How much total ovarian tissue can be removed without compromising ovarian function? An animal study

Objective: Removal of ovarian tissue is a new option for fertility preservation for certain cancer patients in China. The aim was to investigate the impact of stepwise removed tissue on hormone levels and follicles in rats. Methods: Six to ten-week old rats were divided into six groups (% total ovarian tissue): 1 = control (100%), 2 (75%), 3 (50%), 4 (25%), 5 (12.5%), 6 (0%, bilateral ovariectomy). Blood test was carried out fortnightly to assess estradiol (E2), progesterone (P), follicle-stimulating hormone (FSH), anti-Mullerian hormone (AMH), and inhibin B (INHB). Ovaries are obtained from surgical resections and from rats sacrificed after 12 weeks. Results: During 12 weeks, groups 4, 5, and 6 had higher FSH and lower AMH and INHB values compared to control (p< .05), but in group 4 E2 and P was not significantly different from control (p> .05). All ovarian function parameters stopped in groups 5 and 6. Follicle morphology was not significantly different between baseline and 12 weeks after surgery in groups 1-5. Conclusions: For the first time, we demonstrated that even up to 75% of total ovarian tissue can be removed without impact on E2 and P production in rats, which, if confirmed in women, would mean that hazardous (or possibly contraindicated in cancer patients) hormone therapy is not required to avoid the negative consequences of hormone depletion.