Amino acid incorporation into total protein and levels of S-100 protein in discrete rat brain areas after prolonged protein or amino acid restriction

Young adult rats were fed an isocaloric diet for 28 days. The diet consisted of either 22% casein, or protein-restricted food consisting of a 5% mixture of soy and whey protein, or a synthetic amino acid mixed diet devoid of the essential amino acids tryptophan, valine, lysine, and threonine. The level of the nervous tissue-specific S-100 protein was quantified immunoelectrophoretically in 9 different brain areas. A marked decrease of S-100 was observed in hippocampus and posterior part of the cerebellar vermis per g wet weight in protein-restricted rats. An additional lowering was noticed in sensory motor cortex per mg soluble protein. This effect was potentiated with the amino acid-deficient diet. The in vitro incorporation of 3H-leucine into cerebellar proteins was slightly decreased in the low-protein-fed rats, and more markedly decreased in those receiving an amino acid-restricted diet.