Previous research from this laboratory would suggest that immobilization induced by acute illness and bypassing the oral route of alimentation may account for the depressed bone formation and increased bone resorption observed in some patients dependent on parental nutrition. Because of the heterogeneity of human subjects underlying diseases, it is proposed to utilize a non-human primate model to study the interrelationship between the mode of nutrition support, immobilization, and bone formation and resorption. To test these interrelationships bone formation rates will be determined in animals fed orally versus animals fed intravenously and between those freely mobile versus those constrained by a jacket and tether system; serum from those animals will be tested for levels of essential bone hormones including parathyroid hormone and insulin-like growth factor 1; serum from test animals will be tested in vitro for its effect on bone formation and resorption; and osteoblast cells from test animals will be tested directly for proliferation and differentiation. The goal is to better understand one of the more prevalent complications observed in patients dependent on long term intravenous nutrition support, and to enhance our understanding of metabolic bone disease in general.