[Promoting effect of endogenous TSH on carcinogenesis of rat thyroid transplanted into the spleen]

In an attempt to clarify a modifying effect of TSH on thyroid tumorigenesis, we carried out intrasplenic thyroid autotransplantation in rats treated with a thyroid carcinogen, diisopropanolnitrosamine (DIPN). Experiments comprised 3 groups of Wistar male rats: Group I (effective no., 15), total thyroidectomy plus hemithyroid transplantation 2 weeks after subcutaneous injection of DIPN at a dose of 2.4g/kg BW; group II (effective no., 22), DIPN alone; group III (effective no., 18), transplantation alone. The thyroid lesions of all rats at week 28 were examined by histopathology and enzyme histochemistry for gamma-glutamyl transpeptidase (GGT). Periodical radioimmunoassay for serum T3, T4 and TSH revealed low levels of T3 & T4 for at least 10 weeks and increased level of TSH until week 18 after the transplantation. Altered foci (AF) occurred in 36% and 6% of rats in group I and group II, respectively, whereas neoplastic nodules (NN) were found in 53% of rats only in group I. Both AF and NN displayed a positive reaction for GGT which was considered to be a useful marker for preneoplastic and neoplastic thyroid lesions. The present data are indicative that increased serum level of TSH for a significant period may exert a promoting effect on thyroid tumorigenesis.