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1.
Diabetologia ; 54(6): 1379-87, 2011 Jun.
Article in English | MEDLINE | ID: mdl-21347622

ABSTRACT

AIMS/HYPOTHESIS: The hormone glucagon-like peptide 1 (GLP-1) is released in response to a meal from the intestinal L-cells, where it is processed from proglucagon by the proconvertase (PC)1/3. In contrast, in the adult islets proglucagon is processed to glucagon by the PC2 enzyme. The aim of the study was to evaluate if, during the development of diabetes, alpha cells produce GLP-1 that, in turn, might trigger beta cell growth. METHODS: Beta cell mass, GLP-1 and insulin levels were measured in the gerbil Psammomys obesus (P. obesus), a rodent model of nutritionally induced diabetes. Furthermore, the presence of biologically active forms of GLP-1 and PC1/3 in alpha cells was demonstrated by immunofluorescence, and the release of GLP-1 from isolated P. obesus, mouse and human islets was investigated. RESULTS: During the development of diabetes in P. obesus, a significant increase in GLP-1 was detected in the portal vein (9.8 ± 1.5 vs 4.3 ± 0.7 pmol/l, p < 0.05), and in pancreas extracts (11.4 ± 2.2 vs 5.1 ± 1.3 pmol/g tissue, p < 0.05). Freshly isolated islets from hyperglycaemic animals released more GLP-1 following 24 h culture than islets from control animals (28.2 ± 4.4 pmol/l vs 5.8 ± 2.4, p < 0.01). GLP-1 release was increased from healthy P. obesus islets following culture in high glucose for 6 days (91 ± 9.1 pmol/l vs 28.8 ± 6.6, p < 0.01). High levels of GLP-1 were also found to be released from human islets. PC1/3 colocalised weakly with alpha cells. CONCLUSIONS/INTERPRETATION: GLP-1 release from alpha cells is upregulated in P. obesus during the development of diabetes. A similar response is seen in islets exposed to high glucose, which supports the hypothesis that GLP-1 released from alpha cells promotes an increase in beta cell mass and function during metabolic challenge such as diabetes.


Subject(s)
Diabetes Mellitus/metabolism , Gerbillinae/metabolism , Glucagon-Like Peptide 1/metabolism , Glucagon-Secreting Cells/metabolism , Hyperglycemia/metabolism , Obesity/metabolism , Up-Regulation/physiology , Adaptation, Physiological/physiology , Adult , Animals , Cell Proliferation/drug effects , Cells, Cultured , Diabetes Mellitus/etiology , Diabetes Mellitus/pathology , Diet/adverse effects , Disease Models, Animal , Dose-Response Relationship, Drug , Female , Glucagon-Secreting Cells/drug effects , Glucagon-Secreting Cells/pathology , Glucose/pharmacology , Humans , Hyperglycemia/pathology , Insulin/metabolism , Insulin-Secreting Cells/drug effects , Insulin-Secreting Cells/metabolism , Insulin-Secreting Cells/pathology , Islets of Langerhans/drug effects , Islets of Langerhans/metabolism , Islets of Langerhans/pathology , Male , Mice , Middle Aged , Obesity/genetics , Obesity/pathology
2.
Diabetologia ; 53(10): 2220-3, 2010 Oct.
Article in English | MEDLINE | ID: mdl-20585936

