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Nutrient diffusion through articular cartilage: development and use of a model system. C.M. Marshall, RE. Flowers, N. Goli, M. Vandromme, D.F. Paulsen, B.J. Klement Dept. of Anatomy/Neurobiology, Morehouse School of Medicine, Atlanta, GA.

   Cartilage is avascular, so nutrients and oxygen must diffuse through the extracellular matrix to reach the cells.  Changes in the physical properties of cartilage matrix can disturb the maintenance of normal cartilage function.  The goal of the current project was to develop a model system to evaluate nutrient diffusion in articular cartilage and use this model to assess diffusion in cartilage from hindlimb unloaded (HLU) rats.  Sections (50m) were cut from bovine articular cartilage and incubated in fluorescent labeled glucose (2-NBDG). The sections were then placed in aliquots of PBS for 1-minute intervals and the 2-NBDG that diffused out of the sections was collected and measured.  A concentration of 50M 2-NBDG gave a level of fluorescence that could be quantitated.  A soaking time of 1 hour was sufficient for maximum glucose incorporation into the cartilage sections. Rat tibias were cleaned of soft tissue and the cartilage from the tibial plateaus were cut in 40m sections.  After soaking in 2-NBDG, the amount that diffused from the sections was collected and quantitated.  The 2-NBDG from sections isolated from rats that had been HLU for 7 days showed no significant difference from the controls. The 2-NBDG that diffused from sections obtained from rats HLU for 21 days was significantly less (31% and 48%) than from controls.  There was no significant difference in the percent of tissue fluid in sections from HLU and control rats.  Although the data was not statistically different, the amount of 2-NBDG normalized to tissue dry weight was 36% less in the sections from HLU rats than from controls.  Furthermore, 2-NBDG diffusion from sections that were removed from the lowest 80m in the cartilage was 55% less than in sections removed from the upper 80m in the HLU rats.  There was no significant difference between these levels in the control rats.  The lower 80m sections in the HLU rats had 67% less 2-NBDG than the lower sections of the controls.  HLU results in a change in nutrient diffusion, possibly by altering the cartilage architecture. (Supported by NASA grants NAG3-2611 and NCC9-112 as well as RR-03034.)