Fat-deficiency disease of rats. The relative curative potencies of methyl linoleate and methyl arachidonate with a note on the action of the methyl esters of fatty acids from cod liver oil.

IN a previous communication [Hume et al. 1938] experiments were described in which the relative potencies of methyl linoleate and Jinolenate in curing the fat-deficiency disease of rats were determined. The finding of Burr et al. [1932] was confirmed that the presence of either of these acids in a fat-free diet is able to promote the weight increase of rats but, in contrast with the results of Burr & Burr, it was found that linolenic acid had only about one-sixth of the potency of linoleic acid. The highly unsaturated acids which have so far been shown to be characteristic of animal fat are tlhe C20 acid (arachidonic) with 4 double bonds, and the C22 acid with 5 double bonds; it was shown by Nunn & Smedley-MacLean [1938] that arachidonic acid was absent from the livers of rats which had been fed for about 7 months on the fat-deficient diet, but was present in those which, after such a depletion period, had received for 5 weeks a daily dose of 14 mg. methyl linoleate. Investigation of the activity of arachidonic acid was therefore of interest. Two apparently conflicting statements as to its biological activity appear in the literature. Burr et al. [1932] replaced 10% of a mixture of methyl linoleate and linolenate by methyl arachidonate, and found that the mixture containing the arachidonic acid was less effective than the original mixture. Turpeinen [1938], on the other hand, working in Evans's laboratory, claimed that methyl arachidonate was 3 times as potent as the linoleate in promoting weight increase, but he gave no detailed account of its effect on the skin condition. An investigation of the comparative effects of methyl linoleate and methyl arachidonate has therefore been carried out and is now described. The results appear to establish conclusively the superiority of methyl arachidonate in promoting weight increase but not in curing the skin lesions.