ABSTRACT

AIMS/HYPOTHESIS: Gastrin has been implicated in islet growth/neogenesis, and proton pump inhibitors (PPIs) have been shown to increase endogenous gastrin levels in animals and humans. Therefore, we investigated the effect of PPIs in a model of type 2 diabetes, Psammomys obesus. METHODS: P. obesus (morning blood glucose [mBG] 16.9 +/- 0.6 mmol/l) were treated with vehicle or different doses (1-15 mg/kg) of lansoprazole for 17 days. RESULTS: Treatment with lansoprazole resulted in up to ninefold dose-dependent increases in endogenous gastrin levels (p < 0.05 for 10 mg/kg lansoprazole vs vehicle). There was a significant reduction in mBG levels in all animals in the high-dose lansoprazole groups during the 17 day treatment period, whereas there was no significant improvement in mBG in animals in the vehicle groups. The mBG at end of study was 18.2 +/- 2.1, 8.7 +/- 2.2 (p < 0.01), and 6.1 +/- 2.3 (p < 0.001) mmol/l for vehicle and lansoprazole 10 and 15 mg/kg, respectively. The animals treated with 15 mg/kg lansoprazole, compared with vehicle, had a 2.3-fold increase in the intensity of insulin staining in beta cells (p=0.0002) and 50% higher beta cell mass (p=0.04). CONCLUSIONS/INTERPRETATIONS: The PPI lansoprazole had significant glucose-lowering effects in an animal model of type 2 diabetes, an effect that is most likely mediated through an increase in endogenous gastrin levels.


Subject(s)
2-Pyridinylmethylsulfinylbenzimidazoles/therapeutic use , Blood Glucose/drug effects , Diabetes Mellitus, Type 2/drug therapy , Hyperglycemia/drug therapy , Proton Pump Inhibitors , 2-Pyridinylmethylsulfinylbenzimidazoles/administration & dosage , Analysis of Variance , Animals , Blood Glucose/metabolism , Diabetes Mellitus, Type 2/metabolism , Disease Models, Animal , Dose-Response Relationship, Drug , Enzyme Inhibitors/therapeutic use , Female , Gastrins/blood , Gerbillinae , Immunohistochemistry , Insulin/metabolism , Insulin-Secreting Cells/drug effects , Insulin-Secreting Cells/metabolism , Lansoprazole , Male
3.
Diabetes Obes Metab ; 11(8): 795-803, 2009 Aug.
Article in English | MEDLINE | ID: mdl-19519868

ABSTRACT

AIM/HYPOTHESIS: Combination therapies are increasingly common in the clinical management of type 2 diabetes. We investigated to what extent combined treatment with the human glucagon-like peptide-1 (GLP-1) analogue liraglutide and the dual PPARalpha/gamma agonist ragaglitazar would improve glycaemic control in overtly diabetic Zucker diabetic fatty (ZDF) rats. METHODS: Ninety overtly diabetic male ZDF rats were stratified into groups with matched haemoglobin A1c (HbA1c) (9.0+/-0.1%). Liraglutide (15 and 50 microg/kg subcutaneously twice daily), ragaglitazar (1 and 3 mg/kg perorally once daily) and their vehicles were studied as monotherapy and in combination in a 3x3 factorial design. RESULTS: After 4-week treatment, synergistic effects on HbA1c, non-fasting morning blood glucose (BG) and/or 24-h BG profiles were observed with three of the four combinations. The relationship between plasma insulin and BG in combination-treated animals approached that of historical lean ZDF rats representing normal glucose homeostasis, suggesting that insulin secretion and insulin sensitivity were markedly improved. Increased insulin immunostaining in islets further supports the improved beta-cell function and/or insulin sensitivity in combination-treated animals. The synergistic effect on glycaemic control was found without a similar synergistic increase in beta-cell mass in the combination groups. CONCLUSIONS/INTERPRETATION: Our data demonstrate that combination treatment with a human GLP-1 analogue and a dual PPARalpha/gamma agonist through distinct mechanism of actions synergistically improves glycaemic control in the ZDF rat.


Subject(s)
Blood Glucose/drug effects , Diabetes Mellitus/drug therapy , Glucagon-Like Peptide 1/analogs & derivatives , Hypoglycemic Agents/pharmacology , Oxazines/therapeutic use , Phenylpropionates/therapeutic use , Animals , Cell Proliferation/drug effects , Disease Models, Animal , Drug Synergism , Glucagon-Like Peptide 1/therapeutic use , Glycated Hemoglobin/analysis , Homeodomain Proteins/analysis , Homeostasis/drug effects , Immunohistochemistry , Insulin/blood , Insulin-Secreting Cells/drug effects , Insulin-Secreting Cells/immunology , Liraglutide , Rats , Rats, Zucker , Trans-Activators/analysis
4.
Diabetes Obes Metab ; 10(4): 301-11, 2008 Apr.
Article in English | MEDLINE | ID: mdl-18333889

