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Effects of High Fluoride and Low Iodine on Thyroid Function in Offspring Rats
Journal of Integrative Agriculture
March 2013
2013, 12(3): 502-508
RESEARCH ARTICLE
Effects of High Fluoride and Low Iodine on Thyroid Function in Offspring Rats GE Ya-ming1, 2*, NING Hong-mei1, 2*, GU Xin-li3, YIN Mei1, YANG Xue-feng1, QI Yong-hua1 and WANG Jundong2 College of Animal Science, Henan Institute of Science and Technology, Xinxiang 453003, P.R.China Shanxi Key Laboratory of Ecological Animal Science and Environmental Medicine, Shanxi Agricultural University, Taigu 030801, P.R.China 3 College of Animal Science and Technology, Shihezi University, Shihezi 832000, P.R.China 1 2
Abstract Thirty-two Wistar rats were divided randomly into four groups of eight with six females and two males in each group. The rats were exposed to high fluoride drinking water (45 mg F- L-1 from 100 mg NaF L-1), low dietary iodine (0.0855 mg kg-1), or both together in order to assess the effects of these three regimens on the thyroid function of the offspring rats. After the animal model was established, the offspring rats were bred and 10-, 20-, 30-, 60-, and 90-d-old rats were used for the experiment. The treatments for the offspring rats were the same as those of their parents. In comparison with control rats, the relative thyroid glands were changed by three regimens, but the mean values of thyroid weight in the experimental groups saw no marked difference. Serum TT3 levels were increased in all stages in the low iodine (LI) group. In the high fluoride (HiF) group, increase in TT3 levels was observed except in 20-d-old rats. Decrease in TT3 at 20- and 90-d and increase in TT3 at 30- and 60-d were found in HiF+LI group. Serum TT4 levels first saw an increase, and then dropped in the LI and HiF+LI group. However, an increase in TT4 was found in the HiF group. The levels of TSH in serum rocketed at d 20, and then dropped in the next stages in experimental groups. The results suggested that thyroid disorder could be induced by high flroride in drinking water, low iodine diet, or both of them. Exposure time to fluoride or low iodine diet was one of the important factors that fluoride can induce the development of thyroid dyfunction. Key words: high fluoride, iodine deficiency, offspring rats, thyroid function
INTRODUCTION Fluorosis is one of the most frequently occurring endemic diseases. Their main clinical statuses were dental and skeletal fluorosis. In recent years, epidemiological investigations have revealed that fluorosis and iodine deficiency have co-existed in developing countries, such as China (Lin et al. 1991; Hong et al. 2001), and India (Susheela et al. 2005). The incidence Received 21 October, 2011
rates of hypothyroidism goiter and cretinism in areas of both high fluoride (HiF) and low iodine (LI) were higher than those in low fluoride areas (Lin et al. 1991; Hong et al. 2001). Fluoride can not only induce damage of hard tissue in the body, but also injure soft tissue in the body. As early as in 1936, several cases of endemic goitre in European women on farms in the districts of South Africa were reported. But that area was known to be iodine-rich, and that area is a known endemic fluorine area. So this halogen (fluoride) was im-
Accepted 23 March, 2012
GE Ya-ming, E-mail: [email protected]; Correspondence WANG Jun-dong, E-mail: [email protected] * These authors contributed equally to this study. © 2013, CAAS. All rights reserved. Published by Elsevier Ltd. doi:10.1016/S2095-3119(13)60251-8
Effects of High Fluoride and Low Iodine on Thyroid Function in Offspring Rats
mediately suspected and considered as one of the main factors inducing goiter prevalence in that area (Steyn et al. 1955). Excess fluoride can accumulate in the thyroid gland, affecte iodine metabolism of thyroid follicle cells, disturb synthesis and secretion of thyroid hormone, and then induce incidence of goiter. But time is an important factor for fluoride damage to the thyroid gland (Liu 2002; Kang and Liu 2002). On the basis of our conducted studies on the brains of young offspring rats when exposed to HiF, LI, or both regimens together in the early stages of development (Wang et al. 2004a, b; Ge et al. 2005a, b, c, 2006), we assessed the effects of HiF, LI, and their combination on thyroid function in offspring rats in the present study.
RESULTS The development of the thyroid gland in offspring rats The ratio of thyroid weight to body weight in offspring rats in controls and experimental groups are shown in Table 1. Compared to the control group, the thyroid gland in low iodine groups (LI) were no change at day 10, were swelled at d 20 and 30, and then thyroid gland began to shrink at d 60 and 90. The trend in HiF and HiF+LI groups showed that the thyroid gland was atrophic at first, swelled and then atrophied from d 10 to 90. But the mean values of thyroid weight in experimental groups had no marked difference.
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Thyroid hormone levels in serum The levels of TT3, TT4 and TSH in serum from the offspring rats according to their treatments are listed in Tables 2-4, respectively. Compared to the control group, the serum TT3 levels in Table 2 show a significant decrease at d 20 in the LI and HiF groups (P<0.05), generally increase at d 30 and 60 in three experimental groups, especially in HiF group (P<0.05). Serum TT4 levels in Table 3 show a generally increase at d 20 and 30 in experimental groups, especially at d 30 (P<0.01). And serum TSH data in Table 4 shows a generally increase only at d 20, decrease at d 30, 60 and 90 in experimental groups. Fig. shows the correlation between TT3 and TT4 in serum induced by high fluoride and low iodine (correlation coefficient: r=0.2188; P<0.01). The ratio of TT3 to TT4 in Table 5 show a generally decrease at d 20, increase at d 30, 60 and 90 in LI and HiF groups. And the ratio of TT3 to TT4 was decreased at d 20, 30 and 90, but increased at d 60 in the LI and HiF groups.
DISCUSSION The development of the thyroid gland in offspring rats exposed to HiF and LI The thyroid gland is one of the important endocrine glands, which is tied with brain development. Iodine
Table 1 Ratio of thyroid weight to body weight (g kg-1) in offspring rats induced by high fluoride and low iodine Days after birth (d) 10 20 30 60 90 Mean values
Control
Low iodine (LI)
High fluoride (HiF)
High fluoride and low iodine (HiF+LI)
0.14±0.05 A 0.09±0.04 B 0.11±0.03 A 0.06±0.01 B 0.09±0.07 A 0.10±0.05 A
0.14±0.01 A 0.18±0.04 A 0.12±0.01 A 0.06±0.01 AB 0.07±0.03 A 0.11±0.05 A
0.09±0.04 A 0.13±0.01 AB 0.12±0.02 A 0.07±0.01 A 0.06±0.02 A 0.09±0.03 A
0.12±0.05 0.16±0.01 0.16±0.07 0.07±0.01 0.06±0.02 0.11±0.05
A A A A A A
Capital letters show P<0.05; small letters show P<0.01. The means for the treated and the control groups were analyzed at different ages. Means with the same letters are not significantly different. Data are means±SD. The same as below.
