J.K. Loosli

D-Amino Acids as Source of Non-Specific Nitrogen for Growth of Rats

Summary Rats fed a diet containing physiological amounts of essential L-amino acids but lacking non-essential amino acids grew at a slow rate. Growth rate was increased by increasing concentration of all essential amino acids. Feeding a mixture of DL-amino acids in comparable amounts resulted in growth retardation of animals. Growth inhibition produced by the racemic mixture was traced to an isoleucine deficiency resulting from inclusion of DL-isoleucine, which was actually a mixture of all 4 isomers, thus effectively diluting the active isomer. Substitution of L-isoleucine or a mixture of L- and D allo-isoleucine for the racemic compound in the DL mixture entirely overcame inhibition and produced growth comparable to that obtained with L-amino acids. The experiments provide evidence that D-amino acids can be effectively used as source of nitrogen for biosynthesis of non-essential amino acids.

Isomerized fat and serum cholesterol in swine.

Summary Adult sows were fed a purified diet and in alternate 3-week periods were fed the diet either with a low fat or a high fat (40% of calories) content. In the high fat periods hydrogenated fats were compared with natural plant fat mixtures designed to have the same fatty acid composition. The difference in the fats studied was in their content of isomerized fatty acids. Also triolein was compared with trielaidin. The hydrogenated fats gave the same serum cholesterol response as their corresponding natural plant fat mixtures. Trielaidin gave a lower (P<0.05) serum cholesterol response than triolein.

Response of growing rats to diets varying in magnesium, potassium and protein content.

Summary Dietary magnesium, potassium and protein interactions were studied in weanling rats. Growth rate, efficiency of feed utilization, and blood serum magnesium and calcium levels were significantly lower in rats fed a magnesium-deficient diet than in those fed a similar magnesium-adequate diet. A diet containing 4 times as much potassium (8132 mg/kg) increased the serum magnesium level 60% after 28 days (1.0 vs. 1.6 mg%) and 90% after 56 days (0.9 vs 1.7 mg%) indicating an inhibition by potassium of the reduction in serum magnesium associated with consumption of magnesium-deficient diet. Typical gross magnesium deficiency symptoms, including reddened ears and paws and convulsions lasting 1–5 minutes were observed, however, in all groups fed low magnesium diets regardless of potassium level. Diets containing 20% protein produced significantly greater growth rate than those containing 10% in the presence of adequate magnesium but not during magnesium deficiency. No histological lesions associated with treatment occurred even after 56 days on test despite the fact that gross magnesium deficiency symptoms appeared as early as one week on test.

Relation of selenium, vitamin E and other factors to muscular dystrophy in the rabbit.

Summary Rabbits maintained on a torula yeast, Vit. E deficient diet developed a severe and rapidly progressing muscular dystrophy. This condition was not prevented by addition to the diet of 1 ppm selenium or of supplements of dl-alpha tocopheryl acetate alone or in combination. Additions of natural feedstuffs (wheat bran, linseed oil meal or kidney beans) to the semi-purified diet did not fully prevent the condition, although they did lessen the severity of the lesion and increase the average number of days of survival indicating deficiencies other than selenium and Vit. E were involved in the particular experimental diets used. A marked alopecia was observed in all animals fed diets not containing a natural feedstuff.