The Effect of Dietary Protein Depletion and Repletion on Rat Hepatic Mixed Function Oxidase Activities

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Abstract
Male, weanling rats, 24 days of age were fed purified diets containing either 5% casein (LP) or 20% casein (HP) to determine the temporal vulnerability of hepatic microsomal mixed function oxidase (MFO) activity to dietary protein depletion and repletion. LP-induced depression of MFO activity had previously been shown to be partially caused by an inhibition of liver cell proliferation; therefore, measurements of liver size, DNA content, and microsomal protein were made. The LP diet inhibited body weight gain and increased relative liver size. The liver was characterized by 220% more lipid and a 60% increase in cell size for 50 to 75% of the cells (measured histologically). Microsomal protein and DNA contents were compared per g liver, per total tissue, and per total body weight in order to discern their relationships to MFO activities. Microsomal protein, on a body weight basis, is quickly depressed by the LP diet, primarily because of cellular losses, even though there was a compensatory increase in tissue size in these animals. Hyperplastic growth was promptly interrupted by the LP diet. Refeeding the HP diet restored microsomal protein and relative liver size in about 2 to 4 weeks with recovery being more prolonged the longer the deficient period. MFO activities were measured by ethylmorphine (EM) N-demethylase and aniline (AN) hydroxylase. These activities, when expressed on a body weight basis, were quickly depressed by the LP diets regardless of whether rats were started at 24 or 39 days of age. Recovery of each enzyme activity by feeding the HP diet required about 2 to 4 weeks, or, in other words, about the same length of time required to develop the original deficiency. In additional experiments, the high levels of sucrose used in these diets accounted for only a small proportion (6–17%) of the LP-induced depression of MFO activities. An elevation in plasma corticosterone level was observed in the LP rats after 8 and 15 days and a potential relationship with MFO activities is discussed.