Evoluation of effect of experimental hypothyroidism on ovarian follicles

Hypothyroidism is a condition caused by the insufficient production of thyroid hormones (T4 and T3), leading to the slowing down of bodily functions. It can affect reproductive health by disrupting the menstrual cycle and fertility, and may result in recurrent pregnancy losses. Animal studies have shown that hypothyroidism inhibits follicular maturation and impairs ovarian function. Epidermal growth factor (EGF) is a polypeptide that plays a crucial role in cell growth and differentiation, while the EGF receptor (EGFR) is the receptor to which EGF binds. Thyroid hormones can influence EGF and EGFR levels, and hypothyroidism may lead to a reduction in EGFR levels. EGF supports the growth of granulosa cells and follicular development, and is essential for oocyte maturation and ovulation. The aim of this study is to investigate the effects of induced hypothyroidism on ovarian follicles and the impact of EGFR in hypothyroid- induced ovarian follicles in adult rats. In this study, 18 female Wistar rats were used. Ten rats, randomly selected, were assigned to the hypothyroidism group, receiving 10 mg/kg of methimazole in their drinking water for 30 days, while the remaining 8 rats constituted the control group. The effects of methimazole on the rats were evaluated biochemically in blood serum, histologically in ovarian tissue, and through immünohistochemical and GZ-PZR analyses. A decrease in serum T3 levels was observed in the hypothyroidism group. Significant reductions in the average body and ovarian weights, as well as in the number of primary, secondary, and tertiary follicles, were detected in the hypothyroidism group rats. Immunohistochemical analysis also revealed a decrease in EGFR expression in the hypothyroidism group. GZ-PZR analysis showed that while HB-EGF, EGFR, GPER1, and ESR1 gene expressions increased in the hypothyroidism group compared to the control group, RAF1 expression decreased. Methimazole leads to significant impairments in ovarian follicular development and oocyte quality in rats.