Sex-Dependent Effect of Metformin on Serum Prolactin Levels In Hyperprolactinemic Patients With Type 2 Diabetes: A Pilot Study

Background Metformin was found to reduce circulating levels of pituitary hormones. Objective The purpose of this study was to assess whether sex determines the effect of metformin on lactotroph secretory function. Methods The study population included 25 women and 12 men with mildly elevated serum prolactin levels (25-75 ng/mL). Because of concomitant type 2 diabetes, all participants were treated with metformin (3 g daily). Plasma levels of glucose and lipids, HOMA1-IR, serum levels of prolactin, thyrotropin and free thyroid hormones, as well as Jostel's, SPINA-GT and SPINA-GD indices were assessed at baseline and at the end of metformin treatment. Results The study completed 24 women and 11 men. At baseline, there were no significant differences in circulating levels of glucose and lipids, insulin sensitivity, hormones, Jostel's, SPINA-GT and SPINA-GD indices between women and men. In both men and women, metformin reduced fasting glucose levels and HOMA1-IR. However, only in women metformin decreased elevated prolactin levels and this effect correlated with an improvement insulin sensitivity, as well as with the impact on SPINA-GT. Conclusions The results of the study suggest that the effect of metformin on serum prolactin levels is sex-dependent.