It has been hypothesized that fluid shear stress, induced by the flow of interstitial fluid, mediates the response of bone to loading and mediates modeling/remodeling. In vitro studies have demonstrated that bone cells are stimulated by fluid shear stress, and respond with the release of nitric oxide (NO) and prostaglandins. The in-vivo relevance of interstitial fluid flow (IFF), however, has yet to be established of the proposed research is to characterize three models of altered IFF in the absence of mechanical strain, and determine the role of nitric oxide and prostaglandins in IFF induced bone modeling/remodeling. Specifically, (1) we will characterize the effects of altered IFF induced by femoral vein ligation on histomorphometry, femoral dimensions, mechanical properties, mineral content, and mineral density in hindlimb suspended mice and rats; (2) we will determine the role of NO and prostaglandins if IFF-mediated modeling/remodeling by using genetically engineered mice lacking nitric oxide synthase 2 (NOS2), nitric oxide synthase 3 (NOS3), and cyclooxygenase 2 (COX2); (3) We will develop an externally applied cuff to alter IFF in bone as the first step in the clinical application of the findings. We will seek to optimize the regime of cuff pressure application and the duration of treatment to increase bone; (4) to further validate that IFF is altered in our rat models, direct measurements of IFF by magnetic resonance imaging will be performed. The long-term goal is the development of non- pharmacological methods to counter osteopenia of disuse.