Table 2 The level of TT3 in serum induced by high fluoride and low iodine (ng mL-1) Days after birth (d) 20 30 60 90 Mean values
Control
Low iodine (LI)
1.18±0.48 A 1.18±0.26 Bb 0.93±0.08 B 0.77±0.21 A 1.00±0.37 Bb
1.37±0.33 A 1.96±0.18 Aa 1.23±0.33 AB 0.94±0.10 A 1.30±0.09Aa
High fluoride (HiF) 1.13±0.27 A 1.79±0.15 Aab 1.32±0.08 A 1.13±0.17 A 1.31±0.34 Aa
High fluoride and low iodine (HiF+LI) 0.61±0.14 B 1.59±0.23 ABab 1.19±0.15 AB 0.72±0.17 A 1.11±0.10 Bab
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Table 3 The level of TT4 in serum induced by high fluoride and low iodine (ng mL-1) Days after birth (d) 20 30 60 90 Mean values
Control 46.62±6.18 B 35.07±5.08 Bb 48.57±7.45 A 48.65±14.52 A 45.64±10.57 Bb
Low iodine (LI) 66.91±5.36 A 49.85±8.27 Aa 47.18±10.08 A 45.08±8.31 A 50.98±11.37 ABab
High fluoride (HiF) 70.81±15.81 A 47.90±10.67 Aa 56.77±5.14 A 51.82±17.02 A 56.46±15.77 Aa
High fluoride and low iodine (HiF+LI) 54.65±0.07 AB 47.45±9.61 Aa 52.32±20.95 A 47.11±9.47 A 49.76±13.44 ABab
Table 4 The level of TSH in serum induced by high fluoride and low iodine (IU mL-1) Days after birth (d) 20 30 60 90 Mean values
Control
Low iodine (LI)
High fluoride (HiF)
2.31±0.29 Cb 2.14±0.44 Aa 3.14±0.67 A 3.43±0.69 A 2.79±0.75 A
2.56±0.47 BCb 0.50±0.25 Cb 1.67±0.51 A 3.38±0.67 A 2.29±0.34 A
3.98±1.56 Bab 1.31±0.47 Bab 2.56±1.92 A 2.82±0.51 A 2.53±0.41 A
Fig. The correlation TT3 and TT4 in serum induced by high fluoride and low iodine correlation coefficient, r=0.2188; P<0.01.
deficiency is known to induce goiter and even cretinism, especially in the developing brain. In the present study, goiter induced by iodine deficiency was observed and the relative weight of the thyroid gland in the LI group was added at d 20 and 30 compared to the control group. But their relative weights were lower at d 90. Iodine deficiency can induce functional compensation of the thyroid and induce compensatory hyperplasia of the thyroid. This action was most evident at d 20. Subsequently, compensatory hyperplasia began to weaken. Long term excess fluoride intake can induce goiter and the dysfunction of the thyroid gland (PFPC 2002). Lu et al. (2001) reported that the thyroid structure of chicken with long term exposure to fluoride was destructed. The thyroid gland was atrophic in the early stage and was swollen with gummosity and nodule. Some studies reported that thyroid structures changed and their volume and weight had no marked change
High fluoride and low iodine (HiF+LI) 5.65±1.26 Aa 1.92±0.52 ABa 2.97±0.22 A 2.87±0.43 A 2.89±0.26 A
(Lu et al. 1996). In this study, the relative weight of the thyroid gland in offspring rats showed the decreaseincrease-decrease tendency from 10 to 90 d compared to control group, indicating that time is an important factor that affects thyroid exposure to excess fluoride. Zhao et al. (1998) reported that the absolute thyroid weight of mice treated with low iodine, high fluoride or both together for 100 d were increased, especially in the HiF+LI group, but no difference in relative thyroid weight was found, since the body weight of mice increased simultaneously. In the present study, the absolute thyroid weight was also increased during the early time, especially 20-d-old offspring rats in the HiF+LI group. However, owing to a little increase in body weight, relative thyroid weight significantly increased at d 20 and 60 in the HiF+LI group. Up to d 90, relative thyroid weight showed a decreasing trend, due to a much greater decrease in absolute thyroid weight than in the absolute body weight.
Thyroid function of offspring rats exposed to HiF and LI Iodine is a major materials to produce thyroid hormone. The ratio of T4 and T3 secreted by the thyroid gland is about 10:1. Circulating T4 was wholly secreted by the thyroid gland, but the major source of circulating T3 (80-90%) was from peripheral deiodination of T4 and not from thyroid secretion. Thyroid stimulating hormone, abbreviated as TSH, can stimulate the thyroid gland and excite follicular cells that secrete thyroid hormone (T3 and T4). The process is regulated by a
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Effects of High Fluoride and Low Iodine on Thyroid Function in Offspring Rats
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Table 5 The ratio of TT3/TT4 in serum induced by high fluoride and low iodine (TT3/TT4×10-2) Days after birth (d) 20 30 60 90 Mean values
Control
Low iodine (LI)
High fluoride (HiF)
2.27±0.39 A 3.29±0.86 A 1.94±0.36 A 1.62±0.24 A 2.16±0.83 A
2.11±0.27 AB 3.82±0.88 A 2.75±0.48 A 2.05±0.16 A 2.59±0.19 A
1.68±0.57 AB 3.77±0.60 A 2.36±0.34 A 3.01±0.93 A 2.72±0.36 A
negative feedback mechanism, i.e., when the pituitary gland senses a drop in FT3 levels in circulation, it releases more TSH to stimulate the thyroid gland which in turn accelerates the production of the thyroid hormone T4. At last, circulating T3 was elevated by deiodination of T4 in peripheral tissue (Markh and Robert 2001). It was proved further by the correlation between T3 and T4 in serum induced by high fluoride, low iodine or both together (r=0.2188; P<0.01). Of course, the key factor, deiodinases, play vital roles in the process. Deiodinases, namely D1, D2, and D3, regulate the homeostasis of thyroid hormone. D1 is known to be responsible for the conversion of T4 to T3 in peripheral tissues, particularly in the liver, and is reflected in plasma T3 levels (Susheela et al. 2005). D2 is the key enzyme responsible for modifying systemic T3 levels from T4 transform, and its activity decreases as T3/T4 levels decline (O’Barr et al. 2006). Thus, D2 converts T4 into the biologically active T3, while D3 catalyzes the conversion of T4 into 3,3´,5´-triiodothyronine (reverse T3=rT3), and of T3 into 3,3´diiodothyronine (3,3´-T2), both of which are biologically inactive. Thyroid hormones play crucial roles in regulating development, differentiation, and metabolism of almost every tissue in the body of mammals, including teeth, bone and brain (Schuld 2005; Zhan et al. 2006). In the present study, the serum TT3 levels in Table 2 show a significant decrease at d 20 in the LI and HiF groups, generally increase at d 30 and 60 in three groups. Serum TT4 levels in Table 3 show a generally increase at d 20 and 30, and serum TSH data in Table 4 shows a generally increase only at d 20, decrease at d 30, then an increased trend to come extent in three groups compared to the controls. Those results suggest that iodine deficiency or high fluoride or both might trigger the feedback mechanism of the thyroid hormone. The pituitary secretes more TSH to stimulate the thyroid gland and strengthen thyroid function, and more circuiting
High fluoride and low iodine (HiF+LI) 1.11±0.27 B 3.21±0.42 A 2.47±0.28 A 1.53±0.27 A 2.17±0.87 A
T4 was secreted by follicular cells. So an increase in serum TSH at d 20 and in serum TT4 at d 20 and 30 in offspring rats were observed in this present study. Further more, circuiting elevated TT3 in 20-, 30- and 60-d-old rats may be attributed to increase TT4 at 20and 30-d, which can be seen that T4 was deiodinated and changed into active T3 by deiodinase in order to supply T3 in circulation. Owing to durative iodine deficiency or high fluoride, the negative feedback mechanism of the thyroid gland was aggravated and levels of TSH began decreasing descent at d 30. Then secretion of thyroid follicular cells was weakened. At d 60, serum TT4 dropped and the degree of increase in TT3 was also decreased. TT3 decrease induced by the interaction of iodine deficiency and high fluoride was seen at d 20, but TT3 decrease induced by the interaction of iodine deficiency or high fluoride was not seen during 20-90 d. In addition, in this process, D2 is the key enzyme responsible for modifying systemic T3 levels, which has been observed. Fluoride may depress D2 activity and induce a decrease in TT3 at d 20. A significant decrease of TT3/TT4 value at d 20 supports the above observation. But there was a reversed state in the next stage of the HiF group. There was another important explanation that fluoride is an established TSH analogue, as documented in many laboratory investigations (PFPC 2007). Fluoride therefore has the ability, like TSH, to influence all aspects of thyroid hormone homeostasis in all tissue where the TSH receptor is expressed, not only the thyroid, which has been long believed, but many other tissue, including bone (Abe et al. 2003) and brain (Saunier et al. 1993; Crisanti et al. 2001). And some reported that TSH-regulated pathways are more responsive to fluoride activation than TSH itself (PFPC 2007). So, in this study, increase in serum TT3 and TT4 was observed at all experimental periods in the HiF group except for a decrease in TT3 at d 20. At d 90, the ratio of
