ABSTRACT
Objective To explore the effect of iodine excess on bone metabolism in experimental autoimmune thyroiditis (EAT) rats. Methods We selected 36 female Lewis rats with body weight of (131 ± 15)g,and divided them into 3 groups randomly: control group, EAT group and EAT + high iodine group, assuring 12 rats in every group. These rats were fed fodder with different concentration of iodine(0.9,0.9, 18.0 mg/kg), and rats in EAT group and EAT + high iodine group were immunized with pig thyroglobulin(pTG) and complete Freund's adjuvant(CFA) to create EAT model. After two weeks, the pathological changes of the thyroid tissues were observed,and the serum thyroid autoantibody[thyroglobulin antibody(TGAb) and thyroid microsomal antibody(TMAb)], the thyroid hormone levels[triiodo thyronine(T3) and thyrine(T4)] and some relevant data of bone metabolism[bone gla protein (BGP), tartrate-resistant acid phosphatase (TRAP), C-terminal propeptide of type Ⅰ procollagen (PICP),C-terminal telopeptide of type Ⅰ collagen (ICTP), insulin-like growth factor- 1 ( IGF- 1 ), osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL)] were measured. Results Inflammatory cell infiltration and local follicular structural damage were observed in the thyroid tissues of EAT rats in EAT group and EAT + high iodine group, and the pathological changes of EAT + high iodine group were mainly thyroid follicular expansion and integration. The level of serum TGAb, TMAb, T3 and T4 of EAT rats in EAT group and EAT + high iodine group[ (63.01 ± 12.36)%, (60.62 ± 11.24)%, (3.78 ± 1.43), (125.12 ± 16.00)pmol/L and (75.00 ± 15.44)%,(72.15 ± 15.00)%, (3.69 ± 0.91 ), (149.40 ± 20.67)pmol/L] were higher than those of the control group[ (4.47 ±1.04)%, (5.73 ± 1.01 )%, (0.75 ± 0.12), (76.91 ± 9.30)pmol/L, all P ＜ 0.05], and the level of serum TGAb,TMAb and T4 of EAT rats in EAT + high iodine group were higher than those of the EAT group(all P ＜ 0.05).The level of serum BGP, PICP and IGF- 1 in EAT group[ ( 1.70 ± 0.31 ), ( 11.31 ± 1.52) μg/L, (0.31 ± 0.06 ) mg/L]were lower than those of the control group[ (8.60 ± 0.33), (14.28 ± 3.10)μg/L, (1.16 ± 0.02)mg/L, all P ＜0.05], and the level of serum TRAP, ICTP, OPG and RANKL[ ( 19.88 ± 3.60)ng/L, (2.43 ± 0.82), (22.36 ± 2.80),( 1.35 ± 0.23 )μg/L] were higher than those of the control group[ ( 14.57 ± 3.56)ng/L, (0.50 ± 0.20), (1.61 ± 0.34),(0.10 ± 0.02)μg/L, all P ＜ 0.05]; compared with EAT group, the level of PCIP and OPG in EAT + high iodine group [ (8.03 ± 1.84), ( 16.80 ± 3.79)μg/L] were obviously decreased(all P ＜ 0.05). Conclusions The reinforcement of differentiation and maturation of osteoblast in the EAT rats results in the increasing of bone resorption. The activity of osteoblast and osteoclast of the EAT rats are inhibited by excessive iodine, showing a low conversion-type osteoporosis.