Prolonged hypothyroidism severely reduces ovarian follicular reserve in adult rats

A Review of Autoimmune Thyroid Diseases and Their Complex Interplay with Female Fertility

Hashimoto thyroiditis and Graves' disease are autoimmune thyroid disorders that are common in women of reproductive age and have a complex relationship with female fertility and health of the maternal-fetal dyad. Both hyperthyroidism and hypothyroidism, whether subclinical or overt in severity, directly or indirectly affect nearly every level of the hypothalamic-pituitary-ovary axis, uterine and ovarian function, as well as fetal development from implantation through delivery. Autoimmunity itself also appears to negatively impact both spontaneous and assisted fertility, as well as miscarriage risk, although the mechanism remains unclear, and the presence and magnitude of risk is variable in published literature. While treatment of overt hyperthyroidism and hypothyroidism is unequivocally recommended by professional societies, the impact of treatment on fertility outcomes, and the role of treatment in subclinical thyroid disease is more controversial. Unfortunately, levothyroxine has not been shown to abrogate the risk of subfertility and miscarriage observed in euthyroid thyroid autoantibody positive women.

Arsenic-Induced Thyroid Hormonal Alterations and Their Putative Influence on Ovarian Follicles in Balb/c Mice

Thyroid issues are common among women in their reproductive years, and women with thyroid dysfunction often encounter challenges with fertility. Arsenic is known for its toxic effects on the thyroid and ovaries, investigated independently. However, there is no known study directly or indirectly addressing the association between arsenic, thyroid function, and ovarian reserve. This study aims to investigate the effect of arsenic on thyroid function and its possible implications on ovarian follicular reserve. Female Balb/c mice were given sodium arsenite (0.2 ppm, 2 ppm, and 20 ppm) via drinking water for 30 days. Findings showed that arsenic decreased thyroid hormone levels (fT3 and fT4) while increasing TSH levels, which might have led to elevated levels of FSH and LH. Furthermore, arsenic treatment not only decreased thyroid follicle sizes but also altered the ovarian follicular count. The finding demonstrates that arsenic significantly reduced the expression of LAMP1, a lysosomal marker protein. This reduction leads to increased lysosomal permeability in the thyroid, resulting in a significant release of cathepsin B. These changes led to hypothyroidism, which might indirectly affect the ovaries. Also, the elevated levels of growth differentiation factor-8 in arsenic-treated ovaries indicate impaired folliculogenesis and ovulation. Furthermore, arsenic significantly increased the expressions of pAkt and pFoxo3a, implying that arsenic accelerated the activation of the primordial follicular pools. In conclusion, arsenic disrupts lysosomal stabilization, potentially leading to a decline in circulating fT3 and fT4 levels. This disturbance could, in turn, affect the estrous cycle and may alter the pattern of follicular development.

Effects of acute hypothyroidism on plasma melatonin and Aanat and Asmt expression in the pineal gland and gonads of rats

Introduction

The reproductive system is tightly regulated by environmental and physiological signals. Melatonin, known as the hormone of darkness, plays a crucial role in regulating both the circadian and reproductive systems in mammals. Hypothyroidism is a key endocrine disorder that harms the reproductive system. Despite many studies on melatonin's effects on the reproductive system, there is conflicting information regarding melatonin synthesis modulation in hypothyroidism. The objective of this study was to investigate the modulation of plasma melatonin levels and gene expression of Aanat and Asmt in the pineal gland and gonads of rats with hypothyroidism at different times of the day.

Methods

Female and male Wistar rats were divided into control and hypothyroid groups. Hypothyroidism was induced using propylthiouracil (PTU) for 15 days, rats were euthanized six hours after lights on (ZT6), before lights off (ZT11.5), and six hours after lights off (ZT18). Free thyroxine (FT4) and melatonin were quantified in plasma, and gene expressions of melatonin synthesizing enzymes (Aanat and Asmt) were measured in pineal and sexual organs (testis and ovary). Also, morphological analysis was performed in sexual organs.

Results

The results reveal some disparities between the sexes. Hypothyroidism reduced antral and primary follicles in the ovary, and reduced the weight of testis, epididymis, and prostate. In relation to gene expression, we observed a reduction in Aanat expression in the pineal gland during the light phase (ZT6), and in males, this reduction occurred during the dark phase (ZT18). Regarding Asmt expression, there was a decrease in females also during the dark phase (ZT18). In the gonads, there was an increase in expression in both sexes at ZT11.5. Additionally, it was interesting to observe the association between FT4 levels and Asmt expression in the gonads.

