Quality of dietary protein and dietary restriction during promotion on chemically-induced mammary carcinogenesis and serum lipids concentrations in rats




Barner, Claudia Ann

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One hundred and twenty-six Sprague-Dawley female weanling rats were fed AIN-76 diet from 4 to 9 weeks of age. At the age of 8 weeks, six rats were killed for the determination of baseline serum total cholesterol (TC), high density lipoproteincholesterol (HDL-C), and triacylglycerol (TG) concentrations. 7,12- dimethylbenz(a)anthracene (5 mg/1 00 g. b.wt.) was administered intragastrically in 96 rats and sesame oil was similarly administered to 24 control rats. At the age of 9 weeks, 6 OM SA-treated and 6 sesame oil-treated rats were killed and serum lipid concentrations determined. The remaining 90 DMBA-treated and 18 sesame oiltreated rats were randomly assigned to three dietary treatment groups during the promotion phase of carcinogenesis (9-26 weeks of age): casein , ad libitum (CA); casein, 80°/o of CA's intake (CR); wheat gluten, 80°/o of CA's intake (WR). Serum TC, HDL-C, and TG concentrations were determined at two other time periods: 1) when the initial tumor in each of the first 10 rats reached 1-2 em in diameter, and 2) when the rats were 26 weeks of age (the termination of the study). Palpable mammary tumor incidence was 90°/o, 80°/o, and 73.3°/o for CA, CR, and WR, respectively. The number of palpable tumors, non-palpable tumors, and multiple tumors were not significantly different among the three groups. Tumors developed significantly (p<0.05) earlier and weighed significantly more in the CA group (9.2 wk; 10.1 g) than in the CR (11.1 wk; 2.9 g) and WR groups (11.4 wk; 1.6 g). Although the 20°/o caloric restriction did not produce significant differences in tumorigenesis between the dietary groups, the adlibitum fed rats had a greater number of mammary tumors. These data indicate that the caloric restriction had a greater influence than the quality of dietary protein in depressing tumorigenesis in rats. The DMBA-induced tumor growth had no significant effect on serum TC, HDL-C, and TG concentrations. When the tumor size was 1-2 em, the serum TC in the WR group of rats was 1. 79 mmoi/L, significantly less than CA group treated with DMBA (2.87 mmoi/L). At the termination of the study, WR rats had significantly lower TG (56.07 mg/dl) compared to the CA animals (1 01.08 mg/dl). The HDL-C concentrations in all 3 dietary groups remained similar throughout the course of the study. These data suggest that while dietary restriction contributed to the reduced concentrations of TC or TG, neither the type nor the advancement of tumor development had an effect on serum lipids.



Low-protein diet, Proteins in animal nutrition, Carcinogenesis in animals