Hepatic transaminase in protein-restricted rats: development of a controlled model

A marginal protein malnutrition model which makes allowances for the increasing nutritional requirements of the growing rat and the effects of dietary manipulation on diurnal rhythms, while still rigidly controlling the level of protein restriction, is reported. A predetermined, constantly increasing intake of four purified diets, providing approximately 40 to 160% of the National Research Council protein requirement for rats was fed to rats receiving a nitrogen-free energy source adlibitum. This standardization reduced within-group variation and allowed precise growth reproducibility. Biochemical parameters were measured at evenly spaced intervals throughout the day to remove diurnal differences from between-group comparisons. Growth, nitrogen balance, and 24-hour means of liver weight, DNA, RNA, protein, and glutamate-oxaloacetate and glutamate-pyruvate transaminases reflected protein intake. However, when growth was depressed 10, 30, or 60%, liver GPT/DNA was depressed 40, 49, or 67%, respectively. Hepatic GPT appears to be a sensitive and accurate indicator of marginal protein malnutrition.