Studies on the linoleic acid contents in the phospholipids of the sarcoma.

Abstract

In order to find the reason why there is only a small amount of linoleic acid in the unsaturated fatty acids fraction of phospholipids in the tumor tissue, the authors have made studies about this point on the transplanted sarcoma and neighboring normal muscle tissues of the rats.1) The amounts of total unsaturated fatty acid in the phospholipids of the tumor and that of the normal muscles are almost equal.2) The amounts of linoleic acid and linolenic acid of phospholipids of the tumor are of very small quantity compared with the amounts of that of the phospholipids of the normal muscles. Especially, the amount of linoleic acid is of remarkably small quantity.3) The mechanism under which the above phenomena appear can be thought of as follows:(a) The linoleic acid in the diet might be very difficult to be incorporated into the phospholipids of the tumor, or(b) The linoleic acid of phospholipids of the tumor might disappear at a more rapid rate than that of normal muscles.Investigating on these two factors, the authors obtained the following results:(A) When linseed oil is added to the diet and fed to the rats for 7 days, in- crease of the linoleic acid portion of unsaturated fatty acid of phospholipids of normal muscle is 5.44%, whereas that of tumor tissue is 13.83%.According to this result, the rate of incorporation of linoleic acid from the diet into the phospholipids is more rapid in the tumor tissue than in the normal muscles. The same result is obtained when the linseed oil diet is given for 4 days.(B) After the linseed oil diet is given for 7 days, then the fat-free diet is given from 1-7 days, and the tissues of these animals are analyzed. Results show that the linoleic acid of phospholipids of the normal muscles is not decreased even after 3 days and only a slight amount of decrease is noted after 7 days. However, on the fat-free diet, even after 1 day, the linoleic acid of phospholipids of the tumor shows some decrease, and on the 2nd and 3rd days the decrease is remarkable. According to this result, the disappearance of linoleic acid in the phospholipids is more rapid in the tumor than in the normal muscles.4) According to the above results, the amount of the linoleic acid in the phospholipids of the tumor is less than that in phospholipids of the normal muscles, not because of difficulty of incorporation of linoleic acid from the diet into the phospholipids of the tumor, but due to its rapid disappearance from the tumor tissue.