The mechanisms by which the enteroinsular axis influences beta-cell function have not been investigated in detail. We performed oral and isoglycemic intravenous (IV) glucose administration in subjects with normal (NGT; n = 11) or impaired glucose tolerance (IGT; n = 10), using C-peptide deconvolution to calculate insulin secretion rates and mathematical modeling to quantitate beta-cell function. The incretin effect was taken to be the ratio of oral to IV responses. In NGT, incretin-mediated insulin release [oral glucose tolerance test (OGTT)/IV ratio = 1.59 +/- 0.18, P = 0.004] amounted to 18 +/- 2 nmol/m(2) (32 +/- 4% of oral response), and its time course matched that of total insulin secretion. The beta-cell glucose sensitivity (OGTT/IV ratio = 1.52 +/- 0.26, P = 0.02), rate sensitivity ( response to glucose rate of change, OGTT/IV ratio = 2.22 +/- 0.37, P = 0.06), and glucose-independent potentiation were markedly higher with oral than IV glucose. In IGT, beta-cell glucose sensitivity (75 +/- 14 vs. 156 +/- 28 pmol center dot min(-1) center dot m(-2) center dot mM(-1) of NGT, P = 0.01) and potentiation were impaired on the OGTT. The incretin effect was not significantly different from NGT in terms of plasma glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide responses, total insulin secretion, and enhancement of beta-cell glucose sensitivity (OGTT/IV ratio = 1.73 +/- 0.24, P = NS vs. NGT). However, the time courses of incretin-mediated insulin secretion and potentiation were altered, with a predominance of glucose-induced vs. incretin-mediated stimulation. We conclude that, under physiological circumstances, incretin-mediated stimulation of insulin secretion results from an enhancement of all dynamic aspects of beta-cell function, particularly beta-cell glucose sensitivity. In IGT, beta-cell function is inherently impaired, whereas the incretin effect is only partially affected.

Impact of incretin hormones on beta-cell function in subjects with normal or impaired glucose tolerance

NATALI, ANDREA;CAMASTRA, STEFANIA;FERRANNINI, ELEUTERIO
2006

Abstract

The mechanisms by which the enteroinsular axis influences beta-cell function have not been investigated in detail. We performed oral and isoglycemic intravenous (IV) glucose administration in subjects with normal (NGT; n = 11) or impaired glucose tolerance (IGT; n = 10), using C-peptide deconvolution to calculate insulin secretion rates and mathematical modeling to quantitate beta-cell function. The incretin effect was taken to be the ratio of oral to IV responses. In NGT, incretin-mediated insulin release [oral glucose tolerance test (OGTT)/IV ratio = 1.59 +/- 0.18, P = 0.004] amounted to 18 +/- 2 nmol/m(2) (32 +/- 4% of oral response), and its time course matched that of total insulin secretion. The beta-cell glucose sensitivity (OGTT/IV ratio = 1.52 +/- 0.26, P = 0.02), rate sensitivity ( response to glucose rate of change, OGTT/IV ratio = 2.22 +/- 0.37, P = 0.06), and glucose-independent potentiation were markedly higher with oral than IV glucose. In IGT, beta-cell glucose sensitivity (75 +/- 14 vs. 156 +/- 28 pmol center dot min(-1) center dot m(-2) center dot mM(-1) of NGT, P = 0.01) and potentiation were impaired on the OGTT. The incretin effect was not significantly different from NGT in terms of plasma glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide responses, total insulin secretion, and enhancement of beta-cell glucose sensitivity (OGTT/IV ratio = 1.73 +/- 0.24, P = NS vs. NGT). However, the time courses of incretin-mediated insulin secretion and potentiation were altered, with a predominance of glucose-induced vs. incretin-mediated stimulation. We conclude that, under physiological circumstances, incretin-mediated stimulation of insulin secretion results from an enhancement of all dynamic aspects of beta-cell function, particularly beta-cell glucose sensitivity. In IGT, beta-cell function is inherently impaired, whereas the incretin effect is only partially affected.
Muscelli, E; Mari, A; Natali, Andrea; Astiarraga, Bd; Camastra, Stefania; Frascerra, S; Holst, Jj; Ferrannini, Eleuterio
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/180327
Citazioni
  • ???jsp.display-item.citation.pmc??? 18
  • Scopus 74
  • ???jsp.display-item.citation.isi??? 65
social impact