ABSTRACT

OBJECTIVE: Severe insulin resistance and impaired pancreatic beta-cell function are pathophysiological contributors to type 2 diabetes, and ideally, antihyperglycaemic strategies should address both. RESEARCH DESIGN AND METHODS: Therapeutic benefits of combining the long-acting human glucagon-like peptide-1 (GLP-1) analog, liraglutide (0.4 mg/kg/day), with insulin sensitizer, pioglitazone (10 mg/kg/day), were assessed in severely diabetic Zucker diabetic fatty rats for 42 days. Impact on glycaemic control was assessed by glycated haemoglobin (HbA(1C)) at day 28 and by oral glucose tolerance test at day 42. RESULTS: Liraglutide and pioglitazone synergistically improved glycaemic control as reflected by a marked decrease in HbA(1C) (liraglutide + pioglitazone: 4.8 +/- 0.3%; liraglutide: 8.8 +/- 0.6%; pioglitazone: 7.9 +/- 0.4%; vehicle: 9.7 +/- 0.3%) and improved oral glucose tolerance at day 42 (area under the curve; liraglutide + pioglitazone: 4244 +/- 445 mmol/l x min; liraglutide: 7164 +/- 187 mmol/l x min; pioglitazone: 7430 +/- 446 mmol/l x min; vehicle: 8093 +/- 139 mmol/l x min). A 24-h plasma glucose profile at day 38 was significantly decreased only in the liraglutide + pioglitazone group. In addition, 24-h insulin profile was significantly elevated only in the liraglutide + pioglitazone group. Liraglutide significantly decreased food intake alone and in combination with pioglitazone, while pioglitazone alone increased cumulated food intake. As a result, rats on liraglutide alone gained significantly less weight than vehicle-treated rats, whereas rats on pioglitazone alone gained significantly more body weight than vehicle-treated rats. However, combination therapy with liraglutide and pioglitazone caused the largest weight gain, probably reflecting marked improvement of energy balance because of reduction of glucosuria. CONCLUSIONS: Combination therapy with insulinotropic GLP-1 agonist liraglutide and insulin sensitizer, pioglitazone, improves glycaemic control above and beyond what would be expected from additive effects of the two antidiabetic agents.


Subject(s)
Diabetes Mellitus, Type 2/drug therapy , Glucagon-Like Peptide 1/analogs & derivatives , Hypoglycemic Agents/therapeutic use , Thiazolidinediones/therapeutic use , Animals , Biomarkers/blood , Blood Glucose/analysis , Diabetes Mellitus, Type 2/blood , Diabetes Mellitus, Type 2/pathology , Drug Synergism , Drug Therapy, Combination , Energy Metabolism/drug effects , Glucagon-Like Peptide 1/therapeutic use , Glucose Tolerance Test , Glycated Hemoglobin/analysis , Humans , Islets of Langerhans/drug effects , Islets of Langerhans/pathology , Liraglutide , Male , Models, Animal , Pioglitazone , Rats , Rats, Zucker , Weight Gain/drug effects
5.
Diabetes Obes Metab ; 9 Suppl 2: 170-9, 2007 Nov.
Article in English | MEDLINE | ID: mdl-17919191

ABSTRACT

Increased knowledge about beta-cell mass and function is important for our understanding of the pathophysiology of type 2 diabetes (T2DM). The relationship between the two is difficult to study in humans, whereas animal models allow studies of consequences of, for example, reduction of beta-cell mass and induction of obesity and procurement of the pancreas for histological examination. An overview of results obtained in the Göttingen minipig in relation to beta-cell function, and mass is provided here. Effects of a primary reduction of beta-cell mass have indicated that not all of the defects of pulsatile insulin secretion in human T2DM can be explained by reduced beta-cell mass. Furthermore, induction of obesity has shown deterioration of beta-cell function and morphological changes in the pancreas. As in humans, obesity leads to an increased beta-cell volume in the minipig, and based on the increased number of islets, neogenesis of islets is an important factor in expansion of beta-cell mass in this species. Measurement of beta-cell function as an estimate of beta-cell mass is, at present, the only method possible in humans, and this approach has been validated using lean and obese minipigs with a range of beta-cell mass. The effects on beta-cell function and mass of obesity of longer duration and/or more pronounced hyperglycaemia remains to be determined, but the models developed so far represent a valuable tool for such investigations.


