Studies on the carcinogenicity of potassium iodide in F344 rats

A chronic toxicity and carcinogenicity study, in which male and female F344 /DuCrj rats were given potassium iodide (KI) in the drinking water at conce ntrations of 0, 10, 100 or 1000 ppm for 104 weeks, and a two-stage carcinog enicity study of application at 0 or 1000 ppm for 83 weeks following a sing le injection of N-bis(2-hydroxypropyl)nitrosamine (DHPN), were conducted. I n the former, squamous cell carcinomas were induced in the salivary glands of the 1000 ppm group, but no tumors were observed in the thyroid. In the t wo-stage carcinogenicity study, thyroidal weights and the incidence of thyr oid tumors derived from the follicular epithelium were significantly increa sed in the DHPN+KI as compared with the DHPN alone group. The results of ou r studies suggest that excess KI has a thyroid tumor-promoting effect, but KI per se does not induce thyroid tumors in rats. In the salivary gland, KI was suggested to have carcinogenic potential via an epigenetic mechanism, only active at a high dose. (C) 2000 Elsevier Science Ltd. AN rights reserv ed.