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TT3/TT4 was raised sharply in the HiF group. These results showed that fluoride, as a TSH analogue, can activate the secretion of TT4 and activity of D2 under this condition. It is different from the results reported by Zhao et al. (1998) that fluoride, as TSH analogue, caused an increase in TT4 on normal iodine, while at the same time caused a decrease in TT3. Tezelman et al. (1994) reported that even a small increase in adenylate cyclase/cAMP is sufficient to desensitize the TSH receptor, which may be achieved by either TSH or F. It is generally accepted that low concentrations of TSH (<0.2 mIU mL-1) exert a positive control on TSH receptor numbers at the surface of thyrocytes, whereas high concentrations (>0.2 mIU mL-1) lead to partial desensitization. A prolonged increase in cAMP leads to inhibition of iodination in humans. Decreased TSH receptor sensitivity would also inhibit activation of the D2 deiodinase, resulting in decreased TT3 and TT4 levels of 90-d-old rats in the HiF+LI group than before. Numerous studies on the effects of fluoride on thyroid function have been conducted on humans and animals. But, the reported results were different. A tendency to increased iodine uptake, reduced TT3 and increased TSH were found by Bachinski et al. (1985) in people living in a high fluoride area, with (122±5) mol L-1 (about 2.3 ppm) in the water, compared to those in a control area with (52±5) mol L-1 (about 1.0 ppm). In contrast, TT4 level were decreased and level of TT3 and TSH were increased in 8-12-yr old children living in high fluoride area with 3.52 mg L-1 in the water (Liu et al. 1998). In addition, NaF-treated pups from the 15th d of pregnancy to the 14th d after delivery (NaF in drinking water 0.5 g L -1), at age 14 d after birth, showed a 15% decrease in plasma-free T4 and a 6% decrease in plasma-free T3, compared to a control group (Bouaziz et al. 2005). Decreases in TT3 and TT4 have been found after the administration of fluoride to animals (Guan et al. 1988; Wang et al. 2009), including in a study by Yu (1985) where 50 ppm of fluoride in the drinking water of rats reduced the serum TT3 and TT4. In all these above studies, T3, T4 and TSH in serum were determined only once during the stage of exposure to high fluoride. But this study observed a dynamic change of the thyroid hormone in serum in offspring rats exposed to
high fluoride in order to assess effect of high fluoride on thyroid function. Zhao et al. (1988) reported that serum TT3 and TT4 in mice treated with iodine deficiency and fluoride excess for 100 d (TT3: (1.52±0.33) ng mL-1; TT4: (116±15.13) ng mL-1) were higher than those with iodine normal and fluoride excess (TT3: (0.95±0.09) ng mL-1; TT4: (101.6±18.36) ng mL -1). But, after 150 d, the decrease of TT4 in all iodine deficiency groups was much more remarkable irrespective of fluorine intake (the average values were 5.0 to 9.6 g mL-1) (Zhao et al. 1988, 1998). Similar results were observed in this study. In view of these results, exposure time to flroride or low iodine diet is one of the important factors to induce the development of thyroid disorder. Some studies have shown that damage of the thyroid gland and derangement of thyroid function were induced by excess fluoride. When ingesting low iodine or decreasing in the ingestion function of the thyroid gland, the adverse effect of fluoride in excess on thyroid gland was more evident. It had been reported that the rate and degree of the incisor fluorosis were significantly higher in the iodine deficiency and fluoride excess group than those in the iodine normal and fluoride excess group (Zhao et al. 1988, 1998). Susheela et al. (2005) even found that iodine supplementation may not be adequate to reduce iodine deficiency disorders (IDD) when excess fluoride is being consumed. Removal of fluoride from ingestion needs to precede iodine supplementation. In the present study, an evident increase in serum TSH at d 20, a marked decrease in serum TT3 at d 20 and an increase in serum TT4 before d 60 are shown in Tables 2-4 in the HiF+LI group. From the mean values in TT3, TT4 and TSH, the damage degree of thyroid function in the HiF+LI group were not more serious, compared to the HiF group and the LI group respectively.
CONCLUSION In summary, this study demonstrated that the perturbations of thyroid hormone levels were induced by HiF, LI or both together. Exposure time to fluoride or low iodine diet was one of the important factors that fluoride can induce the development of thyroid dyfunction.
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Effects of High Fluoride and Low Iodine on Thyroid Function in Offspring Rats
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Breeding of iodine-deficient offspring rats
MATERIALS AND METHODS
As in our recent reports (Wang et al. 2004a, b; Ge et al. 2005a, b, c, 2006), 1-mon-old Wister albino rats, each weighing approximately 50 g, were obtained from the Experimental Animal Center of Shanxi Medical University, China, for study. The experimental iodine-deficient diet was made from wheat, corn and soybean grown in an iodine-deficient region - Weijiawan Village of Anze County in Shanxi Province. The normal diet was provided by the Experimental Animal Center of Shanxi Medical University. The contents of iodine and fluoride in the experimental feed and in the control feed are listed in Table 6.
Establishment of test animal model Thirty-two one-mon-old Wistar albino rats (female:male=3:1) were randomly divided into four groups of six females and two males each and were maintained on the diets and water regimens shown in the Table 6 under standard temperature (22-25°C), ventilation, and hygienic conditions.
Three mon after establishing the animal model, the female experimental animals were allowed to become pregnant by natural mating. The day of the birth of their offspring was set as d 0. During and after nursing, the pups were raised under the same conditions as their parents. At d 20, three male and three female offspring rats were randomly selected from each litter for further study.
Assays of TT3, TT4 and TSH The pups of the control and treated rats were anaesthetized with intra-abdominal 20% urethane solution on postnatal d 10, 20, 30, 60, and 90. The body weights were measured and bloods were got by extirpating the eyeball. Then blood from the pups was centrifuged at 2 200×g and the plasma samples were kept at -20°C until the total T4 (TT4), total T3 (TT3) and TSH were measured by radioimmunoassay (note: the blood of 10-d-old rats were too little to measure TT4, TT3 and TSH). The pups were sacrificed after blood samples and the thyroid glands were collected. Statistical analysis of the means for the treated and the control groups was done with Duncan’s test.
