The effects of metformin and letrozole on endometriosis and comparison of the two treatment agents in a rat model.

BACKGROUND Our aim was to investigate the effects of metformin and letrozole on experimentally induced endometriosis in a rat model. METHODS Endometriotic implants were surgically formed, and 38 rats were randomly divided into four groups. Group 1 (control group, 8 rats) was given no medication. Group 2 (metformin group, 10 rats) was given 100 mg/kg/day of oral metformin. Group 3 (metformin group, 10 rats) was given 200 mg/kg/day of oral metformin. Group 4 (letrozole group, 10 rats) was given 0.1 mg/kg/day of oral letrozole. All rats continued to receive the treatment for 4 weeks and then were sacrificed to assess the size of implants and scores of adhesions. The histopathologic scores of implants in excised endometriotic foci were examined by a pathologist. RESULTS The mean surface area of endometriotic implants was similar in all groups before the treatment. Although the area was not reduced in controls, it was found to be significantly reduced in all treatment groups (44.50 +/- 23.37, 5.90 +/- 2.37, 4.30 +/- 1.33, 6.90 +/- 3.72 mm(2), respectively; P < 0.05). The effect was comparable between the treatment groups. The histopathologic assessment revealed that the histopathologic score of implants was lowest after 100 mg/kg/day metformin. Additionally, metformin reduced the severity of adhesions. CONCLUSIONS Metformin and letrozole caused a statistically significant regression of endometriotic implants. The effects of metformin on endometriotic tissue were at least comparable to letrozole.