The influence of diet and dimethylhydrazine on the small and large intestine of vervet monkeys.

The morphological features of the intestine in monkeys on various diets with and without carcinogen were studied. Seventy adult female vervet monkeys were divided into seven treatment groups. Four groups received a Western high-fat low fibre diet (WD); two a Prudent low-fat higher fibre diet (PD) and one a control low-fat high fibre diet (CD). Three groups (2 WD, I PD) received dimethylhydrazine 10 mg/kg intramuscularly at 14 days intervals. After 18 months, monkeys of two groups on the WD were transferred to the PD and 30 months later all were terminated. Small and large intestine were examined macroscopically, histologically with morphometry, histochemically for acid and neutral, sialo- and sulphomucins and enzyme-histochemically for mucosal gamma-glutamyltranspeptidase (GGT) activity. Large intestines in all other than CD, particularly in WD-treated animals were dilated, thin walled, less corrugated and contained more residual contents. Diverticulosis was found to be mostly associated with WD. Apparently histologically normal colonic mucosa showed changed mucin secretion, predominantly in WD groups, and also GGT activity in all but CD groups. Changes which could be associated with pre-malignancy occurred predominantly but not exclusively in carcinogen treated animals. Within 4 years of feeding to monkeys, diets used by affluent western man caused distinct changes suggestive of the development of intestinal diseases such as megacolon, diverticulosis and cancer. Feeding a prudent diet resulted in only a mild reduction of these signs, whereas they were absent in a usual monkey diet that was much lower in animal products and refined carbohydrates.