Melatonin causes regression of endometriotic implants in rats by modulating angiogenesis, tissue levels of antioxidants and matrix metalloproteinases.

Purpose: The aim of this study was to test if melatonin causes regression of endometriotic implants and whether it influences implant levels of superoxide dismutase (SOD), malondialdehyde (MDA), vascular endothelial growth factor (VEGF), tissue inhibitor of metalloproteinase (TIMP)-2 and matrix metalloproteinase (MMP)-9 in rats.

Methods: Endometriotic implants were introduced surgically to 20 female Wistar albino rats, which were either treated with melatonin via intraperitoneal injection for four weeks (melatonin group, n = 10) or with saline (control group, n = 10) after a second-look laparotomies. The main outcome measures included volume (mm(3)) and weight (mg) of explants and tissue levels of SOD, MDA, VEGF, TIMP-2 and MMP-9.

Results: Before and after treatment implant volumes of the melatonin group were decreased significantly (P < 0.01) while there was no significant difference between the pretreatment and posttreatment implant volumes of the control group. Moreover, weight (P < 0.05) and histologic score (P < 0.05) of implants of the melatonin-treated rats were significantly lower than controls. Activity of SOD and TIMP-2 staining in melatonin group was significantly higher (both P < 0.01) while there were significant reductions in implant levels of VEGF and MMP-9 in melatonin group (both P < 0.01) than controls.

Conclusions: Melatonin induces the regression of endometriotic implants in rats by modulating implant levels of SOD, MDA, VEGF, MMP-9 and TIMP-2.