Effect of 4,4′-Oxydianiline on the Thyroid and Pituitary Glands of F344 Rats: A Morphologic Study With the Use of the Immunoperoxidase Method

F344 rats of both sexes were fed one of three concentrations (0.02, 0.04, 0.05%) of 4,4′-oxydianiline (CAS: 101-80-4), an intermediate in the manufacture of polyimide resins, mixed in the diet for 2 years. The incidence of hepatocellular neoplasms was increased in all the 3 groups of male rats and in female rats of the middle- and high-dose groups. The incidence of hyperplastic and neoplastic changes in the follicular cells of the thyroid gland was increased in male and female rats of the middle- and high-dose groups. The population of thyrotrophs (thyrotropin-producing cells) was increased in the pituitary glands of rats with neoplasms of the thyroid gland. These cells were distinct from prolactin cells. The increase in the number of thyrotrophs suggested insufficient hormone production by the induced thyroid tumors.