Glycogen Formation in Rats

After a preliminary observation period on McCollum's stock diet I, adult rats were fed test diets containing about 87 per cent of the total caloric value in the form of sucrose, lard or casein, for about three weeks. The food and water intakes were determined during both the preliminary and the test period. The gain in body weight was evident on each diet suggesting adaptation. Without knowing the digestibility of each diet, and the absorptive power of each rat, it is difficult to interpret the changes in caloric intake during the test period. The water intake increased on the high casein diet, and decreased on the lard and sucrose diets. This is probably determined by the amount of nitrogenous waste products to be eliminated. The absolute liver weights were in close agreement on the various diets. Considered as per cent of body weight, the liver was lighter on the high lard diet and heavier on the high casein diet than on the control diet. Dry weights could not be determined. Liver glycogen was significantly higher on the high sucrose and significantly lower on the lard and the casein, than on the control diet. An exceedingly close relationship was found between the last twelve-hour food intake (grams) (8:30 P.M. to 8:30 A.M.) and the liver glycogen content, on the stock diet. The absence of such close agreement between late food intake and glycogen content on the sucrose diet suggested that in a liver already saturated with glycogen, more cannot be stored. Glycogen is probably not readily formed on a high lard diet, consequently it did not vary in accordance with the late food intake. There was some relation between the late food intake and glycogen content on the high casein diet. Either it is easier to form glycogen from casein, or the small amount of lactose present as an impurity in the crude casein is utilized. From the late intake, expressed as Calories per gram of body weight, and the glycogen content expressed as milligrams per gram of liver weight, we have worked out a glycogen formation efficiency scale. If our stock diet possesses an efficiency of unity, the values are 1.85 for sucrose 0.44 for fat and 0.61 for casein.