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Estrogen increases thyroid function. Wtf?

From: http://www.biomedcentral.com/1756-0500/2/173

"Effects of chronic estradiol treatment on the thyroid gland structure and function of ovariectomized rats

Abstract

Background

Estrogen therapy is widely used nowadays in women to treat many postmenopausal symptoms but it may have some undesirable effects due to multiple organs affection. So, the aim of this study was to determine the effects of chronic estradiol treatment on the structure and function of the thyroid gland in ovarictomized rats as a model simulating menopause.

Findings

Thirty adult female Wistar rats divided into three groups were used in this study; the first group was sham-operated, while the second and third groups were ovariectomized. The first and second groups were injected with olive oil while the third group was injected with estradiol dipropionate daily for three months, after that; hormonal assay for T3, T4, TSH and specimens of the thyroid were taken and processed to be examined by light and electron microscopy. The results of this study revealed that serum levels of T3 and T4 decreased in ovariectomized animals and significantly increased after estradiol treatment, while TSH increased in ovariectomized animals and decreased with estradiol treatment. Histological and morphometric study in ovariectomized group revealed marked accumulation of colloid in follicular lumens with decreased epithelial height in addition to increased connective tissue amount. After estradiol treatment the follicles became smaller in size, having small amount of colloid with increased epithelial height in addition to decreased connective tissue content. Ultrastructural study supported these results in addition to the presence of large amount of intracytoplasmic colloid vesicles after estradiol treatment.

Conclusion

Low estrogen level may lead to mild thyroidal hypofunction while estradiol treatment may lead to hyperactivity so it should be used very cautiously in the treatment of postmenopausal symptoms to avoid its undesirable stimulatory effect on the thyroid."
asked Apr 16, 2015 by freshness

1 Answer

The only thing out of the ordinary in this study, is the level of influence estrogen had on thyroid function, as can be seen in table 1 of the study (http://www.biomedcentral.com/1756-0500/2/173/table/T1).
Estrogen replacement has been repeately found to normalize T3 levels in ovariectomized rats while increasing thyroid weight, altough modulatory effects on TSH and T4 are rarely found.
Estrogen increases the levels of TPO (thyroperoxidase) in the thyroid, an enzyme that allows tyrosine residues to be iodinated. (http://www.ncbi.nlm.nih.gov/pubmed/16762383?dopt=Abstract&holding=f1000,f1000m,isrctn)

Conversely, chronic estradiol treatment has been found to decrease T3 and T4 levels and cause hyperplasia of the thyroid gland in non-ovariectomized rats. (http://www.ncbi.nlm.nih.gov/pubmed/15637454?dopt=Abstract&holding=f1000,f1000m,isrctn)
answered Apr 16, 2015 by Dewitt
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