Diurnal rhythm of insulin sensitivity in subjects with normal and impaired glucose tolerance

We studied the insulin sensitivity in 5 normal subjects and 5 subjects with impaired carbohydrate tolerance using the glucose controlled insulin infusion system (BIOSTATOR). During a fixed glucose infusion rate of 2 mg/kg b.w./min, the computer program was set to maintain the plasma glucose concentration at 4.44 mmol/l. The ratio of infused exogenous insulin to infused glucose served as a measure of insulin sensitivity. Calculating the average insulin glucose ratio for 24 hours, the mean values amounted to 3531 and 9319 ng/gm (p less than 0.01) in subjects with normal and impaired carbohydrate tolerance, respectively, indicating that insulin resistance is the main cause of decreased glucose utilization in the latter group. Circadian rhythms of insulin sensitivity occur in both groups in a similar fashion. The insulin sensitivity was higher in the afternoon (1200-1800) as compared to the night. Thus, diurnal variations in insulin sensitivity are independent of disturbances of glucose metabolism.