Effect of experimental hyperthyroidism on ovarian tissue

Objective: Thyroid hormones are endocrine factors that play an important role in regulating reproductive functions. This study aimed to investigate the molecular and histological effects of experimentally induced hyperthyroidism on rat ovarian tissue. Materials and Methods: Three groups of female rats (control, sham, and hyperthyroid; nine rats per group) were used. Hyperthyroidism was induced by administering levothyroxine for seven days. At the end of the experiment, serum and ovarian tissues were collected. AMH, FSHR, and leptin levels were evaluated in tissue using the ELISA method. The expression levels of these genes in ovarian tissues were analyzed by RT-qPCR, and protein levels were assessed by ELISA. In addition, follicle counting was performed in histological sections, and ovarian morphology was examined. Results: In the hyperthyroid group, prominent fibrosis in the ovarian stroma and thickening of the tunica albuginea were observed. A decrease in follicle count, particularly in preantral and antral follicles, was detected. Molecular analyses revealed decreased expression of AMH and leptin genes, whereas FSHR expression increased compared to the control group. Tissue protein levels showed a distribution consistent with gene expression patterns. Conclusion: Experimental hyperthyroidism causes significant morphological and molecular alterations in rat ovaries. The increase in thyroid hormones may negatively affect fertility by disrupting the expression of factors related to folliculogenesis and ovarian reserve. Keywords: Hyperthyroidism, ovary, infertility, folliculogenesis, perioovarian adipose tissue