INACTIVITY CHANGED FIBER-TYPE PROPORTION AND CAPILLARY SUPPLY IN CAT MUSCLE

The effect of different levels of activity on fiber types, capillaries and enzymes of gastrocnemius and soleus muscles was studied in two gr oups of cats. The first group was successfully kept in a large room, e xercised on a treadmill 15 min daily 5 days per week and kept in indiv idual small cages. Each period lasted 6 weeks. A muscle biopsy was tak en after each period. The second group was formed by cats that were ca ged for over 20 months. In the group caged for over 20 months, gastroc nemius muscle showed higher IIB and lower I fiber type proportion. Fib er cross-sectional area was not different in any condition. All capill ary measurements were significantly lower in gastrocnemius muscle of l ong-term caged cats, and capillaries per mm(2) were lower in soleus mu scle of these cats. Exercise increased capillary/fiber in soleus muscl e but subsequent caging did nor reduced it. In soleus muscle, beta-hyd roxy-acyl-CoA dehydrogenase levels decreased after the cage period and hexokinase levels increased after the exercise and decreased after th e cage period. In conclusion, different levels of activity for short t ime produced enzyme changes in soleus muscle, whereas long-term inacti vity changed fiber type proportion in gastrocnemius muscle and reduced capillary supply. (C) 1997 Elsevier Science Inc.