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 hyperinsuline-miceuglycemic clamp(HE)(n=10; 40±9 years, 8 female subjects, hemoglobin A1c HbA1c 7.8±1.1%) or hyperinsulinemic-hyperglycemic clamp(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. 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 hyperinsuline-miceuglycemic clamp (HE) (n = 10; 40 ± 9 years, 8 female subjects, hemoglobin A1c HbA1c 7.8 ± 1.1%) or hyperinsulinemic-hyperglycemic clamp , 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), it didnt change in the HE group. Compared with baselin e 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). 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.