The Glucose-Stimulated insulin Secretion (GSIS) test in vivo is a variant of the glucose tolerance test during which blood is sampled at key time points, in order to measure plasma insulin levels in the basal (fasted) state and after induction of hyperglycemia by a glucose bolus administered either intraperitoneally or orally.
- During an intraperitoneal GSIS, the hyperinsulinemic profile is biphasic, with a first peak at 2 minutes post-injection, a return to basal by 10 minutes post-injection, followed by a second increase in insulinemia 15-30 minutes post-injection.
- During an oral GSIS, a single increase in plasma insulin is observed 15-(30) minutes post-gavage. In response to intestinal glucose absorption, the gut hormones incretins (GLP-1 and GIP) are secreted and potentiate the effect of glucose on insulin secretion. This effect is bypassed by the parenteral administration of glucose during an intraperitoneal GSIS.
An alteration in insulin levels during a GSIS suggests an alteration in insulin secretion which can be further analyzed by the gold standard methods in vivo (the hyperglycemic clamp), and in vitro (insulin secretion in isolated islets).
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Preitner F, Ibberson M, Franklin I, Binnert C, Pende M, Gjinovci A, Hansotia T, Drucker DJ, Wollheim C, Burcelin R, Thorens B. Gluco-incretins control insulin secretion at multiple levels as revealed in mice lacking GLP-1 and GIP receptors. J Clin Invest. 2004 Feb;113(4):635-45.