Subject(s)
Diabetes Mellitus, Experimental/pathology , Insulin-Secreting Cells/pathology , Insulin/metabolism , Obesity/pathology , Animals , Disease Models, Animal , Humans , Insulin Secretion , Insulin-Secreting Cells/metabolism , Pancreas/pathology , Swine , Swine, Miniature
6.
Am J Physiol Endocrinol Metab ; 288(2): E412-21, 2005 Feb.
Article in English | MEDLINE | ID: mdl-15479954

ABSTRACT

Herein, we bridge beta-cell function and morphology in minipigs. We hypothesized that different aspects of beta-cell dysfunction are present in obesity and obesity with reduced beta-cell mass by using pulsatile insulin secretion as an early marker. Measures for beta-cell function (glucose and arginine stimulation plus baseline and glucose-entrained pulsatile insulin secretion) and islet morphology were studied in long-term (19-20 mo) obese (n = 5) and obese beta-cell-reduced [nicotinamide + streptozotocin (STZ), n = 5] minipigs and normal controls, representing different stages in the development toward type 2 diabetes. Acute insulin response (AIR) to glucose and arginine were, surprisingly, normal in obese (0.3 g/kg glucose: AIR = 246 +/- 119 vs. 255 +/- 61 pM in control; 67 mg/kg arginine: AIR = 230 +/- 124 vs. 214 +/- 85 pM in control) but reduced in obese-STZ animals (0.3 g/kg glucose: AIR = 22 +/- 36, P < 0.01; arginine: AIR = 87 +/- 92 pM, P < 0.05 vs. control). Baseline pulsatile insulin secretion was reduced in obese (59 +/- 16 vs. 76 +/- 16% in control, P < 0.05) and more so in obese-STZ animals (43 +/- 13%, P < 0.01), whereas regularity during entrainment was increased in obese animals (approximate entropy: 0.85 +/- 0.14 vs. 1.13 +/- 0.13 in control, P < 0.01). Beta-cell mass (mg/kg body wt) was normal in obese and reduced in obese-STZ animals, with pancreatic fat infiltration in both groups. In conclusion, obesity and insulin resistance are not linked with a general reduction of beta-cell function, but dynamics of insulin secretion are perturbed. The data suggest a sequence in the development of beta-cell dysfunction, with the three groups representing stages in the progression from normal physiology to diabetes, and assessment of pulsatility as the single most sensitive marker of beta-cell dysfunction.


Subject(s)
Diabetes Mellitus, Experimental/metabolism , Diabetes Mellitus, Experimental/pathology , Insulin/metabolism , Islets of Langerhans/metabolism , Islets of Langerhans/pathology , Obesity/metabolism , Obesity/pathology , Animals , Blood Glucose/analysis , Cells, Cultured , Diabetes Mellitus, Experimental/chemically induced , Diabetes Mellitus, Experimental/complications , Dietary Fats/metabolism , Insulin Secretion , Islets of Langerhans/drug effects , Male , Niacinamide , Obesity/chemically induced , Obesity/complications , Reference Values , Streptozocin , Swine , Swine, Miniature
7.
Diabetologia ; 47(11): 1873-8, 2004 Nov.
Article in English | MEDLINE | ID: mdl-15565374

