Nutritional disturbances of
protein metabolism in the liver are reviewed in relation to feeding experimental animals the following diets: a) purified diets deficient in
amino acids; b)
amino acid mixtures or single
amino acids; c)
protein-free (
amino acid-free) diets; or d) hypertonic or
hypotonic solutions. The effects of
tube-feeding the diets or dietary components for days, hours, or minutes on hepatic polyribosomes and
protein synthesis are described.
Force-feeding a purified diet free of single
essential amino acids induces within days morphologic changes resembling those that occur in humans with
kwashiorkor, a world-wide
nutritional deficiency disease in children. In this
kwashiorkor-like model, hepatic
protein synthesis and polyribosomal aggregation are increased. Administration of a complete
amino acid mixture or
tryptophan alone, but no other single
amino acid, produces a rapid stimulation (within minutes) of hepatic
protein synthesis and polyribosomal aggregation in animals that had been fasted, fed, or treated with hepatotoxic agents. A single
tube-feeding of a
protein-free (
amino acid-free) diet induces within hours an increase in hepatic
protein synthesis in fasted animals. Administration of
hypertonic solutions rapidly (within minutes) inhibits, while administration of
hypotonic solutions rapidly increases, hepatic
protein systhesis. These experimental findings are reviewed in terms of how alterations in regulatory controls of hepatic
protein synthesis may be influenced by nutritional disturbances. Such information may be of importance in designing and utilizing nutritional approaches in the
therapy of
liver diseases.