Fat-deficiency disease of rats. The effect of doses of methyl arachidonate and linoleate on fat metabolism, with a note on the estimation of arachidonic acid

Abstract

The % of neutral fat and phospholipin calculated on the wet wt. of tissue in the liver, muscle and kidney of rats kept for 215 days on a fat-free diet showed no significant variation when compared with similar figures for rats which after 163 days of fat-free diet had received curative doses of linoleic and arachidonate for 5-7 wks. before being killed. In rats fed for 35 days with doses of arachidonate (1, 0.5 and 0.25 drop) and then returned to the fat-free diet, the liver lipid substance contained less phospholipin than in those in which the 1 drop doses had been continued. The muscles of rats which had received daily 1 drop doses of arachidonate and linoleate and had then been again fat-starved contained more fat than the muscles of rats which had received similar doses up to the time when they were killed. The tissues, especially skin and carcase, of rats which had received 0.5 and 0.25 drop doses of arachidonate for 5 wks. and had then been again fat-starved were much more fattened than those of rats which had received 1 drop doses of arachidonate or linoleate under similar conditions. The carcases of the 0.5 drop and 0.25 drop rats were also richer in phospholipin. The total wt. increase of 17 g. shown by the 4 rats receiving the 0.25 drop doses of arachidonate corresponded almost exactly with the excess fat found in their tissues. The 4 rats receiving the 0.5 drop doses increased by 69 g., of which only 19 g. were represented by excess fat. With the "1 drop" rats there was normal fat storage and much increase in wt. Arachidonic acid was absent from the neutral fat of rats fat-starved for 215 days but occurred in very small quantity in the liver and muscle phospholipins. The C20 hexabromide (M.P. 202-4[degree]) previously isolated from the liver lipin of rats kept for 257 days on the fat-free diet was not identified. The arachidonic acid stored in the organs of the rats receiving different doses of the unsaturated acids was estimated and compared with the intake of arachidonic acid. A minimum intake of arachidonic acid is necessary in order that the cells of the fat depots may first be loaded up with fat. Subsequently there is a process of true growth which is accompanied by the disappearance of comparatively large quantities of arachidonic acid. The changes in cholesterol metabolism were also detd. The method of estimating arachidonic acid by precipitation of the insoluble bromide is discussed.