Spontaneous thymic lesions were investigated in Wistar (Cpb:WU) rats. Thymic tumors were not uncommon and most showed medullary differentiation. Thymic involution was investigated in a limited group of animals in which the survival rate for males and females was similar. The histological pattern of thymic involution differed between sexes. Severe thymic involution occurred more frequently in males than in females and at an earlier age.
The objective of this experiment was to compare the effects of diets with either a non-fermentable fibre source (cellulose) or a fermentable fibre source [galacto-oligosaccharide (GOS)], combined with different levels of dietary fat, on the development of colorectal cancer. Male Wistar rats were fed AIN76-based diets with either a low or high level of cellulose, or a low or high level of GOS, for 9 months. The fat content of the diets was low, medium or high. All rats were treated with 1,2-dimethylhydrazine to induce colorectal tumours. Generally, the tumour incidence increased with increasing fat content in the diet. Despite marked faeces bulking, dietary cellulose either had no effect or an enhancing effect on the formation of colorectal tumours in general, although the development of carcinomas was decreased. GOS appeared to be highly protective against the development of colorectal tumours, as was demonstrated by an inhibitory effect on tumour incidence, multiplicity and size, regardless of the fat content of the diet. Neither fibre source influenced the bromodeoxyuridine labelling index determined in colon crypts or tumours. In animals fed high-GOS diets, the caecal content was significantly increased in weight and significantly decreased in pH. It was concluded that tumorigenesis was enhanced by increased fat content of the diet, and that the diets containing fermentable GOS conferred a greater protection against colorectal cancer than did the diets containing non-fermentable cellulose.
The purpose of the present study was to investigate the modulating effect of heat processing and of vegetables and fruit in human diets on 1,2-dimethylhydrazine (DMH)-induced colon tumors. Groups of 36-45 male Wistar rats were fed for the whole experiment, starting at 4 weeks of age, one of the following diets: a semi-synthetic animal diet (A, control); diet A to which vegetables and fruit were added (B); a raw human diet (meat, bread and eggs) supplemented with semi-synthetic compounds (C); diet C with fried or baked products (D); a complete human diet consisting of heated products, and vegetables and fruit (E). The animal diets (A and B) contained 21.6% fat energy (E), 26.0% protein E, 52.4% carbohydrate E and 10.7% (w/w) fiber. The human diets (C, D and E) contained 40.6% fat E, 13.2% protein E, 46.2% carbohydrate E and 5% (w/w) fiber. Starting at 8 weeks of age and after 4 weeks of feeding the experimental diets, each rat was s.c. injected 50 mg/kg body wt, DMH for 10 weeks once weekly. At the end of the experiment, at the age of 9 months, all rats were killed and macroscopic abnormalities were collected. The colon was examined microscopically for tumors and lesions suspected of being tumors. The results revealed a lower incidence of adenomas in rats consuming the animal diet with vegetables and fruit (B) compared with the control animal diet (A). In contrast to the animal diets, vegetables and fruit added to fried or baked human diets showed no protection at all, but even increased the incidence of carcinomas. Heat processing alone had no significant effect on the DMH-induced tumor incidence. As the fat content and heat processing were main variables between the animal and human diets containing vegetables and fruit, the results obtained suggest that one of these factors or both influence the tumor-modulating effect of non-nutrient substances in vegetables and fruit.
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