[Analysis of islet B cell reserve in patients with NIDDM]

The plasma glucose and insulin response to oral glucose or carbohydrate meal tolerance tests were determined in 78 normal controls, 71 persons with IGT and 110 patients with NIDDM. The results showed that: (1) The fasting serum insulin levels and insulin/glucose ratio were all higher in persons with IGT than those in the normal controls, and they were normal in diabetics with fasting plasma glucose less than 7.8 mmol/L. In diabetics with fasting plasma glucose at 7.8-20.3 mmol/L, fasting insulin levels were within normal limit, but the values of insulin/glucose ratio were significantly decreased. (2) After glucose challenge, the values of serum insulin/glucose ratio were all increased in IGT, but were progressively decreased in diabetics as fasting plasma glucose gradually became higher. (3) Fasting serum insulin levels were increased in normal weight and over-weight individuals with IGT. But in those with diabetes, fasting insulin was increased in comparison with normal controls. When fasting plasma glucose was greater than 11.1 mmol/L, insulin/glucose ratio was decreased significantly. Our data suggests that the increased insulin secretion in persons with IGT was due to peripheral resistance and relative insulin insufficiency, and that hyperglycemia could compensate for B cell impairment.