Conclusions

This study showed that acute hypothyroidism can affect components of the melatonergic system in gonads, particularly gene expression of melatonin synthesis enzymes (Aanat and Asmt) contributing to changes in reproduction organs during disease progression. These findings enhance our understanding of melatonin synthesis in the reproductive system during hypothyroidism, showing distinct responses in male and female rats, and suggest that hypothyroidism affects the circadian rhythmicity of melatonin synthesis in a sex-dependent manner.

Protective effect of thyroid and restores of ovarian function of Buzhong Yiqi granule on experimental autoimmune thyroiditis in female rats

OBJECTIVE

To observe the effects of Buzhong Yiqi granule on thyroid function and ovarian function in rats with experimental autoimmune thyroiditis (EAT).

METHODS

EAT model was replicate by using the method of mixing and injecting porcine thyroglobulin with Freund's adjuvant and high iodine. Rats were randomly divided into normal control (NC) group, EAT model (EAT) group, selenium yeast (PC) group, low dose Buzhong Yiqi (BZYQ-L) group, medium dose Buzhong Yiqi (BZYQ-M) group and high dose Buzhong Yiqi (BZYQ-H) group. After two months of drug intervention according to dosage, enzyme-linked immunosorbent assay (ELISA) was used to measure the levels of free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), anti-thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TGAb) in peripheral blood of rats. The pathological changes of rat thyroid tissues were observed under light microscope with HE staining; ELISA was used to determine estradiol (E2), follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), anti-müllerian hormone (AMH), and the pathological changes of rat ovarian tissues were observed under light microscope with hematoxylin and eosin staining.

RESULTS

Compared with the NC group, BZYQ granule improved the thyroid and ovarian tissue morphology, and the levels of TPOAb, TGAb and TSH in the model group rats significantly increased (P < 0.05), the thyroid tissue was severely destroyed, the levels of E2, FSH, LH, T, AMH significantly increased (P < 0.05), and the ovary exhibited polycystic changes; Compared with the model group, TSH level in the BZYQ-L group rats decreased (P < 0.05), FSH, T, AMH levels decreased (P < 0.05), in the BZYQ-M group TPOAb, TSH levels decreased (P < 0.05), FSH, LH, T, AMH levels significantly decreased (P < 0.05), BZYQ-H group TPOAb, TGAb, TSH levels significantly decreased (P < 0.05), FSH, LH, T, AMH levels significantly decreased (P < 0.05), with the greatest improvement and significantly better than selenium yeast group (P < 0.05).

CONCLUSIONS

BZYQ granule could regulate the thyroid function of EAT rats, reduce thyroid antibody titers, then act on the ovarian function, regulate hormone disorders, and alleviate the pathological damage of rat's ovarian tissues. The effect of high dose Buzhong Yiqi granule is the best.

Disruption of Thyroid Hormone Receptor Thrab Leads to Female Infertility in Zebrafish

Thyroid hormones (THs) T4 and T3 are vital for development, growth, and metabolism. Thyroid dysfunction can also cause problems in fertility, suggesting involvement of THs in reproduction. In zebrafish, there exist 2 forms of TH receptor alpha gene (thraa and thrab). Disruption of these genes by CRISPR/Cas9 showed no reproductive irregularities in the thraa mutant; however, inactivation of the thrab gene resulted in female infertility. Although young female mutants (thrabm/m) showed normal ovarian development and folliculogenesis before sexual maturation, they failed to release eggs during oviposition after sexual maturation. This spawning failure was due to oviductal blockage at the genital papilla. The obstruction of the oviduct subsequently caused an accumulation of the eggs in the ovary, resulting in severe ovarian hypertrophy, abdominal distention, and disruption of folliculogenesis. Gene expression analysis showed expression of both TH receptors and estrogen receptors in the genital papilla, suggesting a direct TH action and potential interactions between thyroid and estrogen signaling pathways in controlling genital papilla development and function. In addition to their actions in the reproductive tracts, THs may also have direct effects in the ovary, as suggested by follicle atresia and cessation of folliculogenesis in the heterozygous mutant (thrab+/m), which was normal in all aspects of female reproduction in young and sexually mature fish but exhibited premature ovarian failure in aged females. In summary, this study provides substantial evidence for roles of THs in controlling the development and functions of both reproductive tract and ovary.

