The Effect of Severe Dietary Protein Restriction on Skeletal Muscle Fiber Number, Area and Composition in Weanling Rats

Abstract

The purpose of the present investigation was to determine the effects of severe dietary protein restriction on soleus (S) and tibialis anterior (TA) fiber number and S muscle fiber area, composition and length. The S and TA muscles were removed from one leg of 12 male Sprague-Dawley rats at 21 d of age. Six of these animals were placed on a 1% protein diet until 42 d of age, while six served as age-matched controls. Muscle fiber number was determined by the nitric acid digestion method for S muscles and the mean fiber dry-weight estimation method for the TA muscles. Mean fiber numbers for the S muscles were 2,655 ± 42 and 2,669 ± 71 for the treatment group at 21 and 42 d of age, respectively, and 15,989 ± 899 and 16,067 ± 695 at 21 and 42 d of age, respectively, for the TA muscle. For the age-matched control group, fiber numbers for the S muscle were 2,928 ± 78 and 2,949 ± 76 at 21 and 42 d, respectively, and 17,964 ± 281 and 18,445 ± 296 at 21 and 42 d, respectively, for the TA muscle. The S muscle fiber area, composition and length were studied using 12 male Sprague-Dawley rats. Six animals were placed on the 1% protein diet from 21 to 42 d of age, while six animals served as age-matched controls. The S muscle fiber area was 33.1 and 51.5% smaller for type I and type II fibers, respectively, for animals fed the 1% protein diet. The S fiber length was 27.9% less in animals fed the 1% protein. Type I fiber composition was not different between the two groups. The results of this study indicate that severe dietary protein restriction results in a decreased rate of muscle growth that is a result of a decreased growth rate of the individual muscle fibers with no decrease in muscle fiber number.

© American Society of Animal Science 1985