ASGSB 1999 Annual Meeting Abstracts

THE EFFECT OF UNLOADING ON RAT METATARSAL. S.B. Arnaud¹, R.E. Grindeland¹, A. Bigbee¹, M. Yamaguchi². ¹Life Sciences Division, NASA Ames Res. Center, Moffett Field, CA and ²Dental Res. Center, Univ of North Carolina, Chapel Hill, NC.

Exposure of rats to a space flight model which unloads the hindlimbs regularly causes lower mineral content in the major weight-bearing bones.  Effects on the bones of the foot are uncertain and the aim of this study. Animals were mature male Sprague Dawley rats housed in single cages and fed Purina chow containing 0.56% calcium and 0.58% phosphorus. Controls (C) were fully ambulatory.  Rats with hindlimbs unloaded by tail suspension (S) had paws 1 cm above the plastic 1/2”grid floors. After 0,1,4 and 8 weeks, animals were killed.  The right soleus muscle was removed and weighed. The 3rd metatarsal from the right foot was removed, cleaned of soft tissue, dried @ 110C for 24 hours and then ashed @600C for 24 hrs to estimate mineral content (BMC).  After 8 weeks, BW were lower in S than C, 388±22g vs. 437±12g, p<.001.  The right soleus in S was half the weight of the muscle in C (84.6±15 vs. 170.5±57, p=.001). BMC in the metatarsals of S were the same as in C bones (B:30.6±1.4, 1wk:29.5±1.5, 4wk:30.5±1.01 and 8wk:30.7±1.3 mg).  The lack of osteopenia in the unloaded metatarsal was unexpected, especially considering the evidence of disuse with muscle atrophy in same limb.  This result may be due to low bone turnover, the architecture of the floor or other unknown factors.

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