Introduction: Among the endocrine diseases, hypothyroidism is the commonest after diabetes.Thyroid hormones (T3,T4) are essential for genital organs function. Apoptosis process in ovarian cells plays a significant role of development in ovarian follicles. The aim of the present study was determine the apoptotic index induced by hypothyroidism in rat ovarian follicles.

Materials and Methods: In the present study, twenty female mature wistar rats were used with age of 2.5 months and weight of 200-250 (g). Rats were divided into test and control groups. In test group chemical hypothyroidism induced by propylthiouracil (PTU500 mg/L) in drinking water. The control group only received normal drinking water. After three weeks the rats were killed and their ovaries removed and were fixed for tissue preparation. TUNEL technique were used for determine of apoptosis. Cells count done by stereological method. Data were analyzed by t-test and one-way ANOVA followed by Tukey test. Significance was accepted at P<0.05.

Results: The findings showed that the apoptotic index had a significant decrease in late antral and graffian follicles (P=0.000) and no significant decrease in preantral and early antral follicles (P>0.05) in hypothyroid group. All granulosa cells were TUNEL-positive in primary follicles but no cell was seen in primordial follicles in groups.

Conclusion: The results of the present study showed that the hypothyroidism may be vigorous decreased of apoptotic index in antral and graffian follicles. Hypothyroidism increased the number of luteal bodies and decreased the number of graffian follicles in ovarian tissue.