Effect of long-term amino-acid deficiency on the amino-acid composition of the body
The aim of this study was to assess changes in the amino-acid composition of the body and in the fractional protein synthesis rates of individual organs or of haemoglobin as a result of long-term amino-acid deficiency in both growing and adult animals. The body weight loss of adults and the growth rates of growing animals were controlled by adjusting the degree of amino-acid deficiency according to individual body weight changes. Adult rats given amino acid-deficient diets had lower absolute weights of muscle (p = 0.052), liver (p = 0.002) and gastrointestinal tract (p < 0.001) than adequately-fed animals but chronic marginal amino-acid deficiency did not result in any measurable effect on whole-body amino-acid composition in comparison with well-nourished rats. In growing rats, liver weight, liver protein mass, fractional (% per day) and absolute (g / liver per day) synthesis rates of total liver protein, liver RNA activity and absolute albumin synthesis rate (g / liver per day) were depressed by long-term dietary deficiency of leucine, isoleucine or histidine. There were no significant differences in liver RNA capacities or relative albumin synthesis rates, however, between the adequate and the deficient groups. In growing pigs, deficiency of isoleucine, histidine or tryptophan depressed growth rate and the weights of liver, gastrointestinal tract, and muscle (biceps femoris). The fractional rates of total protein synthesis, both in individual tissues (muscle, skin and liver) and of haemoglobin, were also reduced. Pigs given histidine- or tryptophan- deficient diets had higher body hydroxyproline concentrations, suggesting changes in the deposition of collagen relative to other body proteins. The histidine-deficient pigs had lower whole-body histidine concentrations, due to absolute decreases in both haemoglobin and in free peptides rich in histidine. The histidine-deficient pigs also had low histidine concentrations in skin.