Endothelial and metabolic characteristics of patients with angin and angiographically normal coronary arteries : Comparison with subjects with insulin resistance syndrome and normal controls

OBJECTIVES This study was performed to characterize the endothelial and metabolic alterations of patients with angin and angiographically normal coronary arteries (“cardiac” syndrome X [CSX]) compared with subjects with insulin resistance syndrome (“metabolic” syndrome X [MSX]) and normal controls. BACKGROUND Previous studies have found high endothelin-1 levels, impaired endothelium-dependent vasodilation and insulin resistance in patients with angin pectoris and angiographically normal coronary arteries. On the other hand, subjects with insulin resistance syndrome have shown high endothelin-1 levels. METHODS Thirty-five subjects were studied: 13 patients with angin pectoris and angiographically normal coronary arteries (CSX group); 9 subjects with insulin resistance syndrome (MSX group) and 13 normal controls. All subjects received an acute intravenous bolus of insulin (0.1 U/kg) combined with euglycemic clamp and forearm indirect calorimetry. Endothelin-1 levels, nitrite/nitrate (NOx) levels, end products of nitric oxide metabolism, glucose infusion rates (index of insulin sensitivity) and their incremental areas (ΔAUCs [are under curves]) were measured during this period. RESULTS Basal endothelin-1 levels were higher in CSX and MSX groups than in normal controls (8.19 ± 0.46 and 6.97 ± 0.88 vs. 3.67 ± 0.99 pg/ml; p < 0.01), while basal NOx levels were significantly higher in MSX group than in CSX and normal controls (36.5 ± 4.0 vs. 24.2 ± 3.3 and 26.8 ± 3.2 mol/liter, p < 0.05). After insulin administration, the ΔAUCs of NOx (p < 0.05) were lower in CSX group than in MSX and normal controls, and the ΔAUCs of endothelin-1 were lower in group CSX than in normal controls. Glucose infusion rate was significantly lower in CSX and MSx groups than in normal controls (p < 0.01), suggesting that in both CSX and MSX groups insulin resistance is present. positive correlation was found between the ΔAUCs of nitric oxide and the AUCs of glucose infusion rate. CONCLUSIONS Blunted nitric oxide and endothelin responsiveness to intravenously infused insulin is typical feature of patients with angin pectoris and angiographically normal coronary arteries and may contribute to the microvascular dysfunction observed in these subjects.