Relation of the Essential Unsaturated Acids to Tumour Formation in the Albino Rat on Normal Diet by Ida Smedley-maclean and Leslie

RATS which have been fed from the time of weaning on a diet completely free from fat gradually cease to gain in weight, and after being thus dieted for from 4 to 6 months their weight remains constant. This condition is accompanied by other symptoms, of which a dry scurfy skin and the so-called scaly tail are the most obvious [Burr & Burr, 1930]. The animals can be cured by giving them small doses of linoleic or arachidonic acids, the latter being the most potent in promoting growth. The fat-starved rat which is receiving an unlimited diet of carbohydrate, protein and the necessary accessory factors, is still able to make and store fat; indeed, the proportion of fat in rats after a very long period of fat-starvation was found to be exceptionally high [Smedley-MacLean & Nunn, 1940; Hume et al. 1940]. When daily doses of 7-14 mg. methyl arachidonate were given to rats which, had been for many months on a fat-free diet, growth was resumed and analysis of the carcass 5 weeks later showed that the increased weight was accompanied by a diminution of the proportion of fat present when compared with animals which were still receiving only the fat-free diet. It was also observed that only a fraction ofthe arachidonic acid which had been administered was found in the body [Smedley-MacLean & Nunn, 1940]. The part played by the highly unsaturated acid does not appear therefore to be concerned with the formation of fat from carbohydrate or with its storage. It does, however, play some essential role in bringing about an increase in weight which is not due to the deposition of fat and which probably therefore involves the formation of new cells. The diminished store of fat found in the carcass and subcutaneous tissue when curative doses of unsaturated acids were given suggested the possibility that, in the process of growth, this diminution of fat might be directly connected with the formation of new tissue, and that the process might possibly be in some way linked up with the part played by these essential unsaturated acids. We desired therefore to investigate the changes in the content both of fat and of highly unsaturated acid in some other condition where the formation of new cell tissue was actively proceeding. Such a condition is provided by the rapidly growing Walker tumour grafted under the skin of the rat. We therefore enlisted the co-operation of Dr Haddow to whom we are greatly indebted for providing us with the necessary material. The rats selected were 100-150 g. in weight and were fed throughout the experiment on a diet rich in fat; it contained milk, oil cake and fish-meal so that there was a good supply of unsaturated acids. Generally speaking, in 10-14 days