ABSTRACT

AIMS/HYPOTHESIS: A progressive loss of beta cell function and mass are important contributory factors in the development and progression of type 2 diabetes. The aim of this study was to evaluate the effects of a primary reduction in beta cell mass on beta cell function in vivo and in the perfused pancreas and to relate these characteristics to beta cell mass. METHODS: The beta cell mass of six Göttingen minipigs was reduced chemically (using 67 mg/kg nicotinamide and 125 mg/kg streptozotocin). Six untreated minipigs were kept as control animals. Insulin responses were evaluated in vivo using the mixed meal tolerance test (2 g/kg oral glucose) and in the isolated perfused pancreata from the same animals by stimulation with glucose, glucagon-like peptide-1 or arginine. RESULTS: Beta cell mass was reduced in the beta-cell-reduced animals compared with the control minipigs (182+/-76 vs 464+/-156 mg, p<0.01). AUC(glucose) was increased in the beta-cell-reduced animals (1383+/-385 vs 853+/-113 mmol.l(-1).min in control minipigs, p<0.01), as was the insulin response to oral glucose per unit of beta cell mass (123+/-84 vs 56+/-24 pmol.l(-1).min.mg(-1), p<0.05). Total in vitro insulin secretion was increased per unit of beta cell mass in nicotinamide + streptozotocin pancreata compared to controls (83.7+/-45.9 vs 34.6+/-14.4 nmol/mg beta cells, p<0.05) with responses to glucose and glucagon-like peptide-1 showing a partial compensation for reduced beta cell mass, whereas no compensation was seen in response to arginine. CONCLUSIONS/INTERPRETATION: A primary reduction in beta cell mass impairs glucose tolerance and leads to a compensatory increase in insulin secretion from the remaining beta cells after oral glucose in vivo, which is even more apparent in the perfused pancreas. It remains to be determined whether this compensation can be maintained in the long term.


Subject(s)
Diabetes Mellitus, Experimental/pathology , Insulin/metabolism , Islets of Langerhans/anatomy & histology , Pancreas/pathology , Animals , Area Under Curve , Blood Glucose/metabolism , Disease Models, Animal , Dose-Response Relationship, Drug , Fasting , Glucagon/pharmacology , Glucagon-Like Peptide 1 , Glucose/pharmacology , Insulin Secretion , Islets of Langerhans/drug effects , Islets of Langerhans/metabolism , Kinetics , Male , Niacinamide , Peptide Fragments/pharmacology , Perfusion , Protein Precursors/pharmacology , Reference Values , Swine , Swine, Miniature
8.
Diabetologia ; 47(5): 892-908, 2004 May.
Article in English | MEDLINE | ID: mdl-15105991

ABSTRACT

AIMS/HYPOTHESIS: Type 1 diabetes mellitus is a multifactorial autoimmune disease characterised by selective destruction of beta cells in the islets of Langerhans. We have previously shown that IL-1 beta modulates beta cell function, causes beta cell death and induces expression changes in 82 out of 1815 protein spots detected by two-dimensional gel electrophoresis (2-DGE) in diabetes-prone bio-breeding (BB-DP) rat islets in vitro. The aim of this study was to describe the relevance of these proteins in the development of diabetes in vivo. METHODS: Syngeneic neonatal islets ( n=200) were transplanted under the kidney capsule of 30-day-old BB-DP and control rats, removed to different time points after transplantation or at the onset of diabetes, and metabolically labelled with S(35)-methionine for 2-DGE. The 82 proteins were re-localised and followed. In addition, transplants were examined for expression of IL-1 beta mRNA by in situ hybridisation. RESULTS: All 82 proteins could be re-localised in all syngeneic transplants from BB-DP and control rats. A total of 60 of the 82 proteins were changed during development of diabetes. Of the 82 proteins, 32 were changed in expression at the onset of diabetes compared to non-diabetic BB-DP rats, and 25 of these were changed as by IL-1 beta in vitro. Highest expression of IL-1 beta mRNA was found at the onset of diabetes. CONCLUSIONS/INTERPRETATION: IL-1 beta-induced protein expression changes in islets in vitro also occur in vivo and change in a complex pattern during the development of diabetes in the BB-DP rat. No single protein seems to be responsible for the development of diabetes, but rather the cumulative numbers of changes seem to interfere with the intracellular stability of the beta cell.


