Serum lipid concentrations during DMBA-induced mammary carcinogenesis of rats fed diets of different types of protein with 20% dietary restriction
One hundred and thirty female Sprague-Dawley weanling rats were given free access of AIN-76 diet until9 weeks of age. At 8 weeks of age, 10 rats were used to determine concentrations of total cholesterol (TC), high density lipoprotein cholesterol (HDL-C) and triacylglycerol (TG). Half of the remaining 120 rats received 7,12- dimethylbenz(a)anthracene (DMBA) and the other half received sesame oil alone. Fifty DMBA- and 50 sesame oil-treated rats were randomly assigned to one ad libitum group, casein diet (C-AL) and four 20% dietary restricted groups fed soy protein isolate diet, (SPI-R), defatted cottonseed flour diet (CS-R), wheat gluten diet (W-R), and casein diet (C-R). Serum TC, HDL-C, and TG concentrations were also determined at one week post DMBA and sesame oil treatment and at the time when the first tumor from each rat grew to 1-2 em in diameter, along with their counterpart in the sesame oil-treated group. The C-AL group exhibited shorter latent period and higher incidence for rats bearing first palpable tumor > 1 em. The SPI-R rats developed the least number of multiple tumors. All the tumors with the size of 1-2 em in diameter except one were mammary adenocarcinomas. No consistent changes in the concentrations of the serum TC, HDL-C, and TG during the development of mammary adenocarcinomas. The concentration of serum TC in the SPI-R rats bearing tumors was significantly higher than those received sesame oil. All groups of rats except the W-R group bearing mammary adenocarcinomas had elevated TG concentrations in comparison to the baseline values. In conclusion, serum TC, HDL-C, and TG concentrations are not directly affected by the development of DMBA-induced adenocarcinomas. Feeding a diet containing plant protein to rats or subjected the rats to 20% dietary restriction could influence the concentrations of serum lipids as well as the outcome of tumorigenesis. The changes occurred in the serum lipids were independent to the development of the tumors.