Glucose Metabolism of Isolated Pancreatic Islets: Difference Between Fetal, Newborn and Adult Rats

1. The concentration of cyclic AMP and the activity of phosphodiesterase were measured in isolated pancreatic islets from fed or 48h-starved mice. 2. Two different phosphodiesterases were detected. Neither the maximum activity nor the Km values of these enzymes were changed by starvation. 3. The concentration of cyclic AMP in non-incubated islets was the same in islets from fed and starved mice. 4. Incubation with 3.3mm-glucose for 5–30min had no effect on the concentration of cyclic AMP, irrespective of the nutritional state of the mice. Incubation with 16.7mm-glucose for 5–30min raised the concentration of cyclic AMP by about 30% in islets from fed mice. This rise was prevented by addition of mannoheptulose (3mg/ml). Incubation with 16.7mm-glucose had no effect on the cyclic AMP content in islets from starved mice. 5. In islets from fed mice 10min incubation with 5mm-caffeine had no effect on the concentration of cyclic AMP in the presence of 3.3 or 16.7mm-glucose, whereas the cyclic AMP content was increased approx. 150% in islets from starved mice. 6. After 10min incubation with 1mm-3-isobutyl-1-methylxanthine in the presence of 3.3 or 16.7mm-glucose the concentration of cyclic AMP was raised by 250% in islets from fed mice and by 400% in islets from starved mice. 7. A threefold function of glucose in the insulin-secretory process is suggested, according to which the decreased islet glucose metabolism is the primary defect in the insulin-secretory mechanism during starvation.

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Melatonin modifies basal and stimulated insulin secretion via NADPH oxidase

Journal of Endocrinology ◽

10.1530/joe-16-0259 ◽

2016 ◽

Vol 231 (3) ◽

pp. 235-244 ◽

Cited By ~ 8

Author(s):

Daniel Simões ◽

Patrícia Riva ◽

Rodrigo Antonio Peliciari-Garcia ◽

Vinicius Fernandes Cruzat ◽

Maria Fernanda Graciano ◽

...

Keyword(s):

Insulin Secretion ◽

Glucose Metabolism ◽

Nadph Oxidase ◽

Pancreatic Islets ◽

Membrane Receptors ◽

Melatonin Treatment ◽

Isolated Pancreatic Islets ◽

Ros Homeostasis ◽

Basal Insulin Secretion ◽

Glucose Stimulated Insulin Secretion

Melatonin is a hormone synthesized in the pineal gland, which modulates several functions within the organism, including the synchronization of glucose metabolism and glucose-stimulated insulin secretion (GSIS). Melatonin can mediate different signaling pathways in pancreatic islets through two membrane receptors and via antioxidant or pro-oxidant enzymes modulation. NADPH oxidase (NOX) is a pro-oxidant enzyme responsible for the production of the reactive oxygen specie (ROS) superoxide, generated from molecular oxygen. In pancreatic islets, NOX-derived ROS can modulate glucose metabolism and regulate insulin secretion. Considering the roles of both melatonin and NOX in islets, the aim of this study was to evaluate the association of NOX and ROS production on glucose metabolism, basal and GSIS in pinealectomized rats (PINX) and in melatonin-treated isolated pancreatic islets. Our results showed that ROS content derived from NOX activity was increased in PINX at baseline (2.8 mM glucose), which was followed by a reduction in glucose metabolism and basal insulin secretion in this group. Under 16.7 mM glucose, an increase in both glucose metabolism and GSIS was observed in PINX islets, without changes in ROS content. In isolated pancreatic islets from control animals incubated with 2.8 mM glucose, melatonin treatment reduced ROS content, whereas in 16.7 mM glucose, melatonin reduced ROS and GSIS. In conclusion, our results demonstrate that both basal and stimulated insulin secretion can be regulated by melatonin through the maintenance of ROS homeostasis in pancreatic islets.

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Ciliary neurotrophic factor promotes survival of neonatal rat islets via the BCL-2 anti-apoptotic pathway

Journal of Endocrinology ◽

10.1677/joe-07-0016 ◽

2007 ◽

Vol 195 (1) ◽

pp. 157-165 ◽

Cited By ~ 22

Author(s):

Luiz F Rezende ◽

Luiz F Stoppiglia ◽

Kleber L A Souza ◽

Alessandro Negro ◽

Francesco Langone ◽

...

Keyword(s):

Insulin Secretion ◽

Glucose Metabolism ◽

Pancreatic Islets ◽

Neurotrophic Factor ◽

Caspase 3 ◽

Ciliary Neurotrophic Factor ◽

Neonatal Rat ◽

Secretory Process ◽

Apoptotic Pathway ◽

Isolated Pancreatic Islets

Ciliary neurotrophic factor (CNTF) belongs to the cytokine family and increases neuron differentiation and/or survival. Pancreatic islets are richly innervated and express receptors for nerve growth factors (NGFs) and may undergo neurotypic responses. CNTF is found in pancreatic islets and exerts paracrine effects in neighboring cells. The aim of this study was to investigate possible effects of CNTF on neonatal rat pancreatic islet differentiation and/or survival. For this purpose, we isolated pancreatic islets from neonatal rats (1–2 days old) by the collagenase method and cultured for 3 days in RPMI medium with (CNTF) or without (CTL) 1 nM CNTF. Thereafter, glucose-stimulated insulin secretion (RIA), general metabolism by (NAD(P)H production; MTS), glucose metabolism (14CO2 production), gene (RT-PCR), protein expression (western blotting), caspase-3 activity (Asp–Glu–Val–Asp (DEVD)), and apoptosis (DNA fragmentation) were analyzed. Our results showed that CNTF-treated islets demonstrated reduced glucose-induced insulin secretion. CNTF treatment did not affect glucose metabolism, as well as the expression of mRNAs and proteins that are crucial for the secretory process. Conversely, CNTF significantly increased mRNA and protein levels related to cell survival, such as Cx36, PAX4, and BCL-2, reduced caspase-3 activity, and islet cells apoptosis, suggesting that CNTF does not affect islet cell differentiation and, instead, acts as a survival factor reducing apoptosis by increasing the expression of the anti-apoptotic BCL-2 protein and decreasing caspase-3 activity.

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