Plasma Insulin Response to Glucose as a Coronary Artery Disease Risk Factor in the Normolipidemic Patients with Angiographically Defined Coronary Artery Disease

The possible role of plasma insulin levels as a risk factor in coronary artery disease (CAD) has been studied in 51 normolipidemic (total cholesterol<230mg/dl, triglyceride<150mg/dl) male patients aged 34-80 years. Selective coronary angiography (CAG) was performed in all patients on average within one month of the 75g oral glucose tolerance test (OGTT). CAD was defined as a 75% or greater luminal diameter narrowing of one or more of the major coronary arteries. According to the results of CAG, the patients were divided into two groups: patients with CAD (n=31) and normal coronary arteries (NCA: n=20). The coronary risk factors such as age, blood pressure, smoking, and body mass index were matched for the two groups. Plasma glucose and insulin levels before and 30, 60 and 120 minutes after glucose ingestion were determined in the two groups. Plasma insulin response to glucose ingestion was evaluated by calculating the sum of the insulin levels 0, 30, 60 and 120 minutes after glucose loading. The early insulin response to glucose ingestion (ΔIRI) was calculated as the difference in the values between 0 and 30 minutes. The prevalences of diabetes mellitus (DM) and impaired glucose tolerance (IGT) in the NCA group were 15 and 60%, and those in the CAD group were 10 and 71%, respectively. Thus, the prevalences of abnormal glucose tolerance in the two groups were not significantly different. The values of total cholesterol and triglyceride in the CAD group were similar to those of the NCA group. However, a statistically lower HDL-cholesterol value was observed in the CAD group than in the NCA group. The glucose areas (ΣBG), the insulin areas (ΣIRI), basal insulin levels, and the difference in glucose values between 0 and 30 minutes (ΔBG) were not significantly different. ΔIRI and ΔIRI/ΔBG were significantly higher in the CAD group than in the NCA group. The present data support the hypothesis of the direct atherogenic action of high plasma insulin response during OGTT. In particular, a high early insulin response might be a marker of enhanced liability to the evolution of coronary atherosclerosis.