The effect of differences in level of dietary
selenium on the induction of esophageal and
bladder tumors in rats by two
nitrosamines was investigated. Groups of 20 female F344 rats were given a synthetic diet containing less than 0.05 ppm Se to which
selenium (as
sodium selenite) was added at the concentration of 0.35, 0.7, 1.4 and 2.1 ppm
selenium. These four groups, plus one without added Se, were treated with 20 ml per rat per day, 5 days a week, of a
solution of
nitrosomethylcyclohexylamine containing 5 mg/liter. A parallel five groups were treated in the same way with a
solution of
nitrosomethyl-3-carboxypropylamine in
drinking water containing 600 mg per liter, as
drinking water. Treatment lasted 28 weeks, at which time some animals had developed
tumors. A group of 20 rats fed 0, 1.4 and 2.1 ppm Se was not treated with
carcinogen. Rats consuming 1.4 ppm or 2.1 ppm Se gained weight more slowly than other groups. There was no significant difference in survival between the five groups treated with each
carcinogen but receiving different dietary levels of
selenium. Neither was there any significant difference between groups receiving each
carcinogen in the incidence of
tumors of the esophagus induced by
nitrosomethylcyclohexylamine or of
tumors of the urinary bladder induced by nitrosomethylcarboxypropylamine. Control rats on the synthetic diets did not survive as well as untreated rats eating regular chow diet. In these conditions there was no effect of dietary
selenium levels on the induction of
tumors in female rats by the two carcinogenic
nitrosamines we used.