How much total ovarian tissue can be removed without compromising ovarian function? An animal study
KEYWORDS 2 ovariectomy, ovarian function, ovarian tissue cryopreservation, premature ovarian insufficiency, fertility protection 3 Abstract Purpose Until now, it is not clear how much total ovarian tissue can be removed without affecting ovarian functions. Aim to investigate impact of stepwise removed ovarian tissue on endocrine hormone levels reflecting ovarian function, follicle morphology and weight in rats. Methods The study was performed with six groups of animals, each consisting of six
... consisting of six ten-week-old Sprague-Dawley rats. A blood test was performed on the day of surgery (baseline) and fortnightly thereafter to assess serum hormones reflecting ovarian function: estradiol (E2), progesterone (P), follicle-stimulating hormone (FSH), anti-Müllerian hormone (AMH), inhibin B (INHB); weight was also assessed. The ovaries obtained from surgical resection and from the rats sacrificed 12 weeks after surgery were stained with hematoxylin-eosin. Surgeries in the groups; [%] of remaining total ovarian tissue: Group 1, non-ovariectomized [100% tissue]. Group 2, half of left ovary excised [75% tissue]. Group 3, left ovary excised [50% tissue]. Group 4, left ovary + half of right ovary excised [25% tissue]. Group 5, left ovary + three quarters of right ovary excised [12.5% tissue]. Group 6, bilateral ovariectomy [0% tissue]. Results During the 12 weeks, group 4, 5 and 6 had higher FSH and lower AMH and INHB values compared to the control (group 1) ( p <0.05), but in group 4 production of E2 and P was not significantly different from control ( p >0.05). All ovarian function parameters completely stopped in group 5, i.e. the same as the bilateral ovariectomized rats (group 6). Weight significantly increased in group 6 ( p <0.05). Follicle morphology at baseline and 12 weeks after surgery in groups 2-5 was not significantly different to the control. Conclusions Our animal study confirms that removal of one ovary maintains the remaining ovarian tissue's potency for normal hormone production, as already suggested in clinical studies. However, to our knowledge, we demonstrate here for the first time that even up to 75% of total ovarian tissue can be removed without impact on E2 and P production, which if confirmed in women would mean that hazardous hormone replacement therapy is not required to avoid the negative consequences of hormone depletion.