Thyroid hormones (TH) play a critical role in ovarian follicular development, maturation and the maintenance of various endocrine functions. However, whether TH can affect ovarian follicular development in neonatal and immature rats remains unclear. Therefore, the aim of the present study was to elucidate the effect of TH on ovarian follicular development in neonatal and immature rats. Thirty female post-lactation mothers of Sprague-Dawley rat pups were randomly divided into three groups: control, hyperthyroid (hyper), and hypothyroid (hypo). On postnatal days (PND) 10 and 21, body weights, serum hormones, ovarian histologic changes, and immunohistochemistry of thyroid hormone receptor alpha 1 (TRα1) and nitric oxide synthase types (NOS), and NOS activities, were determined. The data showed that body weights significantly decreased in both hyper and hypo groups compared with the control group (P < 0.05). In addition, the hyper group had increased serum concentrations of T3, T4, and E2; whereas the hypo group manifested reduced serum concentrations of T3, T4, and E2 on PND 10 and 21. The hyper and hypo groups showed significantly reduced total number of primordial, primary and secondary follicles on PND 10 and 21 compared with the control group (P < 0.05). Similarly, antral follicle numbers in the hyper and hypo groups were significantly decreased on PND 21 compared with the control group (P < 0.05). Immunostaining indicated that TRα1 and NOS were expressed in ovarian surface epithelium and oocytes of growing and antral follicles, with strong staining of the granulosa and theca cells of follicles. NOS activities were significantly augmented in the hyper, but diminished in the hypo groups on PND 10 and 21. In summary, our findings suggest that TH play important roles in ovarian functions and in the regulation of NOS activity. Our results also indicate that a relationship exists between the TH and NO signaling pathways during the process of ovarian follicular development in neonatal and immature rats.

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Thyroid hormones and oxidative stress play significant roles in the normal functioning of the female reproductive system. Nitric oxide (NO), a free radical synthesized by nitric oxide synthases (NOS), participates in the regulation of thyroid function and is also a good biomarker for assessment of the oxidative stress status. Therefore, the purpose of this study was to investigate effects of thyroid hormones on uterine antioxidative status in young adult rats. Thirty immature female Sprague-Dawley rats were randomly divided into three groups: control, hypothyroid (hypo-T) and hyperthyroid (hyper-T). The results showed the body weights decreased significantly in both the hypo-T and hyper-T groups and that uterine weights were decreased significantly in the hypo-T group. The serum concentrations of total triiodothyronine (T3) and thyroxine (T4), as well as estradiol (E2), were significantly decreased in the hypo-T group, but increased in the hyper-T group. The progesterone (P4) concentrations in the hypo- and hyperthyroid rats markedly decreased. Immunohistochemistry results provided evidence that thyroid hormone nuclear receptor α/β (TRα/β) and three NOS isoforms were located in different cell types of rat uteri. The NO content and total NOS and inducible NOS (iNOS) activities were markedly diminished in the hypo-T group but increased in the hyper-T group. Moreover, the activities of both glutathione peroxidase (GSH-Px) and catalase (CAT) exhibited significant decreases and increases in the hypo-T and hyper-T groups, respectively. The malondialdehyde (MDA) contents in both the hypo-T and hyper-T groups showed a significant increase. Total superoxide dismutase (T-SOD) activity in the hypo- and hyper-T rats markedly decreased. In conclusion, these results indicated that thyroid hormones have an important influence on the modulation of uterine antioxidative status.

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To expand our understanding of the roles of thyroid hormones on female reproduction, we induced hypo- and hyper-T rat models to investigate the roles of thyroid hormones on estrous cyclicity, as well as the antioxidative status in the ovaries of rats. In the current study, our data show that hypothyroidism (hypo-T) and hyperthyroidism (hyper-T) led to significantly reduced body weights and ovarain weights and delayed vaginal opening day. For hyper-T, thyroxine (T4), tri-iodothyronine (T3), progesterone (P4) and follicle-stimulating hormone (FSH) were significantly increased, while estradiol (E2) and luteinizing hormone (LH) were significantly decreased. For hypo-T rats, serum levels of total T4 and T3, E2, P4, FSH and LH were significantly increased, while concentrations of E2 and LH were significantly decreased. For ovary morphology, the numbers of secondary and antral follicles were significantly decreased with more atretic antral follicles and less corpora lutea in both hyper- and hypo-T groups. Both hyper-T and hypo-T treatment significantly decreased the expressions of thyroid hormone receptor α1 in the ovary. Hypo-T significantly reduced nitric oxide (NO), total NO synthase (tNOS), inducible NOS and constitutive NOS activities, but hyper-T increased them. For antioxidative parameters, hypo-T and hyper-T treatment significantly increased malondialdehyde (MDA) contents. The activities of both glutathione peroxidase (GSH-Px) and catalase (CAT) significantly decreased in the hypo-T group but increased in the hyper-T group. Total superoxide dismutase (T-SOD) activity was significantly increased in the hyper-T group. In summary, thyroid hormones alter estrous cyclicity and antioxidative status in the ovary of the rat may act through the NOS signaling pathway.

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Thyroid hormones are important in the development and regulation of testes. This study was conducted to determine the effects of hyper- and hypothyroidism on testicular development in prepubertal rats aged 20-70 days. Weaning male rats (20 days old) until day 70 age were randomly divided into four groups: control, hyperthyroid (hyper-T), hypothyroid (hypo-T) and hypothyroid treated with thyroxine (T4) (hypo-T+T4). The results indicated that thyroid hormones caused a significant effect in body and testis weights, and food and water consumption. In addition there were changes in serum concentrations of tri-iodothyronine, T4, thyroid stimulating hormone (TSH) and testosterone. Histomorphology showed a significant decrease in seminiferous tubule diameter in hyper-T compared to the other groups. Leydig cell numbers showed a significant elevation in hyper-T but not in hypo-T groups. Immunostaining indicated that TSH receptor (TSHR), thyroid hormone receptors α/β (TRαβ) and proliferating cell nuclear antigen (PCNA) have the roles in testicular development. Our findings suggest that hyper- and hypo-thyroidism regulate testicular cell proliferation and spermatogenesis in prepubertal rats, indicating that expression of TSHR, TRαβ and PCNA may be regulated by thyroid hormones that are involved in testicular development; and that the administration of T4 to the hypo-T+T4 group leads to an improvement in the testicular condition.