Subject(s)
Diabetes Mellitus, Type 1/genetics , Gene Expression Regulation/immunology , Interleukin-1/genetics , Animals , Cell Separation/methods , In Situ Hybridization , Islets of Langerhans/cytology , Islets of Langerhans/drug effects , Islets of Langerhans/immunology , RNA, Messenger/genetics , Rats , Rats, Inbred BB
9.
Diabetologia ; 46(2): 195-202, 2003 Feb.
Article in English | MEDLINE | ID: mdl-12627318

ABSTRACT

AIMS/HYPOTHESIS: Type 2 diabetes is associated with impaired insulin action and secretion, including disturbed pulsatile release. Impaired pulsatility has been related to impaired insulin action, thus providing a possible link between release and action of insulin. Furthermore, progressive loss of beta-cell mass has been implicated in the pathogenesis of Type 2 diabetes. The aim of this study was to evaluate a possible link between loss of beta-cell mass and impaired pulsatile insulin secretion with special focus on glucose responsiveness of insulin secretion. METHODS: The kinetic and dynamic profiles of insulin in Göttingen minipigs are favourable for studies on pulsatility and a model of diabetes with reduced beta-cell mass has recently been established. Pigs were studied before (n=14) and after (n=10) reduction of beta-cell mass by nicotinamide (67 mg/kg) and streptozotocin (125 mg/kg) from 17.7+/-4.7 (normal animals, n=5) to 6.1+/-2.0 mg/kg. Pulsatile insulin secretion was examined during basal (n=8 normal, n=6 beta-cell reduced) and glucose entrained (n=6 normal, n=4 beta-cell reduced) conditions. Insulin concentration time series were analysed by autocorrelation and spectral analyses for periodicities and regularity, and by deconvolution for pulse frequency, mass and amplitude. RESULTS: Reduction of beta-cell mass and secondary hyperglycaemia resulted in correspondingly (r=0.7421, p=0.0275) reduced pulse mass (42% of normal during basal and 31% during entrained conditions) with normal periodicity (6.6+/-2.2 vs 5.8+/-2.4 min, p=0.50), regularity and entrainability of insulin secretion. CONCLUSION/INTERPRETATION: Neither beta-cell loss, nor 2 weeks of slight hyperglycaemia, as seen in the beta-cell-reduced minipig, probably accounts for the disturbed insulin pulsatility observed in human Type 2 diabetes.


Subject(s)
Insulin/metabolism , Islets of Langerhans/physiopathology , Animals , Cell Death , Drug Combinations , Hyperglycemia/metabolism , Insulin Secretion , Islets of Langerhans/drug effects , Islets of Langerhans/pathology , Male , Niacinamide/pharmacology , Periodicity , Pulsatile Flow , Streptozocin/pharmacology , Swine , Swine, Miniature
10.
Pflugers Arch ; 442(1): 19-26, 2001 Apr.
Article in English | MEDLINE | ID: mdl-11374064

ABSTRACT

Somatostatin hyperpolarized rat pancreatic alpha-cells and inhibited spontaneous electrical activity by activating a low-conductance K+ channel (0.9 pS with physiological ionic gradients). This channel was insensitive to tolbutamide (a blocker of ATP-sensitive K+ channels) and apamin (an inhibitor of small-conductance Ca(2+)-activated K+ channels). Channel activation was prevented by pre-treating the cells with pertussis toxin, indicating the involvement of G-proteins. A direct interaction between an inhibitory G-protein and the somatostatin-activated K+ channel is suggested by the finding that intracellular application of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma-S) and the G beta gamma subunit of G-proteins resulted in a transient stimulation of the current. Activation of the K+ current by somatostatin was inhibited by intracellular dialysis with specific antibodies to Gi1/2 and was not seen in cells treated with antisense oligonucleotides against G-proteins of the subtype Gi2. We conclude that somatostatin suppresses alpha-cell electrical activity by a Gi2-protein-dependent mechanism, which culminates in the activation of a sulphonylurea- and apamin-insensitive low-conductance K+ channel.


