EFFECTS OF IODINE DEFICIENCY AND HIGH-FAT DIET ON N-NITROSOMETHYLUREA-INDUCED MAMMARY CANCERS IN RATS

Abstract

The effects of an altered content of dietary I and fat on the development of N-nitrosomethylurea-induced mammary tumors in rats were studied and correlated with thyroid and pituitary function studies. In 3 separate experiments, animals fed a semisynthetic diet containing 11.8% fat had an earlier time of tumor appearance and greater tumor burden than did controls maintained on a diet containing 4.6% fat. These diet-associated changes were markedly inhibited by ovariectomy, indicating that the tumor growth was hormone responsive. The diet with increased fat content may enhance tumor growth through alterations in prolactin metabolism. No consistent elevation in serum prolactin and no increase in pituitary prolactin synthesis in vitro were found. Rats on an I deficient form of the high-fat diet had no greater tumor growth than did animals receiving an I supplemented form of the same diet. I deficiency apparently does not promote mammary tumorigenesis. Ovariectomy led to a highly significant depression of thyroid-stimulating hormone production in vitro. Estrogens may directly influence thyroid-stimulating hormone synthesis in vivo and thus contribute to the sex-related differences in thyroid physiology.