Abstract: Objective To observe the effects of selenium yeast and vitamin D on related hormones and antibodies in
experimental autoimmune thyroiditis (EAT) rats. Methods Of the 55 female SD rats, 45 were sensitized with porcine
thyroglobulin (pTG) + drinking high iodine water to establish the EAT rat model. The successfully modeled rats (n=40) were
randomly divided into the model group, the selenium yeast group, the vitamin D group and the combined group. There were
10 rats for each group. The remaining 10 rats were used as the control group. Four weeks after boosting the immunity, the
selenium yeast group was administered intragastrically selenium yeast solution + intraperitoneal injection of normal saline,
vitamin D group was intragastrically administered normal saline + intraperitoneal injection of vitamin D3, the combined group
was intragastrically administered selenium yeast solution + intraperitoneal injection of vitamin D3, and the control group and
model group were intragastrically administered normal saline + intraperitoneal injection of normal saline. After 6 weeks, the
serum free triiodothyronine (FT3), free thyroxine (FT4), thyroid stimulating hormone (TSH), thyroglobulin antibody (TGAb),
thyroid peroxidase autoantibody (TPOAb), interferon-γ (IFN-γ), interleukin (IL)-4 and IFN-γ/IL-4 were compared between
five groups. HE staining was used to compare the pathological changes of thyroid tissues in each group. The relative
expression levels of p38MAPK, cyclooxygenase-2 (COX-2) mRNA and relative expression levels of p38MAPK, pp38MAPK, and COX-2 proteins in thyroid tissues were compared between five groups. Results The results of HE staining
showed that the thyroid follicles had normal morphology in the control group. The thyroid follicle structure was damaged,
lymphocyte infiltration and interstitial fibrosis in the model group. There was some improvement in selenium yeast group,
vitamin D group and combined group than those of model group, and the improvement was the most obvious in the combined
group. Compared with the model group, the serum levels of FT3, FT4, TSH, TGAb, TPOAb, IFN-γ, IFN-γ/IL-4, the relative
expression levels of p38MAPK, COX-2 mRNA and the relative expression levels of p-p38MAPK, COX-2 proteins in thyroid
tissues were significantly decreased in selenium yeast group, vitamin D group and combined group (P＜0.05), and the serum
IL-4 level was increased in selenium yeast group, vitamin D group and combined group (P＜0.05). Compared with selenium
yeast group and vitamin D group, the serum levels of FT3, FT4, TSH, TGAb, TPOAb, IFN-γ, IFN-γ/IL-4, and the relative
expression levels of p38MAPK, COX-2 mRNA and the relative expression levels of p-p38MAPK, COX-2 proteins in thyroid
tissues were significantly decreased, and the serum level of IL-4 increased in the combined group (P＜0.05). Conclusion
Selenium yeast combined with vitamin D can effectively inhibit thyroid tissue damage and protect thyroid tissue in EAT rats,
which may be related with the regulatory role by inhibiting the MAPK signaling pathway.

Key words: thyroiditis, autoimmune, vitamin D, rats, Sprague-Dawley, thyroid hormones, Th1-Th2 balance, p38 mitogen-activated protein kinases, selenium yeast