Elevated Thyroglobulin Antibody Level is Associated with Decreased Anti-Müllerian Hormone in Women of Reproductive Age

Purpose

Women with Hashimoto's thyroiditis (HT) have an increased risk of ovarian insufficiency. However, whether thyroid antibodies affect the ovarian reserve remains controversial. The aim of this study was to explore the possible relationship between anti-Müllerian hormone (AMH) and thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) levels in women of reproductive age.

Methods

A total of 483 women between 18 and 45 years old who had their TPOAb, TgAb, thyroid-stimulating hormone (TSH), free thyroxine (FT4), and AMH levels measured on the same day were enrolled in this study. The levels of TSH, FT4, TPOAb, and TgAb, the prevalence of overt and subclinical hypothyroidism, and the positive rate of TPOAb and TgAb were compared between patients with low (below the 10th percentile), normal (10th to 90th percentile), and high (higher than the 90th percentile) AMH levels.

Results

The median AMH level was 1.72 (0.33-4.27) ng/mL. A total of 9.9% of patients had low AMH levels. The TgAb levels and the prevalence of TgAb positivity were higher in the low AMH group (37.62 (13.10-232.68) IU/mL, 35.42%) than in the normal (12.46 (10.0-67.04) IU/mL, 19.59%) and high (13.61 (10.0-95.74) IU/mL, 23.4%) AMH groups (p=0.001, p=0.040, respectively). Serum AMH levels were inversely correlated with TgAb levels (r = -0.114, p=0.013).

Conclusion

The AMH of women of reproductive age is affected by HT. Furthermore, women with the lowest AMH level had higher levels of TgAb and a positive rate of TgAb, and high TgAb levels may cause autoimmune damage to the ovaries.

The Thyroid Hormone Axis and Female Reproduction

Thyroid function affects multiple sites of the female hypothalamic-pituitary gonadal (HPG) axis. Disruption of thyroid function has been linked to reproductive dysfunction in women and is associated with menstrual irregularity, infertility, poor pregnancy outcomes, and gynecological conditions such as premature ovarian insufficiency and polycystic ovarian syndrome. Thus, the complex molecular interplay between hormones involved in thyroid and reproductive functions is further compounded by the association of certain common autoimmune states with disorders of the thyroid and the HPG axes. Furthermore, in prepartum and intrapartum states, even relatively minor disruptions have been shown to adversely impact maternal and fetal outcomes, with some differences of opinion in the management of these conditions. In this review, we provide readers with a foundational understanding of the physiology and pathophysiology of thyroid hormone interactions with the female HPG axis. We also share clinical insights into the management of thyroid dysfunction in reproductive-aged women.

Radioactive Iodine-induced hypothyroidism interferes with the maturation of reproductive organs during puberty in immature female rats

Animal and human studies suggest that thyroid hormone may have critical roles in the development of the ovary. For example, thyroid deficiency disrupts the ovarian microarchitecture and menstrual cycle in neonate and adult women, respectively. Therefore, it is conceivable that thyroid deficiency might disrupt sexual maturation during the peri-pubertal period. To investigate the impact of radioactive iodine-induced thyroid deficiency on reproductive organs throughout puberty, immature female rats were given water containing radioactive iodine (0.37 MBq/g body weight) twice, on postnatal days 22 and 29. Radioactive iodine-induced hypothyroidism was revealed by low free thyroxin levels. Thyroid deficiency delayed the onset of vaginal opening, reduced ovarian weight and the number of medium-sized follicles and led to elongated uteri. However, there was no effect on the estrous cycle or absolute uterus weight. We conclude that radioactive iodine-induced thyroid deficiency delays sexual maturation and alters normal ovarian growth in peri-pubertal rats.

