Thyroid gland dysfunction modulates ovarian response to estrogen and androgen receptors in albino rats

Abstract

The Egyptian Journal of Histology 2011, 34:182–190 17 (1254 -2011) Background Hypothyroidism and hyperthyroidism are more common in women than in men, and it was reported that thyroid hormones play an essential role in ovarian physiology. Aim This study aimed to simulate the clinical conditions of hypothyroidism and hyperthyroidism in adult female albino rats, and to detect the possible changes in ovarian estrogen and androgen hormone receptors associated with such clinical conditions. Materials and methods This study used 36 adult female albino rats. Rats were divided into three groups, with 12 rats each. Rats of the control group received 0.5 ml saline (0.9%) solution once daily. Six rats received the saline orally using a tube, and the other half received it by intraperitoneal injection for 4 weeks. The rats of the hypothyroid group received daily orally a dose of 18.75 mg/kg propylthiouracil dissolved in saline solution for 4 weeks, and the rats of the hyperthyroid group received a daily intraperitoneal dose of 40 mg/kg L-thyroxine dissolved in saline solution for 4 weeks. Vaginal smears were performed at the end of the experiment; only 22 rats coincided the diestrus phase of the cycle, sacrificed and sections were subjected to hematoxylin and eosin and immunohistochemical staining for estrogen and androgen receptors. Results In the hypothyroid group, few corpora lutea, atretic follicles, and dilated congested blood vessels were clearly seen. In the hyperthyroid group, the ovarian sections showed numerous corpora lutea; atretic follicles and markedly dilated congested blood vessels were also noted. A negative correlation was documented between estrogen receptor and androgen receptor immunoreactivity in the hypothyroid and hyperthyroid groups. Conclusion This study suggested that thyroid hormones are important to maintain a normal estrous cycle and hence in the regulation of ovarian hormones. The mechanisms by which thyroid hormones influence ovarian function remain to be elucidated. However, it might be through their effect on the aromatase enzyme, which is the key regulator in ovarian hormones production reflected on the level of steroid hormones receptor expression.