Effects of the irreversible ornithine decarboxylase inhibitor, alpha-difluoromethylornithine, aflatoxin B1, and choline deficiency on hepatocarcinogenesis.

Liver carcinogenesis was induced in rats by aflatoxin B1 (AFB1) enhanced by a choline-deficient diet. In Experiment 1, the ornithine decarboxylase inhibitor, alpha-difluoromethylornithine (DFMO), was administered by gavage to one group only during AFB1 administration; another group received DFMO during AFB1 administration and for 2 months after carcinogen administration. These two groups were compared to two control groups, one given AFB1 and fed the choline-deficient diet and another fed the deficient diet only. In a second experiment, DFMO was administered at a concentration of 2% in the water for 3 weeks and then at 1% for the remainder of the study. Rats from each group in Experiment 1 were killed at 2, 8, and 10 months after AFB1 administration and the development of tumors was followed by histology; autoradiography of [3H]thymidine incorporation into DNA; enzyme histochemistry; and alpha-fetoprotein determination. The group given DFMO during AFB1 administration was not significantly different from the AFB1-treated control group at 2 and 8 months after AFB1 administration. However, at 10 months following AFB1 and DFMO administration, the [3H]thymidine-labeling index and glucose-6-phosphatase staining were significantly increased. This group had three animals bearing hepatocellular carcinomas as compared to none in the controls. The group given DFMO for 2 months after AFB1 administration had a significantly depressed growth rate 2 months later, but this difference was not apparent after 8 months. After 10 months, there was a significantly increased [3H] thymidine-labeling index and increased volume fraction of gamma-glutamyltranspeptidase in the AFB1-DFMO-treated group as compared to the controls. DFMO appeared to inhibit growth under some conditions, but if administration was discontinued after AFB1 exposure, it appeared to enhance tumorigenesis. In Experiment 2, where a larger dose of AFB1 was used and DFMO was administered in the water from start to finish of the experiment, DFMO inhibited tumor induction and depressed the appearance of markers examined during carcinogenesis. These data indicate that the regimen used for DFMO administration can markedly affect tumor induction.

Lack of effect of dietary fat on N-nitrosomethyl urea (NMU)-induced colon tumorigenesis in rats.

The effect of alterations in the quality and quantity of dietary fat on N-nitrosomethyl urea (NMU)-induced colon cancer in rats was studied. Weanling Sprague-Dawley rats were fed semipurified diets containing 24% beef fat, 24% corn oil, 24% Crisco or the three fats in equal parts to make a total of 5% fat. Macronutrients and micronutrients were adjusted to balance the nutrient to calorie ratios. After 4 weeks of dietary treatment, all rats, except vehicle-treated animals received NMU (1.5 mg) via intrarectal instillation, twice a week for 2 weeks. The animals continued receiving the experimental diets until intestinal tumors developed and surviving animals were sacrificed at 43 weeks. There was no effect of any of the high fat diets tested on intestinal tumor incidence, latency, distribution or size. Cumulative probability of death with colon carcinoma did not differ significantly among the dietary groups.

The effect of butylated hydroxytoluene (BHT) on the rat thyroid.

Butylated hydroxytoluene (BHT) was given to rats in the diet at levels of 500 and 5000 ppm for different periods of time up to 90 days. Iodine uptake by the thyroids, the half life of thyroxine and the weights of liver and thyroid were determined when 5000 ppm BHT was given in commercial or semisynthetic diets containing different amounts of iodine. Iodine uptake was significantly increased in those animals given BHT into the diet, but the half-life of thyroxine was unchanged or slightly prolonged. Thyroid weight was enhanced at both 500 and 5000 ppm BHT, while liver weight was increased ony in the latter. No explanation of the pathogenesis of the effect can be suggested.

Magnesium stearate given perorally to rats. A short term study.

Magnesium stearate was fed to groups of 20 male and 20 female rats at levels of 0, 5, 10 and 20% in a semisynthetic diet for 3 months. Decreased weight gain was found in males in the 20% group. Urolithiasis was found in 8 males and in 7 females in the same group. Reduced relative liver weight was seen in males in the 10% and in the 20% groups, and an increased amount of iron was found in the livers of the 20% group. Nephrocalcinosis was reduced in females in the 20% group. In this experiment the no-effect-level is estimated to be 5% magnesium stearate in the diet, corresponding to 2500 mg/kg body wt/day.

Polycystic changes in rat kidney induced by biphenyl fed in different diets.

Groups of rats were fed biphenyl at various dose levels in a semisynthetic diet and in a commercial chow. The effect levels for induction of polycystic kidney lesions were established by means of urinalysis, organ weight changes, light and electron microscopy, and enzyme histochemistry. The no-effect level, was less than 50 mg/kg bw./day and 300 mg/kg bw./day, when feeding the semisynthetic diet and the commercial chow respectively. This difference in effect level due to the diet is an indication that the diet is of great influence on the results of toxicological experiments.

A short term peroral study of the food colour, Ponceau 6R in pigs.

Ponceau 6R (the tetrasodium salt of 1-(4-sulpho-1-naphthyl-azo)-2-naphthol-3,6,8-trisulphonic acid) was fed to pigs at dietary levels of 0 (control), 100, 500 and 1500 mg/kg body wt./day for 102--105 days. In the 1500-mg group a decrease in weight gain and food utilization was seen, and 1 pig died with a hemolytic anaemia. Dose dependent discolouration was seen of the connective tissue in the groups given 1500 and 500 mg/kg body wt. For this effect the no-effect-level was 100 mg Ponceau 6R/kg body wt. per day.