After administering metformin to STZ-induced diabetic rats and to pancreatic β cells (INS-1 cells) that had been harmed by hyperglycemia and hyperlipidemia, it was found that metformin can reverse the downregulation of AQP7 expression in islet cells caused by diabetes, and then promote an increase in glycerol entry into the pancreas and subsequent insulin secretion. The gene discussed is AQP7; the disease is diabetes mellitus.