Induction of thyroid neoplasms in the rat. A histochemical, immunohistochemical, autoradiographic and ultrastructural study.

Papillary carcinomas of the thyroid gland induced in rats by combined methylthiouracil (MTU)/nitrosomethylurea treatment were studied electron microscopically and histochemically for their acid phosphatase activity, radioactive iodine uptake and for their thyroglobulin synthesis. The papillary carcinomas accumulated radioactive iodine, synthesized thyroglobulin and showed a perinuclear localization of acid phosphatase activity in the cytoplasm. After omitting the reactive thyrotropic effect (cessation of MTU administration) a decrease of both iodine organification and acid phosphatase activity was observed. The synthesis of thyroglobulin was also reduced. The changes in the ultrastructure of tumour cells corresponded to the respective functional activities. The results suggest that the papillary carcinomas may have a functional dependence on thyroid-stimulating hormone.