339-LB: Modulation of Insulin and Glucagon Secretion by Optogenetic Control of Delta-Cell Electrical Activity in Pancreatic Islets

Islet amyloid polypeptide (IAPP, or amylin) is produced in pancreatic β-cells. The intraislet significance of IAPP is still uncertain. In the present study, paracrine effects of endogenous IAPP and somatostatin were investigated in isolated rat pancreatic islets. The intraislet IAPP activity was inhibited with an IAPP antiserum or a specific antagonist [IAPP-(8—37)]. Somatostatin activity was inhibited by immunoneutralization. Basal insulin and glucagon secretion were not affected by the somatostatin and/or IAPP blockade. Arginine-stimulated insulin and glucagon secretion were dose dependently increased by IAPP antiserum, IAPP-(8—37), and somatostatin antiserum, respectively. Arginine-stimulated somatostatin secretion was dose dependently potentiated by IAPP antiserum. Insulin secretion induced by 16.7 mM glucose was enhanced by IAPP antiserum and IAPP-(8—37), respectively. A combination of somatostatin antiserum with IAPP antiserum or IAPP-(8—37) further enhanced the arginine-stimulated insulin and glucagon secretion compared with effects when the blocking reagents were used individually. These results indicate that endogenously produced IAPP tonally inhibits stimulated insulin, glucagon, and somatostatin secretion. Furthermore, the paracrine effects of IAPP and somatostatin are additive.

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Insulin-sparing effects of troglitazone in rat pancreatic islets

Journal of Molecular Endocrinology ◽

10.1677/jme.0.0310061 ◽

2003 ◽

Vol 31 (1) ◽

pp. 61-69 ◽

Cited By ~ 20

Author(s):

LC Bollheimer ◽

S Troll ◽

H Landauer ◽

CE Wrede ◽

J Scholmerich ◽

...

Keyword(s):

Insulin Secretion ◽

Beta Cell ◽

Pancreatic Islets ◽

High Glucose ◽

Cell Function ◽

Glucagon Secretion ◽

Point Of View ◽

Glucose Levels ◽

Rat Pancreatic Islets ◽

Insulin And Glucagon Secretion

Thiazolidinediones (TZDs) have been suggested to act beneficially on pancreatic islet function and on beta-cell viability but data concerning direct effects on isolated islets are controversial. Therefore, we have examined parameters of pancreatic insulin and glucagon secretion and biosynthesis in TZD-exposed rat pancreatic islets under physiological glucose level conditions and under conditions of glucolipotoxicity. Primary rat islets were incubated for 2.5 h with or without troglitazone (10 microM) in 5.6 mM glucose (standard glucose levels) and 16.7 mM glucose (high glucose levels); a subgroup was additionally treated with oleate (200 microM) to simulate acute glucolipotoxicity. Insulin and glucagon secretion, intracellular content and their respective mRNAs were quantified. Newly synthesized insulin was determined by pulse-labeling experiments. Troglitazone reduced insulin secretion at standard and high glucose levels by about one-third (P<or=0.05). Insulin content was decreased at 5.6 mM glucose but increased at 16.7 mM glucose by the presence of troglitazone (P<or=0.05). Newly synthesized insulin mRNA and preproinsulin mRNA decreased by about 20% at standard glucose levels (P<or=0.05). Glucagon secretion was augmented by troglitazone in islets under high glucose conditions by an additional 50% (P<or=0.05). No clear beneficial troglitazone effects were observed under glucolipotoxic conditions. The reduced insulin secretion and biosynthesis at standard glucose levels can be interpreted as an insulin-sparing effect. Troglitazone effects were less pronounced at high glucose alone or in combination with oleate. From a clinical point of view, these results indicate a greater benefit of troglitazone for beta-cell function in hyperinsulinemic, but normoglycemic patients with insulin resistance or early type 2 diabetes without major insulin secretion deficits and/or pronounced hyperglycemia.

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