is often not clearly delineated by light microscopy from the neighbouring fibrous tissue. Apart from their position at the synovial surface, synovial cells are not readily distinguished morphologically from other connective tissue cells in the membrane but several workers have shown that intimal cells possess cytochemical properties and enzymatic activities which differentiate them from the fibrocytes of the stroma of the synovial membrane and subjacent capsular tissues (9, 20, 21, 31). The ultrastructure of synovial intimal cells has been studied by a number of workers (3, 13, 25, 26). Barland, Novikoff, and Hamerman (3) ob351 on Jne 2, 2017 D ow nladed fom Published August 1, 1964