The effects of plasma insulin and glucose on myocardial blood flow in patients with type 1 diabetes mellitus

OBJECTIVES The objective of this study was to determine the impact of insulin and glucose on myocardial vasodilator function in patients with type 1 diabetes mellitus (T1DM). BACKGROUND The relative importance of plasma insulin and glucose levels on the abnormal vasodilator function observed in T1DM is unknown. METHODS Twenty T1DM patients underwent positron emission tomography studies to measure myocardial blood flow (MBF) (in ml/g/min) at rest (MBFr) and during adenosine (MBFa), both under baseline metabolic conditions and then during either hyperinsulinemic-euglycemic clamp (HE) (n = 10; 40 +/- 9 years, 8 female subjects, hemoglobin A1c [HbA1c] 7.8 +/- 1.1%) or hyperinsulinemic-hyperglycemic damp (HH) (n = 10; 44 +/- 12 years, 8 female subjects, hemoglobin A1c 7.7 +/- 0.6%). RESULTS Both groups showed similar MBFr and MBFa under baseline metabolic conditions (p = NS). Compared with baseline conditions, MBFr increased in the HH group (p < 0.005), whereas it did not change in the HE group. Compared with baseline conditions, MBFa decreased in the HH group (p < 0.05) but did not change in the HE group. Myocardial perfusion reserve (MPR) (MBFa/MBFr) was similar between the HE and HH groups at baseline (p = NS). During clamp, MPR tended to decrease in the HH group (p < 0.1) but did not change in the HE group (p = NS) when compared with baseline conditions. However, during the clamp MPR was significantly lower in the HH group when compared with the HE group (p < 0.0001). CONCLUSIONS In the short term, hyperglycemia has a deleterious effect on myocardial vasodilator function, which outweighs the beneficial effect of hyperinsulinemia. (J Am Coll Cardiol 2005;46: 42-8) (c) 2005 by the American College of Cardiology Foundation.