Amino acids and the kidney.

The kidney has an important role in the metabolism of amino acids and control of plasma concentrations. Reabsorption by the tubules recovers about 70g/day of amino acids, derived from both the diet and metabolism in other tissues. Amino acids regulate haemodynamics and proteolysis and maintain integrity of the kidney. Abnormal plasma and muscle amino acid profiles in chronic renal failure (i.e. low essentials and tyrosine with high nonessentials) first indicated malnutrition, which can be partially corrected by supplementation. The loss of effective kidney tissue and uraemia, in addition to nutrition, have been considered in studies of phenylalanine hydroxylation used to investigate low tyrosine. Investigations in normal kidney have shown that glutamine uptake maintains acid-base homeostasis, glycine and citrulline are removed, and serine and arginine are released into the circulation. These metabolic processes are impaired in chronic renal failure. Uraemia affects most tissues and causes malnutrition, whilst acidosis activates catabolism of amino acids and proteins in muscle. Hyperinsulinaemia probably depresses plasma branchedchain amino acids and particularly valine. These abnormalities are less likely to respond to dietary supplementation.