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Responses of Body Composition and Hematological and Muscular Properties of Meriones Unguiculatus to Gravitational Unloading.  Y. Nakajima¹, M. Terada², F. Kawano³, H. Sumi³, Y. Shimizu³, T. Ohira², Y. Higo², X.D. Wang³, N. Nakai³ and Y. Ohira^{2, 3}.  ¹Sch. of Sci., Grad. Sch. of ²Frontier Biosci. and ³Med., Osaka Univ., Toyonaka City, Osaka, Japan. 

   Effects of 14 days of hindlimb suspension (HS) on the body composition and hematological properties were studied in 9-wk old male meriones unguiculatus, since the responses of these properties in this animal are not fully studied.  The food and water were given freely during the experiment.  Red blood cell counts, hemoglobin concentration and hematocrit levels were increased due to hemoconcentration (lowered water content) after HS.  White blood cell and platelet counts were lowered, on the contrary.  Significant atrophy was noted in soleus and adductor longus muscles, although the mass of other hindlimb muscles were stable.  The weights of adrenal and thymus, measured as the stress markers, were not different from controls.  Further, the mass of other organs, such as brain, heart, liver, kidney, and spleen, were not influenced by HS, either.  Even though food intake was similar to the control, water consumption was very low during HS.  This phenomenon may be the major cause for the hemoconcentration.  However, the increased blood viscosity and/or possibility of clot may be modified by lowered platelet counts.  The % water content of muscle in control animal was less than other species and the unloading-related water loss from plantaris muscle was also less than others.  These phenomena may be closely related to the greater tolerance to dehydration in this animal.  It was suggested that meriones unguiculatus could be one of the unique animals to be used for spaceflight experiment. (Supported by the Grant-in-Aid for Scientific Research (S, 19100009) from Japan Society for the Promotion of Science)