2017: Effects of F on thyroid and intelligence in rats

All adverse health effects of fluoride are related to thyroid hormone metabolism.
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2017: Effects of F on thyroid and intelligence in rats

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Cui YS, Zhong Q, Li WF, Liu ZH, Wang Y, Hou CC - "Effects of fluoride exposure on thyroid hormone level and intelligence in rats" Chinese Journal of Industrial Hygiene and Occupational Diseases 35(12):888-892 (2017)
doi: 10.3760/cma.j.issn.1001-9391.2017.12.002
https://www.ncbi.nlm.nih.gov/pubmed/29495148

Objective: To investigate the effects of fluoride exposure on the thyroid hormone
level and intelligence in rats and to investigate the biomarkers of intellectual
impairment induced by high fluoride exposure. Methods: A total of 24 clean
healthy Sprague-Dawley rats were randomly divided into control group (tap water
containing 0.344 mg/L fluoride) and low-, medium-, and high-fluoride exposure
groups (tap waters containing 10, 50, and 100 mg/L sodium fluoride,
respectively). One male rat was cohabited with two female rats in the same group.
After the offspring rats were weaned, 12 offspring rats (male/female ratio=1∶1)
with a similar body weight in each group were subjected to the same treatment for
the parental offspring. The offspring rats were sacrificed on the 60th day after
birth. The weight of offspring rats was measured. Serum thyrotropin (TSH) , free
triiodothyronine (FT(3)) , and free thyroxine (FT(4)) levels were measured by
enzyme-linked immunosorbent assay. The learning and memory abilities of the rats
were evaluated by Morris water maze test. The expression of mitochondrial fission
1 (Fis1) and mitofusin 1 (Mfn1) in blood was measured by Western blot. Results:
The offspring rats in the medium-and high-fluoride exposure groups had
significantly lower serum TSH and FT(4) levels than those in the control group
(P<0.05). The place navigation test showed that the offspring rats in the
medium-and high-fluoride exposure groups had significantly longer escape latency
than those in the control group (P<0.05) , and the high-fluoride exposure group
had a significantly longer escape distance than those in the control group
(P<0.05). The spatial probe test showed that the offspring rats in the low-,
medium-, and high-fluoride exposure groups had significantly shorter swimming
time and distance in the target quadrant and total swimming time and distance
than those in the control group (P<0.05). Compared with the offspring rats in the
control group, those in the low-, medium-, and high-fluoride exposure groups had
significantly higher expression of Fis1 (P<0.05) , and those in the low- and
medium-fluoride exposure groups had significantly higher expression of Mfn1
(P<0.05) . Conclusion: High fluoride exposure can reduce the secretion of thyroid
hormone and the abnormality of mitochondrial dynamics in peripheral lymphocytes
may provide a clue to identifying the biomarkers of intellectual impairment
induced by fluoride exposure.
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