ABSTRACT
Objective To investigate the effect of chronic iodine excess on hypothalamic type Ⅱ deiodinase (D2) and serum thyrotropin releasing hormone (TRH) levels in rats. Methods One hundred and eighty four-week-old Wistar rats were randomly divided into control group (NI) and 3-fold, 6-fold, 10-fold, and 50-fold high iodine (HI) groups. Double distilled water and iodine solutions at concentrations of 277, 692, 1 245, and 6 788 μg/L were administered for 4, 8, 12, and 24 weeks, respectively. Brain tissue was taken after sacrifice, serum TRH levels were detected by ELISA, and hypothalamic D2 levels were detected by immunohistochemistry. Results Serum TRH levels in the 10-fold and 50-fold HI groups at 4 weeks, 6-fold and 50-fold HI groups at 8 weeks, 6-fold HI group at 12 weeks, and the 3-fold and 50-fold HI groups at 24 weeks were significantly lower than those in the control group (P ＜ 0.05). The results of immunohistochemistry revealed that the expression of hypothalamic D2 at each time-point was increased in the HI groups in comparison with the control group. Conclusion Chronic iodine excess can boost the expression of hypothalamic D2 and lessen the serum TRH level in rats.