Diabetes & Metabolism Journal

Original Articles

The Changes in Insulin Secretion and GTPase Activity after the Exposure to High Glucose in Rat Pancreatic Islets.: Young Sun Hong, Yeon Ah Sung, Nan Ho Kyung; Korean Diabetes J. 2000;24(5):515-523. Published online January 1, 2001

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Abstract: BACKGROUND
Type 2 diabetes mellitus is characterized by defective glucose- induced and glucose-potentiated insulin secretion. Chronic elevation of glucose levels are considered to be a cause of impaired insulin secretion. It has been suggested that such defects in insulin secretion can be related to the alteration in stimulus-secretion coupling. Recent studies have provided evidences for the existence of guanine nucleotide-binding protein (G protein), and the regulatory role of G protein and GTPase activity in stimulus-secretion coupling in pancreatic islets. This study was performed to determine whether the exposure to high glucose concentration alters GTPase activity with decreased insulin secretion in pancreatic islets isolated from normal rats. METHODS: Pancreatic islets isolated from normal Sprague-Dawley rats were incubated in high (20 mM) and low (5 mM) glucose concentration for 48 hours. After incubation, glucose (20 mM) induced insulin secretion was measured. Then subcellular fractions of islets by homogenization and differential centrifugation were obtained and glucose induced inhibition of GTPase activities in each fraction was measured. RESULTS: 1) After 48 hour exposure to 5 mM and 20 mM glucose, insulin secretion in response to 20 mM glucose were 134.4+/-16.8 fmol/10 islets/hr and 90.0+/-10.2 fmol/10 islets/hr, respectively. After the exposure to high glucose, glucose-induced insulin secretion significantly decreased (p<0.05). 2) In each subcellular fraction, there was no significant difference between the islets exposed to 5 mM and 20 mM glucose in the degree of inhibition of GTPase activities by high glucose. CONCLUSION: The exposure to high glucose for 48 hours decreased insulin secretion without any significant differences in the degree of inhibition of GTPase activities. This results suggest that impaired insulin secretion by high glucose is not associated with the change in GTPase activity.

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; Korean Diabetes J. 2000;24(1):1-9. Published online January 1, 2001

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Abstract PDF: 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.

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