Relationships between insulin secretion, insulin metabolism and insulin resistance in mild glucose intolerance

The aim of this study was to evaluate whether the correlation between insulin resistance and peripheral hyperinsulinaemia existing in mild glucose intolerance corresponds to a relationship between insulin resistance and insulin overproduction by the pancreas. In addition, the possibility that insulin resistance is related to insulin metabolism was examined. Twenty five subjects with fasting normoglycaemia and an abnormal glucose response to the oral glucose tolerance test (OGTT) were studied. Insulin secretion by the pancreas was estimated by means of fasting C-peptide levels in peripheral blood. Insulin resistance was estimated by the rate of glucose disappearance from plasma after i.v. insulin injection. Insulin metabolism was estimated indirectly by the C-peptide: insulin molar ratio. A negative correlation was found between the glucose disappearance rate from plasma after i.v. insulin injection and fasting insulin levels (r = -0.677, p less than 0.001), but not fasting C-peptide concentrations (r = -0.164, p = NS). Glucose disappearance rate from plasma correlated positively with the C-peptide: insulin molar ratio (r = 0.626, p less than 0.001). These results suggest that in mild glucose intolerance insulin resistance and insulin secretion by the pancreas are not related phenomena, and that the defect responsible for insulin resistance might also be implicated in the impaired insulin metabolism.