Background: Patients with non-insulin-dependent diabetes mellitus (NIDDM) exhibit poor clinical outcomes from myocardial ischemia. This may reflect an impairment in their cardiac insulin-response system.
Methods and results: We used AV balance and intracoronary infusion techniques to compare the intrinsic cardiac responsiveness to insulin in 26 coronary disease patients with (n=13) and without (n=13) NIDDM. During fasting, NIDDM hearts demonstrated lower fractional extraction of glucose from arterial plasma than controls (1.0+/-0.5% versus 2.1+/-0.5%, P<0.05) despite higher circulating insulin levels (26+/-5 versus 13+/-4 microU. mL, P<0.05). This was compensated for by higher circulating glucose levels, so that net cardiac glucose uptake in the 2 groups was equivalent (5.2+/-1.1 versus 5.3+/-1.1 micromol. min). Intracoronary insulin infusion produced an approximately 3-fold increase in fractional extraction and net uptake of glucose across the heart in both groups (to 3.7+/-0.4% and 18.3+/-3.5 micromol. min in NIDDM and to 5.4+/-0.7% and 17.7+/-4.3 micromol. min in controls) accompanied by an approximately 30% increase in net lactate uptake, suggesting preserved insulin action on both glucose uptake and glucose oxidation in the NIDDM heart. In nondiabetics, insulin consistently increased coronary blood flow, but this effect was absent in NIDDM.
Conclusions: In contrast to their peripheral tissues and coronary vasculature, the myocardium of patients with NIDDM expresses a competent insulin-response system with respect to glucose metabolism. This suggests that insulin resistance is mediated at the level of individual organs and that different mechanisms are involved in muscle and vascular tissue.