Hyperinsulinemia, coronary artery disease and syndrome X

Regional Cardiac Unit, Papworth Hospital, Cambridge, England, United Kingdom.

OBJECTIVES. This study was conducted to compare the insulin responses to an oral glucose load in healthy volunteers and patients with syndrome X and patients with coronary artery disease. BACKGROUND. An abnormal coronary flow reserve has been reported in syndrome X by several investigators. However, its cause is not known. Recently, it has been suggested that elevated insulin levels in syndrome X may contribute to microvascular dysfunction. METHODS. Insulin responses to an oral glucose load (75 g) were compared in 17 patients with coronary artery disease, 17 patients with chest pain, positive exercise test findings, normal coronary arteries and impaired coronary flow reserve (syndrome X) and 17 healthy volunteers (control subjects). All were matched for age, gender and body weight. Patients with overt diabetes mellitus or hypertension were excluded. Venous blood samples were taken during fasting and at 30, 60, 90 and 120 min after the glucose load. Samples were analyzed for glucose, immunoreactive insulin and C peptides. RESULTS. There was no significant difference in the glucose levels at all sampling points among the three groups. The C peptide and immunoreactive insulin levels were significantly higher than values in the control group at 60, 90 and 120 min in the groups with syndrome X and coronary artery disease. The peak responses and the areas under the curve were also significantly greater in the latter two groups. There was no significant difference at all sampling points between the group with syndrome X and the group with coronary artery disease. CONCLUSION. Patients with syndrome X have stimulated hyperinsulinemia, which may contribute to the pathophysiology of syndrome X.

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