ANGIOTENSIN-CONVERTING ENZYME-INHIBITORS AND INSULIN SENSITIVITY - METABOLIC EFFECTS IN HYPERTENSION, DIABETES, AND HEART-FAILURE

Angiotensin-converting enzyme (ACE) inhibitors are established in the treatment of hypertension and heart failure; both conditions are complicated by resistance to insulin-mediated glucose disposal. The defect in essential hypertension is both tissue and pathway specific, i.e., confined to nonoxidative (glycogen synthetic) routes of intracellular glucose utilization in skeletal muscle, whereas heart failure and non-insulin-dependent diabetes mellitus (NIDDM) are associated with more widespread abnormalities of carbohydrate and lipid metabolism. Thus, the mechanisms of the insulin resistance in hypertension, NIDDM, and heart failure are fundamentally different, so metabolic responses to drug therapy may not be the same in all insulin-resistant states. There have been conflicting reports about the effects of ACE inhibitors on insulin sensitivity and glycemic control. A number of studies, both with captopril and with enalapril, have shown small increases in insulin sensitivity, and there is evidence that this is due to enhanced glucose uptake into skeletal muscle. The interpretation of these studies, however, is often compromised by poor trial design, lack of full placebo data, various indirect measurements of insulin sensitivity. and heterogeneous patient populations in whom the biochemical mechanisms of insulin resistance (and drug responses) may not be the same. Overall, there probably is a modest class effect of ACE inhibitors that enhances insulin-mediated glucose disposal; the mechanism of this effect is likely to be a combination of increased muscle blood flow. local renin-angiotensin system blockade, and elevated kinin levels.