Response to Comment on: Knop et al. (2007) Reduced Incretin Effect in Type 2 Diabetes: Cause or Consequence of the Diabetic State? Diabetes 56:1951–1959

Abstract

We thank Choukem and Gautier (1) for their comment, in which constructive criticism relating to the evaluation of glucagon-like peptide-1 (GLP-1) secretion is raised, concerning our study (2). Secretion of hormones following different stimuli are difficult to estimate from peripheral levels of hormone concentrations. Therefore, hormone responses as measured by concentration changes in the peripheral circulation are often used as indicators of the actual amount of secretion. Choukem and Gautier are right that when the computation of the incremental area under curve (AUC) is based on the difference between the first and the subsequent measures, a possible error of that first measurement will accumulate (3). Therefore, in our studies, we use the average of three baseline values (time points −15, −10, and 0 min) when computing incremental AUCs to minimize the risk of errors at baseline. The incremental AUC values were chosen as a result of the relatively small intact GLP-1 responses observed. We anticipated that less pronounced differences between the responses to the two stimuli (50-g oral glucose tolerance test [OGTT] vs. isoglycemic intravenous glucose infusion) would be easier to detect using the incremental values. In the study in question, we measured both total GLP-1 concentrations (intact and active peptide plus the inactive metabolite) and intact levels (active peptide only) of GLP-1. The intact …