Subject(s)
GTP-Binding Protein alpha Subunits, Gi-Go/physiology , Islets of Langerhans/physiology , Potassium Channels/physiology , Receptors, Somatostatin/physiology , Animals , Antibodies/pharmacology , Apamin/pharmacology , Calcium/pharmacology , Dialysis , Electric Conductivity , GTP-Binding Protein alpha Subunits, Gi-Go/immunology , Guanosine 5'-O-(3-Thiotriphosphate)/pharmacology , Male , Pertussis Toxin , Potassium Channel Blockers , Potassium Channels/drug effects , Rats , Rats, Inbred Lew , Somatostatin/pharmacology , Tolbutamide/pharmacology , Virulence Factors, Bordetella/pharmacology
11.
Pflugers Arch ; 438(4): 428-36, 1999 Sep.
Article in English | MEDLINE | ID: mdl-10519134

ABSTRACT

We have monitored whole-cell and single channel ATP-sensitive K+ (KATP) currents in isolated rat glucagon-secreting pancreatic A-cells. Tolbutamide produced a concentration-dependent decrease in the whole-cell KATP conductance (Ki = 6 microM) and initiated action potential firing. The K+ channel opener diazoxide, but not cromakalim or pinacidil, inhibited electrical activity and increased the whole-cell K+ conductance fourfold. ATP applied to the intracellular face of the membrane inhibited KATP channel activity with a Ki of 17 microM, an effect that could be counteracted by Mg-ADP and Mg-GDP. GTP and UTP did not affect KATP channel activity. Phosphatidylinositol 4,5-bisphosphate activated KATP channels inhibited by ATP after a delay of 90 s. In situ hybridisation demonstrated the expression of the mRNA encoding KATP channel subunits Kir6.2 and SUR1 but not Kir6.1 and SUR2. We conclude that rat pancreatic A-cells express KATP channels with the nucleotide-, sulphonylurea- and K+ channel-opener sensitivities expected for a channel formed by Kir6.2 and SUR1 subunits.


Subject(s)
ATP-Binding Cassette Transporters , Adenosine Triphosphate/physiology , Islets of Langerhans/metabolism , Potassium Channels, Inwardly Rectifying , Potassium Channels/metabolism , Sulfonylurea Compounds/metabolism , Adenosine Diphosphate/pharmacology , Adenosine Triphosphate/antagonists & inhibitors , Adenosine Triphosphate/pharmacology , Animals , Electrophysiology , Guanosine Diphosphate/pharmacology , Guanosine Triphosphate/pharmacology , Hypoglycemic Agents/pharmacology , Islets of Langerhans/cytology , Islets of Langerhans/drug effects , Male , Membrane Potentials/drug effects , Phosphatidylinositol 4,5-Diphosphate/pharmacology , Potassium Channel Blockers , Rats , Rats, Inbred Lew , Receptors, Drug/metabolism , Sulfonylurea Receptors , Tolbutamide/pharmacology , Uridine Triphosphate/pharmacology
12.
Article in English | MEDLINE | ID: mdl-8401812

ABSTRACT

Spontaneously diabetic BB/Wor rats received either a syngeneic fetal pancreas transplant or adult islets. In the former, 4-8 fetal pancreases were transplanted, and in the latter, 3-5000 islets. Transplantation was performed by transferring a blood clot containing the pancreases or islets to the renal subcapsular space. Insulin therapy was undertaken postoperatively, except in one experiment with adult islets. Of the fetal pancreas transplanted BB rats, 52% became normoglycaemic, and 21% remained so throughout an observation period of 10 months. Nephrectomy caused a prompt return of diabetes. The histological appearance of the grafts transplanted to the diabetic animals closely resembled that of grafts transplanted to normal rats in a parallel series. For comparison a group of BB rats received a syngeneic transplant of isolated adult islets from WF rats or BBW rats. Following adult islet transplantation, 5 out of 6 animals became hyperglycaemic after a median of 20.5 days when no insulin was given post-transplantation. Four out of 5 animals became hyperglycaemic after a median of 23 days when supportive insulin therapy was administered after the transplantation. The results indicate that recurrent diabetes is not inevitable following syngeneic fetal pancreas transplantation to spontaneously diabetic BB rats. Recurrent diabetes was only occasionally associated with mononuclear cell infiltration. Transplanted tissue was well-preserved and vascularized; mega-islets were a constant finding.


