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-cell insulin secretion in 24-h multiple-meal test1Department of Systems Analysis and Informatics, University of Rome "La Sapienza"; 2Institute of Systems Analysis and Computer Science-Italian National Research Council; 3Liver Unit, Bambino Gesù Hospital and Research Institute; and 4Institute of Internal Medicine, Catholic University, School of Medicine, Rome, Italy
Submitted 17 October 2006 ; accepted in final form 26 February 2007
There is experimental evidence that a source of fatty acids (FAs) that is either exogenous or endogenous is necessary to support normal insulin secretion. Therefore, FAs comodulate the glucose-induced pancreatic insulin secretion. To assess the role of FAs, 16 morbidly obese nondiabetic patients and 6 healthy volunteers were studied. The controls and the obese subjects, before and after diet-induced weight loss, spent 24 h in a calorimetric chamber, where they consumed standardized meals. Hourly blood samples were drawn from a central venous catheter for the measurement of glucose, C-peptide, and nonesterified fatty acid (NEFA) concentrations. Insulin sensitivity was measured (as the M value) by euglycemic hyperinsulinemic clamp. In the present study, we propose a mathematical model in which insulin secretion rate (ISR) is expressed as a function of both plasma glucose and NEFA concentrations. Model parameters, obtained by fitting the individual experimental data of plasma C-peptide concentration, gave an estimated ISR comparable with that obtained by the deconvolution method. To evaluate the performance of the model in an experimental condition in which incretin effect was minimized, previous data on insulin secretion following a butter load and subsequent hyperglycemic clamp were reanalyzed. This model of nutrient-stimulated insulin secretion is the first attempt to represent in a simple way the interaction between glucose and NEFA in the regulation of insulin secretion in the
-cell and explains, at least in part, the "potentiation factor" used in previous models to account for other control factors different from glucose after either an intravenous infusion of glucose or a mixed meal.
nonesterified fatty acid; mathematical model
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