A comparative study of the lipid composition of white, intermediate, red and heart muscle in rats

The detailed lipid composition of white (rectus femoris), intermediate (soleus), red (diaphragm) and heart muscle isolated from fed and 48-h-fasted male rats was determined. 1. Contents of phospholipid and total cholesterol were high, with increasing levels of aerobic oxidation in muscles. Triacylglycerol content was highest in red muscle, moderate in heart and intermediate muscle and lowest in white muscle. 2. The molar percentages of phosphatidylethanolamine and cardiolipin were high and those of phosphatidylcholine, phosphatidylinositol and phosphatidylserine were low, with increasing levels of aerobic oxidation in muscles. 3. The molar percentage of alkenyl-acyl type was higher in phosphatidylethanolamine than in phosphatidylcholine which consisted predominantly of diacyl type. Heart and intermediate muscle had lower content of alkenyl-acyl type and higher contents of diacyl type in phosphatidylethanolamine as compared with white muscle, whereas the class composition in phosphatidylcholine were nearly the same among the muscles examined. 4. The contents of 18 : 0 in phosphatidylcholine and 18 : 0, 18 : 2 and 20 : 4 in phosphatidylethanolamine were high and those of 16 : 0 in phosphatidylcholine and 22 : 6 in phosphatidylethanolamine were low, accompanying approximately the increase in the levels of aerobic oxidation in muscles. The fatty acid composition of triacylglycerol was similar in all the muscles examined. 5. The fasting had little effect on the lipid patterns of the various types of muscles except for those of phospholipids in heart muscle. These results were discussed in relation to the cell structure and function for energy metabolism in various muscles.