A comparison between enalapril and captopril on insulin sensitivity in normotensive healthy volunteers

Captopril has been shown to improve insulin sensitivity in insulin resistant hypertensive individuals and enalapril has been shown to improve insulin sensitivity in a small group of healthy volunteers, but there has been no direct comparison of the effects of the different angiotensin converting enzyme inhibitors (ACEIs) on insulin sensitivity in either insulin sensitive or insulin insensitive populations.

To compare the impact of two different ACEIs (captopril and enalapril) on insulin mediated glucose uptake in normotensive, non-obese, insulin sensitive subjects.

A single blind cross-over study comparing captopril (6.25 mg twice daily) and enalapril (5 mg once daily) for 28 days with a 28 day washout period between drugs. Insulin mediated glucose uptake was measured by means of the euglycaemic hyperinsulinaemic clamp at the start and completion of each period of drug therapy.

Both drugs resulted in elevations of fasting insulin levels (mean difference +/- SEM for combined data, 2.7 +/- 1.8; p < 0.05) and a reduction in insulin mediated glucose uptake (mean difference for combined data, -0.72 +/- 0.37 mg/kg-1 minute-1; p = 0.056). Results were similar for both agents and suggest a class effect.

The increase in fasting insulin levels, and reduction in insulin mediated glucose uptake in this study are in contrast to findings in obese and hypertensive subjects, and indicate that studies of insulin sensitivity of ACEIs in non-obese, normotensive subjects are inappropriate for predicting likely effects in clinical practice.