Response of the Liver to Prolonged Protein Depletion

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Abstract
A study of changes in nitrogen and deoxyribonucleic acid (DNA) content of rat liver cells associated with prolonged dietary protein deprivation followed by repletion has been presented. Pair-fed and ad libitum-fed controls were included throughout. The following conclusions were reached. (1) The number of cells per unit weight of liver as measured by DNA concentration increased to 1.5 to 1.8 times normal during protein deficiency. The pair-fed controls showed the same increase. (2) The amount of nitrogen per cell of the protein deficient group dropped to 68 to 74% of that of the pair-fed controls. The nitrogen per cell of the pair-fed controls fell to 68 to 84% of the normal ad libitum controls. (3) These changes began to show up by 10 days although the maxima were not reached until at least 30 days and in some cases until the animals became almost moribund at 72 days. (4) The ratio of liver weight to body weight increased markedly in the protein deficient rats, whereas in the pair-fed controls it remained about the same as in the ad libitum-fed controls. (5) Although protein repletion returned the total calculated number of liver cells to the same level as that of the ad libitum-fed controls within two days, the state of the liver cells with respect to nitrogen content per cell and number of cells per unit weight of liver was the same as after 30 days of protein deficiency. Body weight did not return to normal until 48 days after repletion was begun. (6) After 48 days of repletion, nitrogen per milligram of liver, nitrogen per cell, and number of cells per milligram of liver of the protein-deficient group and the pair-fed controls returned to normal. However, liver weight per 100 gm of rat and total calculated number of cells per liver were significantly higher than those of the pair-fed controls after 48 days of repletion.