Browsing by Author "Tong, Jenny"
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Item Open Access Acute administration of unacylated ghrelin has no effect on Basal or stimulated insulin secretion in healthy humans.(Diabetes, 2014-07) Tong, Jenny; Davis, Harold W; Summer, Suzanne; Benoit, Stephen C; Haque, Ahrar; Bidlingmaier, Martin; Tschöp, Matthias H; D'Alessio, DavidUnacylated ghrelin (UAG) is the predominant ghrelin isoform in the circulation. Despite its inability to activate the classical ghrelin receptor, preclinical studies suggest that UAG may promote β-cell function. We hypothesized that UAG would oppose the effects of acylated ghrelin (AG) on insulin secretion and glucose tolerance. AG (1 µg/kg/h), UAG (4 µg/kg/h), combined AG+UAG, or saline were infused to 17 healthy subjects (9 men and 8 women) on four occasions in randomized order. Ghrelin was infused for 30 min to achieve steady-state levels and continued through a 3-h intravenous glucose tolerance test. The acute insulin response to glucose (AIRg), insulin sensitivity index (SI), disposition index (DI), and intravenous glucose tolerance (kg) were compared for each subject during the four infusions. AG infusion raised fasting glucose levels but had no effect on fasting plasma insulin. Compared with the saline control, AG and AG+UAG both decreased AIRg, but UAG alone had no effect. SI did not differ among the treatments. AG, but not UAG, reduced DI and kg and increased plasma growth hormone. UAG did not alter growth hormone, cortisol, glucagon, or free fatty acid levels. UAG selectively decreased glucose and fructose consumption compared with the other treatments. In contrast to previous reports, acute administration of UAG does not have independent effects on glucose tolerance or β-cell function and neither augments nor antagonizes the effects of AG.Item Open Access Ghrelin Regulation of Glucose Metabolism.(Journal of neuroendocrinology, 2019-03-08) Gray, Sarah M; Page, Laura C; Tong, JennyGhrelin and its receptor, the growth hormone secretagogue receptor 1a (GHSR1a), are implicated in the regulation of glucose metabolism through direct actions in the pancreatic islet as well as peripheral insulin-sensitive tissues and brain. While many studies have explored the role of ghrelin in glucose tolerance and insulin secretion, a complete mechanistic understanding has yet to be elucidated. This review highlights the local expression and function of ghrelin and GHSR1a in pancreatic islets and how this axis may modulate insulin secretion from pancreatic β-cells. Additionally, we discuss the effect of ghrelin on in vivo glucose metabolism in rodents and humans and the metabolic circumstances under which ghrelin action may predominate. This article is protected by copyright. All rights reserved.Item Open Access Ghrelin suppresses glucose-stimulated insulin secretion and deteriorates glucose tolerance in healthy humans.(Diabetes, 2010-09) Tong, Jenny; Prigeon, Ronald L; Davis, Harold W; Bidlingmaier, Martin; Kahn, Steven E; Cummings, David E; Tschöp, Matthias H; D'Alessio, DavidOBJECTIVE: The orexigenic gut hormone ghrelin and its receptor are present in pancreatic islets. Although ghrelin reduces insulin secretion in rodents, its effect on insulin secretion in humans has not been established. The goal of this study was to test the hypothesis that circulating ghrelin suppresses glucose-stimulated insulin secretion in healthy subjects. RESEARCH DESIGN AND METHODS: Ghrelin (0.3, 0.9 and 1.5 nmol/kg/h) or saline was infused for more than 65 min in 12 healthy patients (8 male/4 female) on 4 separate occasions in a counterbalanced fashion. An intravenous glucose tolerance test was performed during steady state plasma ghrelin levels. The acute insulin response to intravenous glucose (AIRg) was calculated from plasma insulin concentrations between 2 and 10 min after the glucose bolus. Intravenous glucose tolerance was measured as the glucose disappearance constant (Kg) from 10 to 30 min. RESULTS: The three ghrelin infusions raised plasma total ghrelin concentrations to 4-, 15-, and 23-fold above the fasting level, respectively. Ghrelin infusion did not alter fasting plasma insulin or glucose, but compared with saline, the 0.3, 0.9, and 1.5 nmol/kg/h doses decreased AIRg (2,152 +/- 448 vs. 1,478 +/- 2,889, 1,419 +/- 275, and 1,120 +/- 174 pmol/l) and Kg (0.3 and 1.5 nmol/kg/h doses only) significantly (P < 0.05 for all). Ghrelin infusion raised plasma growth hormone and serum cortisol concentrations significantly (P < 0.001 for both), but had no effect on glucagon, epinephrine, or norepinephrine levels (P = 0.44, 0.74, and 0.48, respectively). CONCLUSIONS: This is a robust proof-of-concept study showing that exogenous ghrelin reduces glucose-stimulated insulin secretion and glucose disappearance in healthy humans. Our findings raise the possibility that endogenous ghrelin has a role in physiologic insulin secretion, and that ghrelin antagonists could improve beta-cell function.Item Open Access The D-Day of ghrelin.(Mol Metab, 2016-07) Tong, Jenny; Mauvais-Jarvis, Franck