Metformin increases urinary sodium excretion by reducing phosphorylation of the sodium-chloride cotransporter.

OBJECTIVE: Metformin is an antidiabetic drug that is widely used to treat patients with diabetes mellitus. Recent studies have reported that treatment with metformin not only improved blood glucose levels but also reduced blood pressure. However, it remains unclear how metformin reduces blood pressure. We hypothesized that metformin affects sodium reabsorption in the kidneys. METHODS: Urinary sodium excretion and expression of renal sodium transporters were examined in 8-week-old male C57BL/6 mice with acute and chronic treatment of metformin. In addition, we examined metformin effects using ex vivo preparations of mice kidney slices. RESULTS: In this study, we demonstrated that metformin increased urinary sodium excretion by reducing phosphorylation of the thiazide-sensitive Na-Cl cotransporter (NCC) in acute and chronic metformin administration. We also confirmed reduction of phosphorylated NCC in an ex vivo study. The activity of other renal sodium transporters, such as NKCC2, ENaC, and NHE3 did not show significant changes. WNK-OSR1/SPAK kinase signals were not involved in this inactivation effect of metformin on NCC. CONCLUSION: Metformin increased urinary sodium excretion by reducing phosphorylation of NCC, suggesting its role in improving hypertension.