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Gravitational Effects on Glucose Diffusion into Cartilage Tissue.   R.E. Flowers-Aime¹, C.M. Marshall¹, A.W. von Deutsch^2,3, A.A. Belton², J. Wright⁴, D.A. von Deutsch², D.F. Paulsen¹ and B.J. Klement¹  Depts. of ¹Anatomy & Neurobiology and ²Pharmacology & Toxicology, ³Clinical Research Center, Morehouse School of Medicine, Atlanta GA, ⁴Auburn University.

   Cartilage has the ability to bear mechanical stress without distortion. It is avascular, so nutrients and oxygen must diffuse through the extracellular matrix to reach the cells. Changes in nutrient availability could alter cell metabolism and ultimately cartilage structure and function. The objective of this project was to determine if glucose diffusion into cartilage was altered in a microgravity (MG) or hypergravity (HG) environment compared to controls at standard 1x gravity (1xG). The experiments were conducted in parabolic flight aboard the NASA C-9 aircraft. A flight-certified apparatus consisting of three interconnected syringes contained each experiment on the aircraft. Bovine articular cartilage was exposed to a fluorescent labeled glucose solution for 20 seconds during the MG, HG or 1xG episodes during flight. The amount of glucose that diffused into the tissue was quantitated. There was no significant difference in the wet or dry weights of the samples. The total amount of glucose that diffused into cartilage during MG and HG was significantly less than at 1xG by 23% and 27%, respectively. The amount of glucose per tissue wet weight was reduced in the samples exposed to MG and HG compared to 1xG controls, but they were not significant. However, the amount of glucose per tissue dry weight was significantly less in the MG (26%) and HG (41%) samples than at 1xG. Tissue fluid volume may not be as important for diffusion in MG and HG as the structural components of the matrix. Since diffusion is reduced in both MG and HG, two different mechanisms, such as matrix conformation and tissue fluid flow, may be responsible. This suggests that cartilage nutrition may be impaired in different gravitational environments.  Supported by NASA grants NCC9-112, NAG3-2611 and RGSFOP at JSC, as well as RR03034 and NCRR 5P20RR11104.