Table 6 Fluorine in the drinking water (mg F- L-1) and fluoride and iodine levels in the diet (mg kg-1) of the rats Control Iodine in diet Fluorine in diet Fluorine in drinking water 1)
0.3543 25.57 <0.6
High fluoride (HiF)
Low iodine (LI)
0.3543 25.57 451)
0.0855 26.01 <0.6
High fluoride and low iodine (HiF+LI) 0.0855 26.01 451)
From 100 mg NaF L-1 (it had been recorded in our previous reports (Ge et al. 2006)).
Acknowledgements This research was sponsored by the National Natural Science Foundation of China (30170681) and the Foundation of Henan Institute of Science and Technology, China (6007).
References Abe E, Marians R C, Yu W, Wu X B, Ando T, Li Y, Iqbal J, Eldeiry L, Rajendren G, Blair H C, et al. 2003. TSH is a negative regulator of skeletal remodeling. Cell, 115, 151162. Bachinskii P P, Gutsakeko O A, Narysaniur N D, Aidora V D, Shliakhta A. 1985. Action of the body fluorine of healthy persons and thyroidopathy patients on the function of hypophyseal-thyroid system. Problemy Endokrinologii, 31, 25-29. Beers M H, Berkow R. 2001. The Merck Manual of Diagnosis and Therapy. 17th ed. Translated by Xue C L. People’s Medical Publishing House, Beijing. Bouaziz H, Soussia L, Guermazi F, Zeghal N. 2005. Fluoride-
induced thyroid proliferative changes and their reversal in female mice and their pups. Fluoride, 38, 185-192. Crisanti P, Omri B, Hughes E, Meduri G, Hery C, Clauser E, Jacquemin C, Saunier B. 2001. The expression of thyrotropin receptor in the brain. Endocrinology, 142, 812-822. Ge Y M, Ning H M, Feng C P, Wang H W, Yan X Y, Wang S L, Wang J D. 2006. Apoptosis in brain cells of offspring rat exposed to high fluoride and low iodine. Fluoride, 39, 173-178. Ge Y M, Ning H M, Wang S L, Wang J D. 2005a. Effects of high fluoride and low iodine on brain histopathology in offspring rats. Fluoride, 38, 127-132. Ge Y M, Ning H M, Wang S L, Wang J D. 2005b. Comet assay of DNA damage in brain cells of adult rats exposed to high fluoride and low iodine. Fluoride, 38, 209-214. Ge Y M, Ning H M, Wang S L, Wang J D. 2005c. DNA damage in thyroid gland cells of rats exposed to longterm intake of high fluoride and low iodine. Fluoride, 38, 318-323. Guan Z Z, Zhuang Z J, Yang P S, Pan S. 1988. Synergistic
© 2013, CAAS. All rights reserved. Published by Elsevier Ltd.
508
action of iodine deficiency and fluorine intoxication on rat thyroid. Chinese Medical Journal, 101, 679-694. (in Chinese) Hong F G, Cao Y X, Yang D, Wang H. 2001. The effect of fluoride on intelligence of children exposed to different environments. Chinese Primary Health Care, 15, 5657. (in Chinese) Kang S L, Liu G. 2002. Effects of fluoride on ultrastructure of thyroid mitochondria in chicks. Journal of Shanghai Jiaotong University (Agricultural Sciences), 20, 224227. (in Chinese) Lin F F, Aihaiti, Zhao H X, Lin J, Jiang J Y, Maimaiti, Aiken. 1991. The relationship of a low-iodine and high-fluoride environment to subclinical cretinism in Xinjiang. Iodine Deficiency Disorder Newsletter, 7, 24-25. Liu G. 2002. Effects of fluoride on the ultrastructure of chicken thyroid tissue. Chinese Veterinary Science, 22, 512-514. (in Chinese) Liu X L, Fan Z X, Hua J L, Wu H Y, Wang Q S. 1998. Mensuration of T3, T4 and TSH in children in endemic fluorosis area. Chinese Journal of Control of Endemic Diseases, 13, 359-360. (in Chinese) Lu C H, Bian J C, Ye P. 1996. The effect of fluoride on pituitary, thyroid and parathyroid gland in rats. Chinese Journal of Control of Endemic Diseases, 11, 18-21. (in Chinese) Lu G Y, Chai C Y, Kang S L. 2001. The effect of fluoride on thyroid structure in chicken. Chinese Journal of Endemiology, 20, 90-93. (in Chinese) O’Barr S A, Oh J S, Ma C, Brent G A, Schultz J J. 2006. Thyroid hormone regulates endogenous amyloid-b precursor protein gene expression and processing in both in vitro and in vivo models. Thyroid, 16, 12071213. Parents of Fluoride Poisoned Children (PFPC). 2002. History of the fluoride/iodine antagonism. [2005-06-14]. http:// www.bruha.com/pfpc/html/thyroid_history.html Parents of Fluoride Poisoned Children (PFPC). 2007. Vancouver c1995-2007.Fluoride=TSH. [2009-08-09]. http://poisonfluoride.com/Science/TSH/tsh.html Saunier B, Pierre M, Jacquemin C, Courtin F. 1993. Evidence for cAMP-independent thyrotropin effects on astroglial cells. European Journal of Biochemistry, 218, 1091-
GE Ya-ming et al.
1094. Schuld A. 2005. Is dental fluorosis caused by thyroid hormone disturbances? Fluoride, 38, 91-94. Steyn D G, Kieser J, Odendaal W A, Malherbe H, Snyman H W, Sunkel W, Naude C P, Klintworth H, Fisher E. 1955. Endemic goiter in the union of south Africa and some neighbouring territories. [2005-03-01]. http://www. fluoridealert.org/health/thyroid/ steyn-1955.html Susheela A K, Bhatnagar M, Vig K, Mondal N K. 2005. Excess fluoride ingestion and thyroid hormone derangements in children living in delhi, india. Fluoride, 38, 98-108. Tezelman S, Shaver J K, Grossman R F, Liang W, Siperstein A E, Duh Q Y, Clark O H. 1994. Desensitization of adenylate cyclase in Chinese hamster ovary cells transfected with human thyroid-stimulating hormone receptor. Endocrinology, 134, 1561-1569. Wang J D, Ge Y M, Ning H M, Wang S L. 2004a. Effects of high fluoride and low iodine on biochemical indexes of the brain and learning-memory of offspring rats. Fluoride, 37, 201-208. Wang J D, Ge Y M, Ning H M, Wang S L. 2004b. Effect of high fluoride and low iodine on oxidative stress and antioxidant defense of the brain in offspring rats. Fluoride, 37, 264-270. Wang H, Yang Z, Zhou B, Gao H, Yan X, Wang J. 2009. Fluoride-induced thyroid dysfunction in rats: roles of dietary protein and calcium level. Toxicology and Industrial Health, 25, 49-57. Yu Y N. 1985. Effects of chronic fluorosis in the thyroid gland. National Medical Journal of China, 65, 747749. (in Chinese) Zhan X A, Li J X, Wang M, Xu Z R. 2006. Effects of fluoride on growth and thyroid function in young pigs. Fluoride, 39, 95-100. Zhao W, Zhu H, Yu Z, Aoki K, Misumi J, Zhang X. 1998. Long-term effects of various iodine and fluorine doses on the thyroid and fluorosis in mice. Endocrine Regulationsm, 32, 63-70. Zhao W Y, Zhu H M, Hu X Y. 1988. A preliminary study of iodide and fluoride in experimental goiter and fluorosis. Chinese Journal of Preventive Medicine, 22, 146-148. (in Chinese) (Managing editor ZHANG Juan)
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March 2013
2013, 12(3): 502-508
RESEARCH ARTICLE
