[18]

BRIEF DAILY STRETCHING OF SOLEUS MUSCLES PREVENTS CENTRAL CORE-LIKE LESIONS IN HINDLIMB SUSPENSION UNLOADED RATS. D.V. Baewer, B.D. Curry, P.M. Reiser, J.L.W. Bain, R.H. Fitts, D.A. Riley.  Dept of Cell Biology, Neurobiology & Anatomy, Medical College of Wisconsin, Milwaukee WI, Dept of Biology, Marquette University, Milwaukee, WI.

   Hindlimb Suspension Unloading (HSU) is widely used to simulate the effects of microgravity unloading on the musculoskeletal system.   In a standing rat, the ankle joint is dorsiflexed at ~30 during weight bearing.  During suspension, gravity causes the hind feet to droop and open the ankle joint to ~90°.  This postural change decreases the working range (length) of soleus by 15-20% [Riley et al. JAP 69:58, 1990].  After 12 days, soleus muscle fibers exhibit atrophy and central core-like (CCL) lesions, which are characterized by focal regions lacking myofibrillar ATPase activity and sarcomere disruption at the ultrastructural level.  The present study sought to determine whether stretching the soleus muscle by bringing the ankle to 30° for 10 or 20 total min per day would prevent CCL lesion formation.  The left legs of suspended, male Sprague Dawley rats (261±6 g) were fitted with external plastic splints to hold the ankle at a 30° and stretch the soleus.  Four rats were splinted 10 min/day, and 5 animals were splinted 10 min twice a day.  After 12 days, the left and right soleus muscles were removed from anesthetized rats and quick frozen for cryostat sectioning and histochemical staining for acid (pH 4.35) and alkaline (pH 9.4) myofibrillar ATPase for detection of fiber types and CCL lesions.  Compared to the non-splinted side, the percentage of fibers with CCL lesions was less after treating 10 min (3.3±1.2% versus 27.5%±5) and 20 min (2.5±1.4% and 26.8±3.2%).   Lesions were most common in slow fibers.  These findings indicate that moving a muscle through its full working range is important for maintenance of sarcomere structure.  (Supported by NASA NAG9-1156) SPCDVB02