Growth, free plasma and muscle amino-acids in uraemic rats fed various low-protein diets.

The nutritional effects of low-protein diets are difficult to assess in humans. Normal and uraemic growing rats were therefore fed: a moderately low-protein (12%) reference diet (diet R), two 5% casein diets, one supplemented with essential amino acids (AA) (diet A) and the other with their keto acids (diet K), and a 7% casein diet isonitrogenous with diet K (diet L). Appetite and growth of both uraemic and control rats were identical on diets R and A and were reduced on diets K and L. Stunting was prominent in rats fed diet L and more severe than in those on diet K. Diet K induced marked anorexia in controls. This effect was smaller in uraemic rats, which were all anorectic, regardless of the diet. Plasma essential AA were similar in rats on diets R and A but low in control rats fed diets L and K. In particular, diet K did not improve the branched-chain AA levels although it produced better growth than diet L. Plasma and muscle threonine were surprisingly elevated in rats on the semi-synthetic diets A and K, despite identical or lower consumptions. Regardless of the diet, uraemia resulted in unchanged or increased plasma essential AA, despite reduced appetite and stunting. Uraemia caused a marked rise in some non-essential AA. Muscle essential AA, except for threonine, were essentially unaltered and did not correlate with growth or uraemia.