Effects of High Fluoride and Low Iodine on Thyroid Function in Offspring Rats GE Ya-ming1, 2*, NING Hong-mei1, 2*, GU Xin-li3, YIN Mei1, YANG Xue-feng1, QI Yong-hua1 and WANG Jundong2 College of Animal Science, Henan Institute of Science and Technology, Xinxiang 453003, P.R.China Shanxi Key Laboratory of Ecological Animal Science and Environmental Medicine, Shanxi Agricultural University, Taigu 030801, P.R.China 3 College of Animal Science and Technology, Shihezi University, Shihezi 832000, P.R.China 1 2
Abstract Thirty-two Wistar rats were divided randomly into four groups of eight with six females and two males in each group. The rats were exposed to high fluoride drinking water (45 mg F- L-1 from 100 mg NaF L-1), low dietary iodine (0.0855 mg kg-1), or both together in order to assess the effects of these three regimens on the thyroid function of the offspring rats. After the animal model was established, the offspring rats were bred and 10-, 20-, 30-, 60-, and 90-d-old rats were used for the experiment. The treatments for the offspring rats were the same as those of their parents. In comparison with control rats, the relative thyroid glands were changed by three regimens, but the mean values of thyroid weight in the experimental groups saw no marked difference. Serum TT3 levels were increased in all stages in the low iodine (LI) group. In the high fluoride (HiF) group, increase in TT3 levels was observed except in 20-d-old rats. Decrease in TT3 at 20- and 90-d and increase in TT3 at 30- and 60-d were found in HiF+LI group. Serum TT4 levels first saw an increase, and then dropped in the LI and HiF+LI group. However, an increase in TT4 was found in the HiF group. The levels of TSH in serum rocketed at d 20, and then dropped in the next stages in experimental groups. The results suggested that thyroid disorder could be induced by high flroride in drinking water, low iodine diet, or both of them. Exposure time to fluoride or low iodine diet was one of the important factors that fluoride can induce the development of thyroid dyfunction. Key words: high fluoride, iodine deficiency, offspring rats, thyroid function
INTRODUCTION Fluorosis is one of the most frequently occurring endemic diseases. Their main clinical statuses were dental and skeletal fluorosis. In recent years, epidemiological investigations have revealed that fluorosis and iodine deficiency have co-existed in developing countries, such as China (Lin et al. 1991; Hong et al. 2001), and India (Susheela et al. 2005). The incidence Received 21 October, 2011
rates of hypothyroidism goiter and cretinism in areas of both high fluoride (HiF) and low iodine (LI) were higher than those in low fluoride areas (Lin et al. 1991; Hong et al. 2001). Fluoride can not only induce damage of hard tissue in the body, but also injure soft tissue in the body. As early as in 1936, several cases of endemic goitre in European women on farms in the districts of South Africa were reported. But that area was known to be iodine-rich, and that area is a known endemic fluorine area. So this halogen (fluoride) was im-
Accepted 23 March, 2012
GE Ya-ming, E-mail: [email protected]; Correspondence WANG Jun-dong, E-mail: [email protected] * These authors contributed equally to this study. © 2013, CAAS. All rights reserved. Published by Elsevier Ltd. doi:10.1016/S2095-3119(13)60251-8
Effects of High Fluoride and Low Iodine on Thyroid Function in Offspring Rats
mediately suspected and considered as one of the main factors inducing goiter prevalence in that area (Steyn et al. 1955). Excess fluoride can accumulate in the thyroid gland, affecte iodine metabolism of thyroid follicle cells, disturb synthesis and secretion of thyroid hormone, and then induce incidence of goiter. But time is an important factor for fluoride damage to the thyroid gland (Liu 2002; Kang and Liu 2002). On the basis of our conducted studies on the brains of young offspring rats when exposed to HiF, LI, or both regimens together in the early stages of development (Wang et al. 2004a, b; Ge et al. 2005a, b, c, 2006), we assessed the effects of HiF, LI, and their combination on thyroid function in offspring rats in the present study.
RESULTS The development of the thyroid gland in offspring rats The ratio of thyroid weight to body weight in offspring rats in controls and experimental groups are shown in Table 1. Compared to the control group, the thyroid gland in low iodine groups (LI) were no change at day 10, were swelled at d 20 and 30, and then thyroid gland began to shrink at d 60 and 90. The trend in HiF and HiF+LI groups showed that the thyroid gland was atrophic at first, swelled and then atrophied from d 10 to 90. But the mean values of thyroid weight in experimental groups had no marked difference.
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Thyroid hormone levels in serum The levels of TT3, TT4 and TSH in serum from the offspring rats according to their treatments are listed in Tables 2-4, respectively. Compared to the control group, the serum TT3 levels in Table 2 show a significant decrease at d 20 in the LI and HiF groups (P<0.05), generally increase at d 30 and 60 in three experimental groups, especially in HiF group (P<0.05). Serum TT4 levels in Table 3 show a generally increase at d 20 and 30 in experimental groups, especially at d 30 (P<0.01). And serum TSH data in Table 4 shows a generally increase only at d 20, decrease at d 30, 60 and 90 in experimental groups. Fig. shows the correlation between TT3 and TT4 in serum induced by high fluoride and low iodine (correlation coefficient: r=0.2188; P<0.01). The ratio of TT3 to TT4 in Table 5 show a generally decrease at d 20, increase at d 30, 60 and 90 in LI and HiF groups. And the ratio of TT3 to TT4 was decreased at d 20, 30 and 90, but increased at d 60 in the LI and HiF groups.
DISCUSSION The development of the thyroid gland in offspring rats exposed to HiF and LI The thyroid gland is one of the important endocrine glands, which is tied with brain development. Iodine
Table 1 Ratio of thyroid weight to body weight (g kg-1) in offspring rats induced by high fluoride and low iodine Days after birth (d) 10 20 30 60 90 Mean values
Control
Low iodine (LI)
High fluoride (HiF)
High fluoride and low iodine (HiF+LI)
0.14±0.05 A 0.09±0.04 B 0.11±0.03 A 0.06±0.01 B 0.09±0.07 A 0.10±0.05 A
0.14±0.01 A 0.18±0.04 A 0.12±0.01 A 0.06±0.01 AB 0.07±0.03 A 0.11±0.05 A
0.09±0.04 A 0.13±0.01 AB 0.12±0.02 A 0.07±0.01 A 0.06±0.02 A 0.09±0.03 A
0.12±0.05 0.16±0.01 0.16±0.07 0.07±0.01 0.06±0.02 0.11±0.05
A A A A A A
Capital letters show P<0.05; small letters show P<0.01. The means for the treated and the control groups were analyzed at different ages. Means with the same letters are not significantly different. Data are means±SD. The same as below.
