Response of the Liver to Prolonged Protein Depletion

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Abstract
The influence of prolonged protein deprivation followed by protein repletion in the adult male rat upon liver neutral glycerides and cholesterol was studied. Neutral glyceride and cholesterol concentrations increased for 8 weeks. Thereafter neutral glycerides decreased to normal and cholesterol to below normal after 14 weeks of deficiency. Attempts to alleviate the slightly fatty liver produced in the simple protein deficiency by including 0.3% DL-methionine in the protein-free ration produced a marked increase in these liver lipids. These excessive accumulations also reached a maximum after 8 weeks, followed by a decline towards normal. Reintroduction of protein into the rations at the terminal stages of protein deficiency caused a rebound of neutral glycerides and cholesterol to far above normal levels. The exact pattern of this response, however, was influenced markedly by whether methionine had been included in the ration during development of the protein deficiency. Cystine and methionine produced very fatty livers when added individually to the protein-free ration, whereas valine increased neutral glycerides and cholesterol to some extent. Leucine was quite lipotropic, however, and maintained the concentrations of these liver lipids normal or below. Phenylalanine was also somewhat lipotropic. Other essential amino acids had no effect. Omission of the dietary source of lipids (corn oil) had no effect on the excessive accumulation of neutral glycerides or cholesterol produced by methionine in the protein-free ration.