Effects of raloxifene on insulin sensitivity, β-cell function, and hepatic insulin extraction in normal postmenopausal women

Objective: To investigate the effect of raloxifene on insulin sensitivity, β-cell function, hepatic insulin clearance, and glucose tolerance in postmenopausal women. Design: Prospective study. Setting: University of Texas Medical Branch at Galveston, Texas. Patient(s): Twenty normal postmenopausal women. Intervention(s): An oral glucose tolerance test (OGTT) was performed on all study participants before and after treatment with 60 mg of raloxifene daily for 3 months. Blood samples were obtained at baseline and 1, 2, and 3 hours after 75-g oral glucose administration for measurement of glucose, insulin, proinsulin, and c-peptide levels. Insulin tolerance test (ITT) and euglycemic clamp studies were also performed before and after treatment. Main Outcome Measure(s): Glucose and insulin area under curve (AUC) were calculated. The c-peptide to insulin ratio was determined to assess hepatic clearance of insulin. The homeostasis model assessment (HOMA) was used to calculate the index of insulin resistance (HOMA-IR) and β-cell function (HOMA-%β). Insulin sensitivity was assessed by insulin tolerance test and glucose infusion rate (GIR) during euglycemic clamp studies. Result(s): There was no change in fasting or AUC glucose levels. Fasting insulin levels were not statistically significantly different, but the insulin levels at 2 hours and insulin AUC were higher after treatment compared with before treatment. Proinsulin, c-peptide levels, and HOMA-%β did not change. The c-peptide to insulin molar ratio was statistically significantly decreased after treatment. There was no change in insulin sensitivity. Conclusion(s): These results indicate that raloxifene has no adverse effect on insulin sensitivity or glucose tolerance, and it does not affect β-cell function. After glucose load, raloxifene decreases hepatic insulin extraction and thus conserves insulin, which may be beneficial to patients with decreased β-cell reserve or those predisposed to type 2 diabetes.