Effect of neonatal malnutrition on leucine renewal and protein biosynthesis in neurons of rats.

Starting 1--3 days before delivery, pregnant rats were fed isocaloric diets containing either a low (5% casein) or a normal (20% casein) level of protein. At 14 days of age, the malnourished pups showed lower body, brain, and forebrain weights. The number of cells in the forebrain was lower and their size was smaller in the malnourished group. In order to study the turnover rate of 14C-leucine in the free amino acid pool and the rate of 14C-leucine incorporation into TCA-precipitable protein in neuronal cell bodies, a neuronal enriched fraction (NEF) was prepared. Malnutrition altered the free amino acid pool of the NEF by increasing the content of lysine+ornithine, glycine, and aspartic and glutamic acids and lowering that of histidine and threonine. The pools of the remaining amino acids were not altered. The turnover rate of free 14C-luecine was reduced to 60% of that of the controls. The rate of 14C-leucine incorporation into TCA-precipitable protein, corrected for its turnover rate in the free pool, was reduced to 64% of that of the controls.