β-Cell function during insulin-modified intravenous glucose tolerance test successfully assessed by the C-peptide minimal model

Using an insulin-modified FSIGT instead of an OGTT limited confounding from gastrointestinal or incretin effects, and together with a minimal-model approach allowed more precise quantification of specific components of glucose metabolism (SI, β-cell function, glucose effectiveness, and hepatic extraction).

“Unlike previous studies that relied on OGTT, we used the insulin-modified FSIGT to limit confounding from gastrointestinal or incretin effects. Together with a minimal-model approach, this allowed more precise quantification of specific components of glucose metabolism, such as SI, β-cell function, glucose effectiveness, and hepatic extraction (15–17).”

Measures of insulin secretion, including β-cell responsivity indices and the minute-by-minute insulin secretory rate, were estimated using FSIGT C-peptide models based on plasma glucose and C-peptide.

“Measures of insulin secretion, including a set of β-cell responsivity indices (Φ) and the minute-by-minute insulin secretory rate (ISR), were estimated using FSIGT C-peptide models (16), based on plasma concentrations of glucose and C-peptide.”

The two prior human in vivo studies did not observe differences in insulin responses, but their measures (acute insulin response to glucose or AUC) relied on circulating insulin concentrations and did not take into account hepatic insulin extraction, whole-body insulin clearance, and prevailing glucose levels, and thus did not independently determine β-cell function.

“Neither of the aforementioned human in vivo studies observed differences in insulin responses (9,10). However, the measures of those two studies (acute insulin response to glucose or AUC) relied on circulating insulin concentrations and did not take into account hepatic insulin extraction, whole-body insulin clearance, and prevailing glucose levels and, thus, did not independently determine β-cell”