Changes in Ovarian Function Induced by Letrozole in an Endometriosis Rat Model

OBJECTIVE: To investigate changes in ovarian function induced by letrozole in a rat model of endometriosis. STUDY DESIGN: Endometriosis was surgically induced in 36 Sprague-Dawley Twelve rats served as controls and received 1 mL normal saline daily orally. Twelve rats in the low-dose letrozole group received 0.2 mg/kg/day of oral letrozole. Another 12 rats in the high-dose letrozole group were administered 0.5 mg/kg/day of oral letrozole. Daily vaginal smears were obtained to observe rats' estrous cycles. The serum levels of sex hormones were assayed using chemiluminescence method. Histological examination of endometriotic tissues and ovaries was carried out using hematoxylin and eosin staining. RESULTS: The rats lost regular estrous cycles after 2 weeks of letrozole treatment and had significantly higher levels of follicle-stimulating hormone, luteinizing hormone, and testosterone, while levels of estradiol and progesterone were significantly lower. Ovaries in the letrozole groups showed several follicles with cystic dilation and without signs of ovulation. The mean areas and histological scores of the implants in the letrozole groups were lower after treatment. CONCLUSION: Letrozole treatment induced a polycystic ovary-like syndrome in the rat endometriosis model. Decreased sizes and lower histological scores of endometriotic implants were also observed in the letrozole-treated rats.