IFN-γ differential expression in the hypothalamus-pituitary-ovary axis of thyroidectomized rats

IFN-γ is critical for both thyroid and ovarian function, while thyroxine, secreted from the thyroid gland, regulates the ovarian function via the hypothalamus-pituitary -ovary axis. However, the effect of thyroxine on INF-γ involved in the regulation of hypothalamic pituitary ovarian axis ovarian function is hitherto unknown. Therefore, we set up three groups including a sham-operated group, an experimental thyroidectomized group, and an experimental thyroidectomized group treated with T4 to reveal the IFN-γ expression levels in the in the hypothalamus, pituitary gland, and ovary by immunohistochemical staining, RT-PCR, and Western blotting. IFN-γ-like immunoreactive-positive substances were visualized in the hypothalamus, pituitary gland, and ovary, which were located mainly in the cytoplasm of the hypothalamic neurons anterior pituitary cells, luteal cells, and theca cells in the ovary of hypothyroidism rats, respectively. RT-PCR and Western blotting showed that the rats in the experimental thyroidectomized group treated with T4 had significantly elevated expression of IFN-γ at both the mRNA and protein levels. Thyroxine affects the expression of IFN-γ in the thalamus-pituitary-ovarian axis, which may influence the secretion of IFN-γ to regulate ovarian function during hypothyroidism. This work highlights the potential effect of thyroxine on the involvement of INF-γ in the modulation of the ovarian function in the hypothalamic-pituitary-ovarian axis.

Kisspeptin Treatment Restores Ovarian Function in Rats with Hypothyroidism

Background: Hypothyroidism causes ovarian dysfunction and infertility in women, in addition to being associated with hyperprolactinemia and reduced hypothalamic expression of kisspeptin (Kp). However, it remains unknown whether and how Kp is able to reverse the ovarian dysfunction caused by hypothyroidism. Methods: Hypothyroidism was induced in adult female Wistar rats using 6-propyl-2-thiouracil for 3 months. In the last month, half of the animals received Kp10. Blood samples were collected for dosage of free thyroxine, thyrotropin (TSH), luteinizing hormone (LH), prolactin (PRL), progesterone (P₄), and estradiol (E₂), and uteruses and ovaries were collected for histomorphometry. Body and ovarian weight and the number of corpora lutea were also evaluated. Half of the brains were evaluated by immunohistochemistry to Kp, and the other half had the arcuate nucleus of hypothalamus (ARC) and preoptic area microdissected for gene evaluation of Kiss1, Nkb, Pdyn, and Gnrh1. The pituitary gland and corpora lutea were also dissected for gene evaluation. Results: Hypothyroidism kept the animals predominantly acyclic and promoted a reduction in ovarian weight, number of corpora lutea, endometrial thickness, number of endometrial glands, and plasma LH, in addition to increasing the luteal messenger RNA (mRNA) expression of Star and Cyp11a1 and reducing 20αHsd. An increase in plasma PRL and P₄ levels was also caused by hypothyroidism. Kp immunoreactivity and Kiss1 and Nkb mRNA levels in the ARC and Kiss1 in the anteroventral periventricular nucleus of hypothalamus were reduced in hypothyroid rats. Hypothyroid animals had lower pituitary gene expression of Gnrhr, Lhb, Prl, and Drd2, and an increase in Tshb. The treatment with Kp10 restored estrous cyclicality, plasma LH, ovarian and uterine morphology, and Cyp11a1, 3βHsd, and 20αHsd mRNA levels in the corpora lutea. Kp10 treatment did not alter gene expression for Kiss1 or Nkb in the ARC of hypothyroid rats. Nevertheless, Kp10 increased Lhb mRNA levels and reduced Tshb in the pituitary compared with the hypothyroid group. Conclusions: The present findings characterize the inhibitory effects of hypothyroidism on the hypothalamic-pituitary-gonadal axis in female rats and demonstrate that Kp10 is able to reverse the ovarian dysfunction caused by hypothyroidism, regardless of hyperprolactinemia.

Effect of hypothyroidism and thyroid autoimmunity on the ovarian reserve: A systematic review and meta-analysis

Background

Evidence suggests that hypothyroidism and thyroid autoimmunity (TAI) are possibly associated with ovarian dysfunction. This meta‐analysis aimed to investigate whether hypothyroidism and/or TAI affect the ovarian reserve and evaluated using the anti‐Mullerian hormone (AMH).

Methods

PubMed, EMBASE, Web of Science, and Cochrane Controlled Trials Register databases from inception to October 2020 were searched to identify relevant studies. Studies comparing the AMH levels between the control and the affected groups were included in the data synthesis. The primary endpoint in the meta‐analysis was AMH levels compared with the controls.

