Effects of melatonin and metformin on the ovaries of rats with polycystic ovary syndrome

Objective To study the combined and isolated effects of melatonin and metformin in ovarian tissue of PCOS rats. Design Forty adult female rats were divided into five groups: physiological estrus phase (Sham); permanent estrus with PCOS induced by continuous lighting exposure for 60 consecutive days (Control); with PCOS treated with melatonin; with PCOS treated with metformin; with PCOS treated with melatonin+metformin. After 60 days of treatments, all rats were euthanized and ovaries were collected and processed for paraffin-embedding. Formalin-fixed paraffin-embedded sections were stained with hematoxylin/eosin, or subjected to immunohistochemistry for proliferation (Ki-67) and apoptosis (cleaved-caspase 3) detection markers. Results Absence of corpus luteum, higher number of cysts, and increased nuclear volume and area of interstitial cells, along with decreased in primary and antral follicles number, were noticed in the control group than in the Sham group. Melatonin and metformin treatments attenuated these effects, although the combined treatment did not mitigate the increased number of cysts/ovary induced by PCOS. An increase in theca interna cells apoptosis was observed in the control group, while melatonin and metformin treatments reduced it significantly. A higher percentage of Caspase-3-immunostained granulosa cells was noted in the SHAM and all treated groups as compared to control group; no additive effects in ovarian cells apoptosis were observed in the combined treatment. The percentage of Ki-67-immunostained granulosa cells was significantly higher in the control group as compared to the Sham group. However, the combined treatment but not melatonin and metformin alone mitigated this effect. A higher percentage of Ki-67-immunostained interstitial cells was observed in all treated groups, as compared to Sham and control groups, whereas no additive effects in that immunoreactivity were observed in the combined treatment. Conclusions Melatonin and metformin may improve ovarian function in PCOS rats. The combined melatonin/metformin treatment is more effective in attenuating excessive granulosa cell proliferation, but it is not more effective in improving ovarian function than these drugs applied alone in PCOS rats.