Differential effect of chronic treatment with two beta-blocking agents on insulin sensitivity

Background Hypertensive patients frequently show resistance to insulin-stimulated glucose uptake and hyperinsulinemia. Diuretics and β-adrenoceptor blocking agents have been found to decrease insulin sensitivity, whereas α1-blockers and angiotensin converting enzyme inhibitors seem to improve it. Objective To compare the effects of a 3 months' antihypertensive treatment with carvedilol, a non-selective β-adrenoceptor blocker with α1-blocking properties, with the β1-selective receptor blocker metoprolol on insulin sensitivity in non-diabetic hypertensive patients. Design A multicenter double-blind randomized study. Subjects and methods Seventy-two non-diabetic hypertensive patients were randomly assigned to treatment with either carvedilol or metoprolol. An isoglycemic, hyperinsulinemic glucose clamp was conducted before and after 12 weeks of treatment; the metabolic clearance rate for glucose was taken as an indicator of insulin sensitivity. Results The two groups did not differ in age, sex, body mass index, blood pressure or lipids, and treatment effectively lowered blood pressure. In both groups, insulin sensitivity was impaired at baseline. After metoprolol treatment, insulin sensitivity further decreased significantly by about 14%, whereas it increased after carvedilol. There was also a decrease in high-density lipoprotein and an increase in triglycerides levels in patients in the metoprolol-treated group, whereas these parameters remained unchanged in patients in the carvedilol-treated group. Conclusion This study confirms previous findings of a reduction in insulin sensitivity after chronic metoprolol treatment. Carvedilol treatment, however, resulted in a slight increase in insulin resistance and a better lipid profile. We thus demonstrate that a β-blocker with α1-blocking properties has favorable effects on glucose metabolism, suggesting a potentially important role of peripheral blood flow in regulating glucose uptake. These findings imply that β-blocker treatment, when combined with α1-blocking activity has advantageous effects on insulin sensitivity and lipids and could therefore be suitable for patients with the metabolic syndrome.