Korean Diabetes Journal 2000;24(1):1-9.
Published online January 1, 2001.
Mechanism of the lnsulin Secretory Defect by Chronically Elevated Glucose Leveis in Pancreatic lslets: Depletion of lnsulin Content due to Hyperstimulation by Glucose.
Yeon Ah Sung, Young Sun Hong
Department of Internal Medicine, Ewha Womans University College of Medicine, Seoul, Korea.
Abstract
BACKGROUND
Type 2 diabetes is characterized by impaired insulin secretion and decreased insulin sensitivity, although the exact relationship between these two derangements during the development of the disease has not been fully established. Hyperglycemia per se impairs insulin secretion in pancreatic B-cell and the mechanism of impaired insulin by chronic hyperglycemia could be the clue to clarify pathogenesis of type 2 diabetes, and possibly identify the treatments. This study was performed to elucidate the mechanism of impairment of glucose induced insulin secretion by chronic hyperglycemia in pancreatic islets. METHODS: Pancreatic islets were isolated from Sprague-Dawley rats. After incubation of islets in high glucose (20mM) and low glucose (5mM) media for 10 days, glucose (16.7 mM) induced insulin secretion and insulin and DNA content in the islets were measured. Then subcellular distribution of low molecular and heterotrimeric G-proteins were assessed by ADP-ribosylation and radiolabeled GTP binding. RESULTS: 1) Glucose-induced insulin secretion of the islets cultured for 10 days in high glucose media was significantly lower when compared with that in islets cultured in low glucose media (p<0,05) 2) Subcellular distributions of low and heterotrimeric G-protein was not different in the islets cultured in low glucose when compared to those cultured in high glucose. 3) lnsulin content was significantly lower in the islets cultured in high glucose media compared with that in islets cultured in low glucose media (p<0.05) 4) DNA content was not significantly different between the islets cultured in low and high glucose media, and insulin content to DNA ratio was significantly lower in the islets cultured in high glucose media compared with that in islets cultured in low glucose media (p<0.05). CONCLUSION: Impaired insulin secretion to glucose in pancreatic islets exposed to high glucose is caused by depletion of insulin stores affer hyperstimulation.
Key Words: Hyperglycemia, Glucose-induced insulin secretion, Hyperstimulation
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