EFFECTS OF SUSPENSION HYPOKINESIA HYPODYNAMIA ON THE BODY-WEIGHT AND NITROGEN-BALANCE IN RATS FED WITH VARIOUS PROTEIN CONCENTRATIONS

Hypokinesia/hypodynamia was induced in the hindlimbs of rats by means of a suspension harness, and metabolic balance studies, especially regarding nitrogen, were performed with different dietary protein levels (5, 10, 20, 40 and 60 % casein diets). During a 10-day period of hypokinesia, significant reductions in the food intake and body weight were observed, especially with the high protein (60 % casein) diet. However, the total nitrogen balance was positive (only in the first 1-2 days was the nitrogen balance negative in the suspended rats fed with the low-protein (5 % casein) diet), even with the 5 or 10 % protein diet, and the body protein content was also increased, as compared with that in the non-suspended rats. On the other hand, as a significant decrease in body fat was observed, the loss of body weight may have been mainly due to this fat decomposition. Hindlimb muscle atrophy (gastrocnemius and soleus) and also adrenal hypertrophy were observed. It may be considered that suspension causes glucocorticoid-mediated muscle catabolism. These results show that significant muscle atrophy and parallel changes in nitrogen metabolism occur in suspended rats, and an investigation of the mechanism underlying these changes by suspension may provide a new approach for crew health in space flight or to a solution of the many different problems from prolonged bed rest. © 1990 by the Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.