Hyperinsulinaemia of hypertriglyceridaemia: a reappraisal

The peripheral hyperinsulinaemia of hypertriglyceridaemic subjects has only been defined using insulin immunoassays in which proinsulin and proinsulin fragments cross-react. Relative contributions of pancreatic secretion and hepatic extraction of insulin to this hyperinsulinaemia have not been studied. We, therefore, reassessed the hyperinsulinaemia of hypertriglyceridaemia by measuring fasting plasma concentrations of intact proinsulin, glucose, insulin, and C-peptide in 24 hypertriglyceridaemic subjects with normal glucose tolerance (n = 14) and with impaired glucose intolerance (n = 10) and in normal subjects (n = 14). Hypertriglyceridaemic subjects had higher (p < 0.01) fasting concentrations of insulin and C-peptide and greater (p < 0.01) fasting insulin: C-peptide molar ratios than in control subjects. Fasting intact proinsulin concentrations were similar in hypertriglyceridaemic subjects with normal glucose tolerance and control subjects but these were lower (p < 0.01) than in hypertriglyceridaemic subjects with impaired glucose tolerance. These results suggest that the fasting peripheral hyperinsulinaemia of hypertriglyceridaemic subjects is due to increased pancreatic secretion and reduced hepatic fractional extraction of insulin. The peripheral hyperinsulinaemia of hypertriglyceridaemia appears to reflect peripheral insulin resistance and is not attributable to elevated proinsulin concentrations which are characteristic of impaired glucose tolerance and Type 2 (non-insulin-dependent) diabetes mellitus.