Main findings

Nine trials were included in the analysis. The AMH levels were significantly lower in the adults with euthyroid TAI (mean difference −0.12, [95% CI: −0.18 to −0.06]). The AMH levels tended to be lower in subclinical hypothyroidism and overt hypothyroidism than in the control group, although the differences were not significant. The AMH levels were significantly higher in the euthyroid TAI group in the adolescents (mean difference 2.51, [95% CI 1.82 to 3.21]).

Conclusion

TAI and hypothyroidism may affect the ovarian reserve. The opposite effects on AMH levels depending on age suggest that TAI may be implicated in the depletion of follicles in adults following extensive activation of primordial follicles in adolescence.

Association between thyroid autoimmunity and ovarian reserve in women with hypothyroidism

Background

The ovarian function and therefore the ovarian reserve may be compromised by the pathogenesis of autoimmune diseases of which, Hashimoto’s thyroiditis (HT) is the most common in women of reproductive age. Furthermore, a prolonged reduction in thyroid hormone concentration results in a broad spectrum of reproductive alteration. Previous reports in the literature have been controversial regarding the impact of hypothyroidism and alterations in the ovarian reserve. Thus, this prospective and comparative study aimed to evaluate the association of hypothyroidism with low ovarian reserve.

Materials and Methods

A subset of 27 patients with primary autoimmune hypothyroidism were compared to healthy women. The ovarian reserve was assessed through the anti-Mullerian hormone (AMH) and the antral follicle count (AFC).

Results

Overall, the two groups did not display significant differences in length of their menstrual cycles neither in the AMH serum levels nor the AFC.

Conclusions

No significant alteration was found in the ovarian reserve of women with HT.

Melatonin on hypothyroidism and gonadal development in rats: a review

We evaluated the evidence in research on the effects of melatonin on hypothyroidism and gonadal development. According to the World Health Organization, thyroid disorders due to iodine deficiency affect about 740 million people worldwide. Hypothyroidism is a thyroid dysfunction characterized by hypometabolism of the gland, with reduced or physiologically normal T3 and T4 serum levels, and high TSH level. This disorder occurs mainly in adult women in the reproductive phase, with a prevalence of 2% among the world's female population, with profound repercussions on gestation and fetal formation. During the gestational period, the thyroid is initially stimulated by high concentrations of human chorionic gonadotrophin; thus, maintaining maternal euthyroidism during pregnancy and lactation is fundamental for fetal growth and development. Besides, the hormones produced by this gland are involved in the formation of various organs, such as the skin, brain and gonads. Hypothyroidism is associated with several menstrual abnormalities, anovulation and hyperprolactinemia, resulting in a high rate of abortions, premature births, placental rupture, and weight-related neonatal deficits. In addition, there are studies showing that hypothyroidism can affect ovarian morphology (number of ovarian follicles) and testicular morphology (changes in the testicular-lumen epithelium). Melatonin is a hormone known to modulate the estrous cycle and pregnancy, and studies show that the exogenous application of melatonin increased T4 levels in female rats and controlled the decrease in T3 serum levels, reverting the sigs of hypothyroidism.

The efficacy of acupuncture for the treatment and the fertility improvement in child-bearing period female with Hashimoto Disease: A randomized controlled study

BACKGROUND

Hashimoto thyroiditis (HT) is highly prevalent among reproductive-aged women and has a substantial negative impact on fertility. Currently, there is no specific treatment for Hashimoto thyroiditis. We hypothesize that acupuncture can halt or delay the progression of HT and improve fertility in child-bearing period female. We therefore designed a randomized controlled trial to test this hypothesis by comparing the therapeutic effect of acupuncture vs sham acupuncture in patients with Hashimoto thyroiditis.

METHODS

In this randomized controlled study, a total of 284 eligible patients will be assigned to acupuncture group (n = 142) or sham acupuncture group (n = 142) in a 1:1 ratio. All patients will receive 36 sessions in total for 12 consecutive weeks with the same acupoint prescription (RN23, ST9, RN17, RN4, RN6, ST36, SP6, KI6). The primary assessment is the titers of thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibody (TGAb). Secondary outcomes include the thyroid function, ovarian function, the rate of primary ovarian insufficiency, and pregnancy outcome. The thyroid function and thyroid antibodies tests will be measured at weeks 0, 4, 8, and 12 after randomization. The ovarian function will be examined on the 2nd to 4th day of the menstrual period in the 1st month, 2nd month and 3rd month compared with baseline. Both the pregnancy outcome and the rate of primary ovarian insufficiency will be evaluated 1 year after treatment.

