Effect of 17 β-estradiol, Retinoic Acid and Tamoxifen upon Primary and Transplanted Thyroid Tumor in B5C3F1 Mice Fed an Iodine Deficient Diet

This study was aimed to establish TSH dependent, transplantable thyroid tumor (TT) in B6C3F1 (BCF1) mice. In addition, transplanted TT was examined for its growth in mice given 17β- estradiol (E2), retinoic acid (RA), tamoxifen (TAM), T3 and T4. Both sexes of BCF1 mice were observed for 12 months under IDD and distilled water (DW), starting at 4 weeks of age. Groups of mice received an i.p. injection of radioactive iodine (131I) once at a dose of 60 μ Ci/head and/or given 0.25 mg E2 pellet s.c. One piece of induced pituitary or thyroid tumor was individually dissected aseptically and s.c. grafted under the fat pad of one site of the neck in the same strain of mice at 5 weeks of age. All mice were sacrificed between 7.5 to 13.5 months after grafting the tumors depending on the experiments. The transplantability of both pituitary and thyroid tumor was 100% in IDD mice, but TT was about 50% with a combined treatment of IDD plus E2. A supplement of thyroid hormones of T3 or T4 in mice with IDD completely inhibited the growth of in situ or grafted thyroid tumors. The growth of in situ thyroid gland was significantly promoted by the oral administration of RA in both sexes, whereas the growth of transplanted TT was significantly increased by RA in the female, but not in the male. Oral administration of TAM proved inhibitory upon in in situ and transplanted TT in the male, but not in the female. Thyroid tumor induced by IDD could grow only in mice with IDD and was partially regulated of its growth by RA and TAM.