Table 2 The level of TT3 in serum induced by high fluoride and low iodine (ng mL-1) Days after birth (d) 20 30 60 90 Mean values
Control
Low iodine (LI)
1.18±0.48 A 1.18±0.26 Bb 0.93±0.08 B 0.77±0.21 A 1.00±0.37 Bb
1.37±0.33 A 1.96±0.18 Aa 1.23±0.33 AB 0.94±0.10 A 1.30±0.09Aa
High fluoride (HiF) 1.13±0.27 A 1.79±0.15 Aab 1.32±0.08 A 1.13±0.17 A 1.31±0.34 Aa
High fluoride and low iodine (HiF+LI) 0.61±0.14 B 1.59±0.23 ABab 1.19±0.15 AB 0.72±0.17 A 1.11±0.10 Bab
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Table 3 The level of TT4 in serum induced by high fluoride and low iodine (ng mL-1) Days after birth (d) 20 30 60 90 Mean values
Control 46.62±6.18 B 35.07±5.08 Bb 48.57±7.45 A 48.65±14.52 A 45.64±10.57 Bb
Low iodine (LI) 66.91±5.36 A 49.85±8.27 Aa 47.18±10.08 A 45.08±8.31 A 50.98±11.37 ABab
High fluoride (HiF) 70.81±15.81 A 47.90±10.67 Aa 56.77±5.14 A 51.82±17.02 A 56.46±15.77 Aa
High fluoride and low iodine (HiF+LI) 54.65±0.07 AB 47.45±9.61 Aa 52.32±20.95 A 47.11±9.47 A 49.76±13.44 ABab
Table 4 The level of TSH in serum induced by high fluoride and low iodine (IU mL-1) Days after birth (d) 20 30 60 90 Mean values
Control
Low iodine (LI)
High fluoride (HiF)
2.31±0.29 Cb 2.14±0.44 Aa 3.14±0.67 A 3.43±0.69 A 2.79±0.75 A
2.56±0.47 BCb 0.50±0.25 Cb 1.67±0.51 A 3.38±0.67 A 2.29±0.34 A
3.98±1.56 Bab 1.31±0.47 Bab 2.56±1.92 A 2.82±0.51 A 2.53±0.41 A
Fig. The correlation TT3 and TT4 in serum induced by high fluoride and low iodine correlation coefficient, r=0.2188; P<0.01.
deficiency is known to induce goiter and even cretinism, especially in the developing brain. In the present study, goiter induced by iodine deficiency was observed and the relative weight of the thyroid gland in the LI group was added at d 20 and 30 compared to the control group. But their relative weights were lower at d 90. Iodine deficiency can induce functional compensation of the thyroid and induce compensatory hyperplasia of the thyroid. This action was most evident at d 20. Subsequently, compensatory hyperplasia began to weaken. Long term excess fluoride intake can induce goiter and the dysfunction of the thyroid gland (PFPC 2002). Lu et al. (2001) reported that the thyroid structure of chicken with long term exposure to fluoride was destructed. The thyroid gland was atrophic in the early stage and was swollen with gummosity and nodule. Some studies reported that thyroid structures changed and their volume and weight had no marked change
High fluoride and low iodine (HiF+LI) 5.65±1.26 Aa 1.92±0.52 ABa 2.97±0.22 A 2.87±0.43 A 2.89±0.26 A
(Lu et al. 1996). In this study, the relative weight of the thyroid gland in offspring rats showed the decreaseincrease-decrease tendency from 10 to 90 d compared to control group, indicating that time is an important factor that affects thyroid exposure to excess fluoride. Zhao et al. (1998) reported that the absolute thyroid weight of mice treated with low iodine, high fluoride or both together for 100 d were increased, especially in the HiF+LI group, but no difference in relative thyroid weight was found, since the body weight of mice increased simultaneously. In the present study, the absolute thyroid weight was also increased during the early time, especially 20-d-old offspring rats in the HiF+LI group. However, owing to a little increase in body weight, relative thyroid weight significantly increased at d 20 and 60 in the HiF+LI group. Up to d 90, relative thyroid weight showed a decreasing trend, due to a much greater decrease in absolute thyroid weight than in the absolute body weight.
Thyroid function of offspring rats exposed to HiF and LI Iodine is a major materials to produce thyroid hormone. The ratio of T4 and T3 secreted by the thyroid gland is about 10:1. Circulating T4 was wholly secreted by the thyroid gland, but the major source of circulating T3 (80-90%) was from peripheral deiodination of T4 and not from thyroid secretion. Thyroid stimulating hormone, abbreviated as TSH, can stimulate the thyroid gland and excite follicular cells that secrete thyroid hormone (T3 and T4). The process is regulated by a
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Table 5 The ratio of TT3/TT4 in serum induced by high fluoride and low iodine (TT3/TT4×10-2) Days after birth (d) 20 30 60 90 Mean values
Control
Low iodine (LI)
High fluoride (HiF)
2.27±0.39 A 3.29±0.86 A 1.94±0.36 A 1.62±0.24 A 2.16±0.83 A
2.11±0.27 AB 3.82±0.88 A 2.75±0.48 A 2.05±0.16 A 2.59±0.19 A
1.68±0.57 AB 3.77±0.60 A 2.36±0.34 A 3.01±0.93 A 2.72±0.36 A
negative feedback mechanism, i.e., when the pituitary gland senses a drop in FT3 levels in circulation, it releases more TSH to stimulate the thyroid gland which in turn accelerates the production of the thyroid hormone T4. At last, circulating T3 was elevated by deiodination of T4 in peripheral tissue (Markh and Robert 2001). It was proved further by the correlation between T3 and T4 in serum induced by high fluoride, low iodine or both together (r=0.2188; P<0.01). Of course, the key factor, deiodinases, play vital roles in the process. Deiodinases, namely D1, D2, and D3, regulate the homeostasis of thyroid hormone. D1 is known to be responsible for the conversion of T4 to T3 in peripheral tissues, particularly in the liver, and is reflected in plasma T3 levels (Susheela et al. 2005). D2 is the key enzyme responsible for modifying systemic T3 levels from T4 transform, and its activity decreases as T3/T4 levels decline (O’Barr et al. 2006). Thus, D2 converts T4 into the biologically active T3, while D3 catalyzes the conversion of T4 into 3,3´,5´-triiodothyronine (reverse T3=rT3), and of T3 into 3,3´diiodothyronine (3,3´-T2), both of which are biologically inactive. Thyroid hormones play crucial roles in regulating development, differentiation, and metabolism of almost every tissue in the body of mammals, including teeth, bone and brain (Schuld 2005; Zhan et al. 2006). In the present study, the serum TT3 levels in Table 2 show a significant decrease at d 20 in the LI and HiF groups, generally increase at d 30 and 60 in three groups. Serum TT4 levels in Table 3 show a generally increase at d 20 and 30, and serum TSH data in Table 4 shows a generally increase only at d 20, decrease at d 30, then an increased trend to come extent in three groups compared to the controls. Those results suggest that iodine deficiency or high fluoride or both might trigger the feedback mechanism of the thyroid hormone. The pituitary secretes more TSH to stimulate the thyroid gland and strengthen thyroid function, and more circuiting
High fluoride and low iodine (HiF+LI) 1.11±0.27 B 3.21±0.42 A 2.47±0.28 A 1.53±0.27 A 2.17±0.87 A
T4 was secreted by follicular cells. So an increase in serum TSH at d 20 and in serum TT4 at d 20 and 30 in offspring rats were observed in this present study. Further more, circuiting elevated TT3 in 20-, 30- and 60-d-old rats may be attributed to increase TT4 at 20and 30-d, which can be seen that T4 was deiodinated and changed into active T3 by deiodinase in order to supply T3 in circulation. Owing to durative iodine deficiency or high fluoride, the negative feedback mechanism of the thyroid gland was aggravated and levels of TSH began decreasing descent at d 30. Then secretion of thyroid follicular cells was weakened. At d 60, serum TT4 dropped and the degree of increase in TT3 was also decreased. TT3 decrease induced by the interaction of iodine deficiency and high fluoride was seen at d 20, but TT3 decrease induced by the interaction of iodine deficiency or high fluoride was not seen during 20-90 d. In addition, in this process, D2 is the key enzyme responsible for modifying systemic T3 levels, which has been observed. Fluoride may depress D2 activity and induce a decrease in TT3 at d 20. A significant decrease of TT3/TT4 value at d 20 supports the above observation. But there was a reversed state in the next stage of the HiF group. There was another important explanation that fluoride is an established TSH analogue, as documented in many laboratory investigations (PFPC 2007). Fluoride therefore has the ability, like TSH, to influence all aspects of thyroid hormone homeostasis in all tissue where the TSH receptor is expressed, not only the thyroid, which has been long believed, but many other tissue, including bone (Abe et al. 2003) and brain (Saunier et al. 1993; Crisanti et al. 2001). And some reported that TSH-regulated pathways are more responsive to fluoride activation than TSH itself (PFPC 2007). So, in this study, increase in serum TT3 and TT4 was observed at all experimental periods in the HiF group except for a decrease in TT3 at d 20. At d 90, the ratio of
