A study of the efficacy of L-3,5-diiodotyrosine and inorganic iodine in iodine-deficiency Wistar rats

Abstract

Objective To study the efficacy of L-3,5-diiodotyrosine (DIT) and inorganic iodine (KIO3) in iodine-deficiency Wistar rats. Methods Sixty Wistar rats, weighting about 160-180 g, were divided into two groups according to body weight by the random number table method: iodine-deficiency model (40 rats) was fed with low-iodine food (the iodine content was 35.9 μg/kg); optimal-iodine model (20 rats) was fed with low-iodine food and given with KIO3 water (the iodine content was 18 mg/L) 0.5 ml by intragastric once a day. Model was established for 3 months. Iodine-deficiency model was subdivided into low iodine (LI) group, KIO3 group and DIT group, eight, nine, ten rats in each group; from optimal-iodine model, nine rats were randomly selected as optimal iodine (NI) group. LI group was fed with low-iodine food; KIO3 group was fed with low-iodine food and given with KIO3 water (the iodine content was 18 mg/L) 0.5 ml by intragastric once a day; DIT group was fed with low-iodine food and given with DIT water (the iodine content was 18 mg/L) 0.5 ml by intragastric once a day; NI group was fed with low-iodine food and given with KIO3 water (the iodine content was 18 mg/L) 0.5 ml by intragastric once a day. After 3 months, 24-hour urine of the rats was collected. According to the method for determination of iodine in urine by As3 +-Ce4+ catalytic spectrophotometry (WS/T 107-2006), iodine content in urine was detected. Rats were anesthetized intraperitoneally with 25% urethane, blood from abdominal aortic was collected to determinate the serum thyroid hormone [total triiodothyronine(TT3), total thyroxine (TT4), free triiodothyronine (FT3), free thyroxine (FT4)] level in rats by automatic electrochemical luminescence immunoassay. All the rats were sacrificed to analyze the thyroid weight. Results ①The urine iodine showed significant differences in the four groups (χ2 = 25.24,P < 0.05). The median of urine iodine concentration in the LI, NI, KIO3 and DIT groups were 3.00, 286.14, 223.37, 214.33 μg/L, respectively. The urine iodine concentration in LI group was significantly lower than those of other three groups (all P < 0.05). ②The serum TT3, TT4, FT3, FT4 levels showed significant differences in the four groups (F = 63.48, 140.73, 130.20, 365.27, all P < 0.05). And the hormone levels in KIO3 group were lower than those of the DIT group [TT3: (1.57 ± 0.20) vs. (1.97 ± 0.18) mmol/L, TT4: (51.23 ± 4.90) vs. (71.94 ± 5.27) mmol/L, FT3: (5.34 ± 0.45) vs. (6.98 ± 0.33) pmol/L, FT4: (26.18 ± 2.30) vs. (35.47 ± 2.28) pmol/L, all P < 0.05]. ③The color of thyroid in KIO3 and DIT groups became pale pink. The absolute and relative thyroid weight showed significant differences in the four groups (F = 225.05, 345.40, all P < 0.05). The absolute thyroid weight [(31.76 ± 1.75) mg] and relative thyroid weight [(11.69 ± 3.47) mg/100 g] in DIT group was lower than that of the KIO3 group [(36.31 ± 5.23) mg, (12.83 ± 4.38) mg/100 g, all P < 0.05]. Conclusion Animal experimental results show that DIT has a better iodine-supplementing efficacy than that of KIO3. Key words: Iodine; L-3,5-diiodotyrosine; KIO3; Rats