DISCUSSION

This will be the first large-scale trial specifically evaluating acupuncture therapy in child-bearing period female with Hashimoto thyroiditis. If the study confirms the effectiveness of acupuncture treatment, more consistent acupuncture therapy can be set up for clinical practice.

TRIAL REGISTRATION

Chinese Clinical Trials Register identifier, ChiCTR2000031320, registered on 27 March 2020.

Thyroid Hormones and Functional Ovarian Reserve: Systemic vs. Peripheral Dysfunctions

Thyroid hormones (THs) exert pleiotropic effects in different mammalian organs, including gonads. Genetic and non-genetic factors, such as ageing and environmental stressors (e.g., low-iodine intake, exposure to endocrine disruptors, etc.), can alter T4/T3 synthesis by the thyroid. In any case, peripheral T3, controlled by tissue-specific enzymes (deiodinases), receptors and transporters, ensures organ homeostasis. Conflicting reports suggest that both hypothyroidism and hyperthyroidism, assessed by mean of circulating T4, T3 and Thyroid-Stimulating Hormone (TSH), could affect the functionality of the ovarian reserve determining infertility. The relationship between ovarian T3 level and functional ovarian reserve (FOR) is poorly understood despite that the modifications of local T3 metabolism and signalling have been associated with dysfunctions of several organs. Here, we will summarize the current knowledge on the role of TH signalling and its crosstalk with other pathways in controlling the physiological and premature ovarian ageing and, finally, in preserving FOR. We will consider separately the reports describing the effects of circulating and local THs on the ovarian health to elucidate their role in ovarian dysfunctions.

Thyroid and Fertility: Recent Advances

Background: Thyroid disease is prevalent in women of reproductive age, while infertility is common in women with thyroid dysfunction. In this study, we review the recent advances in the field of thyroid and fertility since the publication of the 2017 American Thyroid Association pregnancy guidelines. Summary: Recent studies have confirmed associations of thyrotropin (TSH) elevation and/or thyroid autoimmunity with infertility and low ovarian reserve in subsets of women, and have led to a better understanding of the pathogenesis linking thyroid autoimmunity with infertility. Even though the benefit of treating patients with TSH >4 mIU/L has been confirmed in a large retrospective cohort study, two large randomized controlled trials have failed to show benefit of thyroid hormone on obstetrical outcomes in euthyroid women with thyroid autoimmunity. New data have emerged regarding the potential gonadal toxicity of radioactive iodine (RAI), based on its impact on ovarian reserve and sperm chromosomal abnormalities. Conclusions: There is continued evidence supporting an important role of thyroid hormone in regulation of reproductive tissues at many levels. Recent randomized trials have failed to identify a benefit of thyroid hormone in euthyroid women with thyroid autoimmunity. Further research in the field is needed to more completely delineate the relevant pathways and identify women who may benefit from levothyroxine treatment. The impact of RAI on fertility also merits further investigation.

Effect of melatonin on gonad and thyroid development of offspring of hypothyroid pregnant rats

We investigated the effects of melatonin on rats with induced hypothyroidism during gestation as well as its effect on the development of the gonads of their offspring. Fifteen pregnant rats were divided into three groups: GC, rats without induced hypothyroidism; GH, rats with induced hypothyroidism; GHM, rats with induced hypothyroidism plus melatonin. Hypothyroidism was induced by oral administration of 6-propyl-2-thiouracil and melatonin was applied subcutaneously. Treatments were performed during gestation and lactation. For the matrices, we evaluated the number of pups, body weight gain, ovarian weight, thyroid weight, organosomatic index, thyroid stimulating hormone (TSH) dose and thyroid morphometry. For the pups, weight gain, TSH, weight, morphometry of the gonads and organosomatic index were analyzed, as well as the cell proliferation index. TSH was elevated only in the matrices of GH animals. Melatonin prevented reduction of ovarian and thyroid weight, number of pups, follicular diameter and thyroid epithelial proportion of the matrices with hypothyroidism. The offspring of rats of the GH group exhibited less body weight gain, gonad and thyroid weight, and gonad cell proliferation index compared to the offspring born of rats of the GC and GHM groups. Melatonin prevented the effects of maternal hypothyroidism on the offspring of rats.