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TT3/TT4 was raised sharply in the HiF group. These results showed that fluoride, as a TSH analogue, can activate the secretion of TT4 and activity of D2 under this condition. It is different from the results reported by Zhao et al. (1998) that fluoride, as TSH analogue, caused an increase in TT4 on normal iodine, while at the same time caused a decrease in TT3. Tezelman et al. (1994) reported that even a small increase in adenylate cyclase/cAMP is sufficient to desensitize the TSH receptor, which may be achieved by either TSH or F. It is generally accepted that low concentrations of TSH (<0.2 mIU mL-1) exert a positive control on TSH receptor numbers at the surface of thyrocytes, whereas high concentrations (>0.2 mIU mL-1) lead to partial desensitization. A prolonged increase in cAMP leads to inhibition of iodination in humans. Decreased TSH receptor sensitivity would also inhibit activation of the D2 deiodinase, resulting in decreased TT3 and TT4 levels of 90-d-old rats in the HiF+LI group than before. Numerous studies on the effects of fluoride on thyroid function have been conducted on humans and animals. But, the reported results were different. A tendency to increased iodine uptake, reduced TT3 and increased TSH were found by Bachinski et al. (1985) in people living in a high fluoride area, with (122±5) mol L-1 (about 2.3 ppm) in the water, compared to those in a control area with (52±5) mol L-1 (about 1.0 ppm). In contrast, TT4 level were decreased and level of TT3 and TSH were increased in 8-12-yr old children living in high fluoride area with 3.52 mg L-1 in the water (Liu et al. 1998). In addition, NaF-treated pups from the 15th d of pregnancy to the 14th d after delivery (NaF in drinking water 0.5 g L -1), at age 14 d after birth, showed a 15% decrease in plasma-free T4 and a 6% decrease in plasma-free T3, compared to a control group (Bouaziz et al. 2005). Decreases in TT3 and TT4 have been found after the administration of fluoride to animals (Guan et al. 1988; Wang et al. 2009), including in a study by Yu (1985) where 50 ppm of fluoride in the drinking water of rats reduced the serum TT3 and TT4. In all these above studies, T3, T4 and TSH in serum were determined only once during the stage of exposure to high fluoride. But this study observed a dynamic change of the thyroid hormone in serum in offspring rats exposed to
high fluoride in order to assess effect of high fluoride on thyroid function. Zhao et al. (1988) reported that serum TT3 and TT4 in mice treated with iodine deficiency and fluoride excess for 100 d (TT3: (1.52±0.33) ng mL-1; TT4: (116±15.13) ng mL-1) were higher than those with iodine normal and fluoride excess (TT3: (0.95±0.09) ng mL-1; TT4: (101.6±18.36) ng mL -1). But, after 150 d, the decrease of TT4 in all iodine deficiency groups was much more remarkable irrespective of fluorine intake (the average values were 5.0 to 9.6 g mL-1) (Zhao et al. 1988, 1998). Similar results were observed in this study. In view of these results, exposure time to flroride or low iodine diet is one of the important factors to induce the development of thyroid disorder. Some studies have shown that damage of the thyroid gland and derangement of thyroid function were induced by excess fluoride. When ingesting low iodine or decreasing in the ingestion function of the thyroid gland, the adverse effect of fluoride in excess on thyroid gland was more evident. It had been reported that the rate and degree of the incisor fluorosis were significantly higher in the iodine deficiency and fluoride excess group than those in the iodine normal and fluoride excess group (Zhao et al. 1988, 1998). Susheela et al. (2005) even found that iodine supplementation may not be adequate to reduce iodine deficiency disorders (IDD) when excess fluoride is being consumed. Removal of fluoride from ingestion needs to precede iodine supplementation. In the present study, an evident increase in serum TSH at d 20, a marked decrease in serum TT3 at d 20 and an increase in serum TT4 before d 60 are shown in Tables 2-4 in the HiF+LI group. From the mean values in TT3, TT4 and TSH, the damage degree of thyroid function in the HiF+LI group were not more serious, compared to the HiF group and the LI group respectively.
CONCLUSION In summary, this study demonstrated that the perturbations of thyroid hormone levels were induced by HiF, LI or both together. Exposure time to fluoride or low iodine diet was one of the important factors that fluoride can induce the development of thyroid dyfunction.
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Effects of High Fluoride and Low Iodine on Thyroid Function in Offspring Rats
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Breeding of iodine-deficient offspring rats
MATERIALS AND METHODS
As in our recent reports (Wang et al. 2004a, b; Ge et al. 2005a, b, c, 2006), 1-mon-old Wister albino rats, each weighing approximately 50 g, were obtained from the Experimental Animal Center of Shanxi Medical University, China, for study. The experimental iodine-deficient diet was made from wheat, corn and soybean grown in an iodine-deficient region - Weijiawan Village of Anze County in Shanxi Province. The normal diet was provided by the Experimental Animal Center of Shanxi Medical University. The contents of iodine and fluoride in the experimental feed and in the control feed are listed in Table 6.
Establishment of test animal model Thirty-two one-mon-old Wistar albino rats (female:male=3:1) were randomly divided into four groups of six females and two males each and were maintained on the diets and water regimens shown in the Table 6 under standard temperature (22-25°C), ventilation, and hygienic conditions.
Three mon after establishing the animal model, the female experimental animals were allowed to become pregnant by natural mating. The day of the birth of their offspring was set as d 0. During and after nursing, the pups were raised under the same conditions as their parents. At d 20, three male and three female offspring rats were randomly selected from each litter for further study.
Assays of TT3, TT4 and TSH The pups of the control and treated rats were anaesthetized with intra-abdominal 20% urethane solution on postnatal d 10, 20, 30, 60, and 90. The body weights were measured and bloods were got by extirpating the eyeball. Then blood from the pups was centrifuged at 2 200×g and the plasma samples were kept at -20°C until the total T4 (TT4), total T3 (TT3) and TSH were measured by radioimmunoassay (note: the blood of 10-d-old rats were too little to measure TT4, TT3 and TSH). The pups were sacrificed after blood samples and the thyroid glands were collected. Statistical analysis of the means for the treated and the control groups was done with Duncan’s test.
