Hassan Malekinejad - Department of Pharmacology & Toxicology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran
Mahdi Hamidi - Department of Pharmacology & Toxicology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran
Rajab-Ali Sadrkhanloo - Department of Histology and Embryology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran
Abbas Ahmadi - Department of Histology and Embryology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran

Objective(s) The effect of tamoxifen as a selective estrogen receptor modulator which is widely used for treatment of early and metastatic breast cancer was investigated on the folliculogenesis in rat's fetuses and neonates. Materials and Methods The pregnant rats assigned into test and control groups. Control group received olive oil and treatment groups received either ۱۷-β-estradiol (۱۰ µg/kg/day) or tamoxifen (۰.۴ mg/kg/day) between days ۸-۱۳ of pregnancy. On day ۲۰th of pregnancy the rats euthanized and the blood samples were collected for determination of FSH, E۲, and the fetuses fixed for histological studies. Another group of pregnant rats went forward to obtain their neonates and we euthanized the neonates and the genital system was collected for further histopathological analyses on day ۵th. Results The histological examinations of the fetus’s and neonate's ovaries and biochemical data showed significant changes in the rats which treated with tamoxifen. The absence of folliculogenesis and an increase in E۲ level in tamoxifen-treated group which accompanied with sharp decrease of FSH level in comparison with the control group were demonstrated. By contrary, E۲ treated group showed a positive progress in development in terms of the formation of secondary follicles and also supportive connective tissues in comparison with the control group. Conclusion This  study  supports  the  previous  findings  showing  that  tamoxifen  has  effects  on  the development of ovaries and therefore, it should be avoided or used with great caution in pregnant women.

۱۷- β-estradiol, Folliculogenesis, FSH, Ovary, Tamoxifen