Differential expression and immunoreactivity of thyroid hormone transporters MCT8 and OATP1C1 in rat ovary

Thyroid hormones (THs) regulate several physiological processes in female mammals, many of which are related to reproduction such as steroidogenesis in the ovary, oocyte and granulosa cells maturation, follicular development and differentiation, and ovulation. THs actions require the presence of THs transporters to facilitate their cellular uptake and efflux. MCT8 and OATP1C1 are the principal THs transporters. The aim of the present study was to determine the gene expression and cellular localization of MCT8 and OATP1C1 in the rat ovary during the diestrus-II cycle phase. Ovaries of virgin adult rats were histologically processed. Reverse Transcription-PCR and immunohistochemistry analyses for MCT8 and OATP1C1 were done. MCT8 gene expression level was significantly higher (P ≤ 0.01) than that of OATP1C1 in the rat ovary. MCT8 and OATP1C1 were found in all types of ovarian cells but with different immunoreactivity. MCT8 showed stronger immunoreactivity in tertiary and Graafian follicles, corpus luteum and blood vessels, whereas OATP1C1's immunoreactivity was stronger in stroma cells, tunica albuginea, and blood vessels. Our results provide evidence that THs and their transporters are both necessary for ovarian function and that any alteration in these transporters could interfere with reproductive processes such as ovulation and steroidogenesis, compromising fertility.

Overtime trend of thyroid hormones and thyroid autoimmunity and ovarian reserve: a longitudinal population study with a 12-year follow up

BACKGROUND

Ovarian reserve, vital for reproductive function, can be adversely affected by thyroid diseases. Despite alternations of thyroid hormones with ageing, data on interactions between the overtime trend of thyroid functions and ovarian reserve status has rarely been reported. We aimed to examine the overtime trend of thyroid hormones, thyroid peroxidase antibody (TPO Ab) and their associations with ovarian reserve status, identified by levels of age specific anti-mullerian hormone (AMH) in reproductive aged women, who participated in 12-year cohort of Tehran Thyroid Study (TTS).

METHODS

Reproductive age women(n = 775) without any thyroid disease or ovarian dysfunction were selected from the Tehran Thyroid Study cohort. Participants were divided into four age specific AMH quartiles (Q1-Q4), Q1, the lowest and Q4, the highest. AMH was measured at the initiation of study and thyroid stimulating hormone (TSH), free T4 (FT4), and TPO Ab were measured at baseline and at three follow up visits.

RESULTS

At baseline, there was no statistically significant difference in thyroid hormones between women of the four quartiles, although TPO Ab levels were higher in women of Q1. During the follow ups, FT4 was decreased in all quartiles (p < 0.05), whereas TPO Ab increased in Q1 (p = 0.02). Odds ratio of overall TPO Ab positivity in women of Q1 was 2.08 fold higher than those in Q4. (OR: 2.08, 95%CI: 1.16, 3.72; p = 0.01).

CONCLUSION

Women with the lowest ovarian reserves had higher levels of TPO Ab, with a positive trend of this antibody overtime in comparison to other quartiles, indicating that this group may be at a higher risk of hypothyroidism over time.

Thyroid Hormone Deiodination and Action in the Gonads

Alterations in thyroid hormone (TH) status during developmental or adult age are associated with abnormal gonadal development and function in human and animal models. In the developing testis, aberrant levels of TH action lead to disruptions in cell proliferation and differentiation, ultimately influencing testicular size, spermatogenesis, steroidogenesis and male fertility. Recent work is increasingly identifying the systems and signaling pathways in gonadal cells that are affected by TH, as well as delineating the major factors that determine TH signaling in gonadal tissue. The TH receptor alpha, the monocarboxylate transporter 8 and the type 3 deiodinase appear to be major contributors to the timely regulation of TH action in the developing testis.

In vitro fertilization/intracytoplasmic insemination and thyroid function: reviewing the evidence

Recent findings, that specific G protein-coupled TSH receptors (TSHR) and the nuclear thyroid hormone receptors (THRs) are widely expressed in reproductive tissues, reveal the close links between hypothalamus-pituitary-thyroid and hypothalamus-pituitary-gonadal axes. It has been suggested that thyroid function as well as thyroid autoimmunity (TAI) have an impact on Assisted Reproduction Technology (ART) reproductive outcome. Lately, it became evident that ovarian stimulation (OS) may also have an impact on thyroid function. This narrative review describes the mutual interaction between thyroid function and OS, by reviewing the current evidence, assessing the pathophysiological links and arriving at practical recommendations.