Table 6 Fluorine in the drinking water (mg F- L-1) and fluoride and iodine levels in the diet (mg kg-1) of the rats Control Iodine in diet Fluorine in diet Fluorine in drinking water 1)
0.3543 25.57 <0.6
High fluoride (HiF)
Low iodine (LI)
0.3543 25.57 451)
0.0855 26.01 <0.6
High fluoride and low iodine (HiF+LI) 0.0855 26.01 451)
From 100 mg NaF L-1 (it had been recorded in our previous reports (Ge et al. 2006)).
Acknowledgements This research was sponsored by the National Natural Science Foundation of China (30170681) and the Foundation of Henan Institute of Science and Technology, China (6007).
References Abe E, Marians R C, Yu W, Wu X B, Ando T, Li Y, Iqbal J, Eldeiry L, Rajendren G, Blair H C, et al. 2003. TSH is a negative regulator of skeletal remodeling. Cell, 115, 151162. Bachinskii P P, Gutsakeko O A, Narysaniur N D, Aidora V D, Shliakhta A. 1985. Action of the body fluorine of healthy persons and thyroidopathy patients on the function of hypophyseal-thyroid system. Problemy Endokrinologii, 31, 25-29. Beers M H, Berkow R. 2001. The Merck Manual of Diagnosis and Therapy. 17th ed. Translated by Xue C L. People’s Medical Publishing House, Beijing. Bouaziz H, Soussia L, Guermazi F, Zeghal N. 2005. Fluoride-
induced thyroid proliferative changes and their reversal in female mice and their pups. Fluoride, 38, 185-192. Crisanti P, Omri B, Hughes E, Meduri G, Hery C, Clauser E, Jacquemin C, Saunier B. 2001. The expression of thyrotropin receptor in the brain. Endocrinology, 142, 812-822. Ge Y M, Ning H M, Feng C P, Wang H W, Yan X Y, Wang S L, Wang J D. 2006. Apoptosis in brain cells of offspring rat exposed to high fluoride and low iodine. Fluoride, 39, 173-178. Ge Y M, Ning H M, Wang S L, Wang J D. 2005a. Effects of high fluoride and low iodine on brain histopathology in offspring rats. Fluoride, 38, 127-132. Ge Y M, Ning H M, Wang S L, Wang J D. 2005b. Comet assay of DNA damage in brain cells of adult rats exposed to high fluoride and low iodine. Fluoride, 38, 209-214. Ge Y M, Ning H M, Wang S L, Wang J D. 2005c. DNA damage in thyroid gland cells of rats exposed to longterm intake of high fluoride and low iodine. Fluoride, 38, 318-323. Guan Z Z, Zhuang Z J, Yang P S, Pan S. 1988. Synergistic
© 2013, CAAS. All rights reserved. Published by Elsevier Ltd.
508
action of iodine deficiency and fluorine intoxication on rat thyroid. Chinese Medical Journal, 101, 679-694. (in Chinese) Hong F G, Cao Y X, Yang D, Wang H. 2001. The effect of fluoride on intelligence of children exposed to different environments. Chinese Primary Health Care, 15, 5657. (in Chinese) Kang S L, Liu G. 2002. Effects of fluoride on ultrastructure of thyroid mitochondria in chicks. Journal of Shanghai Jiaotong University (Agricultural Sciences), 20, 224227. (in Chinese) Lin F F, Aihaiti, Zhao H X, Lin J, Jiang J Y, Maimaiti, Aiken. 1991. The relationship of a low-iodine and high-fluoride environment to subclinical cretinism in Xinjiang. Iodine Deficiency Disorder Newsletter, 7, 24-25. Liu G. 2002. Effects of fluoride on the ultrastructure of chicken thyroid tissue. Chinese Veterinary Science, 22, 512-514. (in Chinese) Liu X L, Fan Z X, Hua J L, Wu H Y, Wang Q S. 1998. Mensuration of T3, T4 and TSH in children in endemic fluorosis area. Chinese Journal of Control of Endemic Diseases, 13, 359-360. (in Chinese) Lu C H, Bian J C, Ye P. 1996. The effect of fluoride on pituitary, thyroid and parathyroid gland in rats. Chinese Journal of Control of Endemic Diseases, 11, 18-21. (in Chinese) Lu G Y, Chai C Y, Kang S L. 2001. The effect of fluoride on thyroid structure in chicken. Chinese Journal of Endemiology, 20, 90-93. (in Chinese) O’Barr S A, Oh J S, Ma C, Brent G A, Schultz J J. 2006. Thyroid hormone regulates endogenous amyloid-b precursor protein gene expression and processing in both in vitro and in vivo models. Thyroid, 16, 12071213. Parents of Fluoride Poisoned Children (PFPC). 2002. History of the fluoride/iodine antagonism. [2005-06-14]. http:// www.bruha.com/pfpc/html/thyroid_history.html Parents of Fluoride Poisoned Children (PFPC). 2007. Vancouver c1995-2007.Fluoride=TSH. [2009-08-09]. http://poisonfluoride.com/Science/TSH/tsh.html Saunier B, Pierre M, Jacquemin C, Courtin F. 1993. Evidence for cAMP-independent thyrotropin effects on astroglial cells. European Journal of Biochemistry, 218, 1091-
GE Ya-ming et al.
1094. Schuld A. 2005. Is dental fluorosis caused by thyroid hormone disturbances? Fluoride, 38, 91-94. Steyn D G, Kieser J, Odendaal W A, Malherbe H, Snyman H W, Sunkel W, Naude C P, Klintworth H, Fisher E. 1955. Endemic goiter in the union of south Africa and some neighbouring territories. [2005-03-01]. http://www. fluoridealert.org/health/thyroid/ steyn-1955.html Susheela A K, Bhatnagar M, Vig K, Mondal N K. 2005. Excess fluoride ingestion and thyroid hormone derangements in children living in delhi, india. Fluoride, 38, 98-108. Tezelman S, Shaver J K, Grossman R F, Liang W, Siperstein A E, Duh Q Y, Clark O H. 1994. Desensitization of adenylate cyclase in Chinese hamster ovary cells transfected with human thyroid-stimulating hormone receptor. Endocrinology, 134, 1561-1569. Wang J D, Ge Y M, Ning H M, Wang S L. 2004a. Effects of high fluoride and low iodine on biochemical indexes of the brain and learning-memory of offspring rats. Fluoride, 37, 201-208. Wang J D, Ge Y M, Ning H M, Wang S L. 2004b. Effect of high fluoride and low iodine on oxidative stress and antioxidant defense of the brain in offspring rats. Fluoride, 37, 264-270. Wang H, Yang Z, Zhou B, Gao H, Yan X, Wang J. 2009. Fluoride-induced thyroid dysfunction in rats: roles of dietary protein and calcium level. Toxicology and Industrial Health, 25, 49-57. Yu Y N. 1985. Effects of chronic fluorosis in the thyroid gland. National Medical Journal of China, 65, 747749. (in Chinese) Zhan X A, Li J X, Wang M, Xu Z R. 2006. Effects of fluoride on growth and thyroid function in young pigs. Fluoride, 39, 95-100. Zhao W, Zhu H, Yu Z, Aoki K, Misumi J, Zhang X. 1998. Long-term effects of various iodine and fluorine doses on the thyroid and fluorosis in mice. Endocrine Regulationsm, 32, 63-70. Zhao W Y, Zhu H M, Hu X Y. 1988. A preliminary study of iodide and fluoride in experimental goiter and fluorosis. Chinese Journal of Preventive Medicine, 22, 146-148. (in Chinese) (Managing editor ZHANG Juan)
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