Influence of Selected Amino Acid Deficiencies on Somatomedin, Growth and Glycosaminoglycan Metabolism in Weanling Rats

The effects of lysine-, methionine- or histidine-deficient diets compared to a control diet fed ad libitum or 15, 10 or 5 g/d were studied in weanling rats. Feed intake was 5–7 g/d for the amino acid-deficient animals. After 3 wk, all amino acid-deficient rats had lost more weight (P < 0.01) than the controls fed at comparable energy levels. Serum somatomedin (Sm) activity was significantly decreased in lysine- (0.55 U/ml), methionine- (0.32 U/ml) and histidine-deficient (0.38 U/ml) rats compared to rats fed the control diet ad libitum (1.6 U/ml). Differences between amino acid-deficient and calorie-restricted animals were not significant. A similar response was observed in 35SO4 uptake by cartilage glycosaminoglycans (GAG). Caloric restriction and amino acid deficiency each resulted in lower 35SO4 uptake by cartilage GAG than occurred with ad libitum feeding, but there were no significant differences between the rats fed amino acid-deficient diets and those fed 5 or 10 g of the control diet. Compared to rats fed the control diet ad libitum, plasma growth hormone (GH) concentrations were lower in the rats fed 5 or 10 g of control diet per day and in those fed amino acid-deficient diets (P < 0.05), but GH concentrations were not consistent with the growth retardation observed. The results confirm that Sm and GAG activities are reduced in protein-energy restriction independent of GH. However, changes could not be attributed to specific deficiencies of lysine, methionine and/or histidine.