Effects of Fat-Free Diet on Histological Fats in Various Organs of the Rat

Abstract

It has been shown 1 that rigid exclusion of fat from the diet of the rat induces a characteristic deficiency disorder, since the animal is apparently unable to synthesize certain fats which are necessary. The present study was undertaken to determine whether the histological fat distribution in the various organs is affected in this disorder. The organs studied include the liver, kidney, trachea, lung, skin and tela subcutanea.

Through the courtesy of Doctors Burr and Brown, 26 typical test rats that had been maintained several months on the fatless diet (No. 550B, plus vitamin supplements) were available, together with 5 rats “cured” by the subsequent addition of the necessary fats to the diet. These rats were killed by chloroform and autopsied in the usual way. The fats were studied chiefly in formalin-fixed, frozen sections stained with a solution of “oil red O” in diacetin (which presumably stains all fats and lipoids), though in some cases other methods were used. The technique is explained in detail in a separate paper dealing with the normal distribution of fats at various postnatal stages in the rat. 2 Both test rats and controls were females of the Wistar strain.

For comparison, 3 types of controls were used. (1) Eleven direct controls were reared on the same fatless diet (550B) with the addition of the necessary vitamins and fat. This is a high carbohydrate diet, containing 84% sucrose. (2) Eight stock diet controls were reared on our normal colony diet (McCollum's diet I), containing 67.5% ground wheat, 15% casein, 10% whole milk powder, and 5.2% butter-fat. (3) Since the test rats were retarded in growth and somewhat emaciated, 5 inanition controls were held by simple underfeeding of the stock diet at a body weight corresponding to that of the test rats.