Plasma Amino Acids and Excretion of Protein End Products by Mice Fed 10 or 40% Soybean Protein Diets with or without Dietary 2-Acetylaminofluorene or N,N-Dinitrosopiperazine

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Abstract
Studies were conducted with 5- to 8-week-old male and female B6C3F1 mice to determine the influence of two carcinogens, 2-acetylaminofluorene (AAF) and N,N-dinitrosopiperazine (DNP), on plasma amino acid concentrations and on the excretion of lipids and nitrogenous metabolites. The carcinogens, AAF and DNP, were fed at concentrations of 0.25 and 0.05 g/kg of purified diet, respectively. Soybean protein constituted either 10 or 40% of the diet. Nutritional balances were measured over a 7-day period, after 7 days of acclimatization. Females ate less feed, gained less weight during acclimatization and excreted less fecal lipid as a percentage of intake than males. On the average, animals fed 40% protein consumed less total feed than those fed 10% protein. During acclimatization, DNP-fed animals ate and gained significantly less than controls. During week 2 DNP-fed animals gained significantly less than controls, although their feed intake was not significantly different. Fecal lipid excretion as a percentage of intake was significantly lower with carcinogens in the diet. The 40% protein diets increased lipid excretion in total and as a percentage of intake. With the exception of decreasing fecal lipid, AAF caused no consistent changes in feed intake, body weight, nitrogen (N) retention or N excretion. Neither carcinogen significantly influenced total fecal or urinary N, or the relative concentrations of the different forms of urinary N, when expressed as a percentage of N intake. Plasma ammonia rose with AAF feeding and plasma histidine rose with DNP feeding. Plasma concentrations of other amino acids were not changed consistently by either carcinogen. Feeding 40% protein caused a significant rise in plasma branched-chain amino acids, glycine and phenylalanine, and a significant decline in aspartate, threonine, serine, proline, citrulline, lysine and arginine.