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Influence of Selected Amino Acid Deficiencies on Somatomedin, Growth and Glycosaminoglycan Metabolism in Weanling Rats¹

^* Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR 72205 Department of Foods and Nutrition, Kansas State University, Manhattan, KS 66506

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.

KEY WORDS: • amino acids • somatomedin • glycosaminoglycans

¹ Supported by U.S. Department of Agriculture Grant 5901-0401-9-0325-0, U.S. Public Health Service Grant AM 31420, and contribution No. 85-128-J from the Kansas Agricultural Experiment Station.

Manuscript received 19 October 1984. Revision accepted 26 February 1985.