A comparison of the response of thirteen muscles in the rat to dietary restriction

ABSTRACT

Information derived from a sample of a particular muscle or the entire muscle is often assumed to be characteristic of skeletal muscle in general. There has been little experimental work designed to validate this assumption which has important implications in clinical situations such as severe protein-energy malnutrition in which gross muscle wasting is a characteristic feature. This project was designed to gain information on the changes that take place in a number of muscles in the rat exhibiting severe muscle wasting following dietary deprivation. Eight male albino rats aged 5 weeks and weighing 100g were starved for 33 days and then fed a 1 percent protein diet for 20-22 days. Control animals were albino male rats of the same initial age and body weight. The 13 muscles examined were those of the trunk (rectus abdominis, diaphragm and psoas), thigh (gluteus), hind-limb (quadriceps, tibialis anterior, gastrocnemius and soleus), and fore-limb (Triceps, biceps, brachialis, Flexor carpi radialis and Extensor carpi ulnaris). Estimations on the whole muscle were made of wet weight, dry weight, fat free dry weight, cellular protein, extracellular protein, DNA and RNA. The results showed that the muscles of the experimental animals underwent similar compositional changes in response to the dietary restriction. The changes of four small fore-limb muscle were not characteristic at times. Overall the muscles lost 19 percent wet weight, 17 percent dry weight and 18 percent fat free dry weight. The total water content decreased by approximately 2 percent, cellular protein by 20 percent and total muscle RNA by 44 percent. Extracellular protein increased by 35 percent. There was no significant difference in the total DNA and fat content of nearly all the muscles of control and experimental animals. Although the muscles responded similarly to the dietary treatment the extent of change varied. Caution must be exercised when extrapolating these changes to the entire musculature (Summary)