Subject(s)
Diabetes Mellitus, Type 1/surgery , Fetal Tissue Transplantation/physiology , Pancreas Transplantation/physiology , Transplantation, Heterotopic , Animals , Diabetes Mellitus, Type 1/physiopathology , Immunohistochemistry , Islets of Langerhans Transplantation/physiology , Kidney , Rats , Rats, Inbred BB , Rats, Inbred WF , Transplantation, Isogeneic
13.
Diabetes Res ; 15(4): 157-63, 1990 Dec.
Article in English | MEDLINE | ID: mdl-2132404

ABSTRACT

The present study was undertaken to determine whether the transplantation of encapsulated MHC identical islets into diabetic BB/Wor/BB rats could cure their diabetes. Islets were isolated from diabetes-resistant BB/Wor/WB rats and encapsulated in alginate-polylysine-alginate membranes. Five thousand islets were transplanted into the peritoneal cavity of spontaneously diabetic BB/Wor/BB rats (n = 9) that had been insulin dependent for more than five weeks. Similar diabetic animals were transplanted with 5,000 unencapsulated islets (n = 10) or with empty capsules (n = 3). After transplantation of free islets, the animals reverted to the insulin-dependent state after a median of 16 days (17 +/- 4 days, mean +/- SEM). After transplantation of encapsulated islets, the animals reverted to the diabetic state after a median of 59 days (54 +/- 10 days, mean +/- SEM). Light microscopic and electron microscopic analyses of capsules recovered from the peritoneal cavity after failure of graft function showed no evidence either of lymphocytic invasion of the capsules or of specific destruction of the islets. The capsules were, however, overgrown by a layer of histiocytes and numerous layers of fibroblasts. Empty capsules recovered after 15 and 60 days were overgrown to the same extent.


Subject(s)
Diabetes Mellitus, Experimental/surgery , Islets of Langerhans Transplantation/physiology , Alginates , Animals , Biocompatible Materials , Blood Glucose/metabolism , Cells, Cultured , Diabetes Mellitus, Experimental/blood , Islets of Langerhans/cytology , Islets of Langerhans Transplantation/methods , Islets of Langerhans Transplantation/pathology , Membranes, Artificial , Polylysine/analogs & derivatives , Rats , Rats, Inbred BB
14.
J Endocrinol ; 126(1): 43-9, 1990 Jul.
Article in English | MEDLINE | ID: mdl-1696304

ABSTRACT

Since porcine islets are considered a likely tissue source for islet transplantation we have studied the insulin secretory responses to stimuli and some of the cell surface antigen characteristics of porcine islet cells. In a static incubation system, the threshold level of glucose required for the stimulation of insulin secretion from freshly isolated porcine islets was found to be between 2.8 and 4.2 mmol glucose/l. Arginine (5 mmol/l) and 3-isobutyl-l-methylxanthine (1 mmol/l) potentiated insulin release induced by 8.3 mmol glucose/l. Leucine (5 mmol/l) initiated release in the presence of 2 mmol glucose/l. Neither beta-hydroxybutyrate (10 mmol/l) nor octanoate (5 mmol/l) potentiated insulin release induced by 8.3 mmol glucose/l, but beta-hydroxybutyrate initiated release in the presence of 2 mmol glucose/l while octanoate did not. A 125I-labelled protein A binding assay and an enzyme-linked immunosorbent assay system were used to detect antibody binding to islet and non-islet cells. Monoclonal antibodies raised against intact rat islets were shown to bind to both porcine and rat islet cells but not to rat hepatoma tissue culture cells or rat insulinoma cells. The serum from recently diagnosed type I diabetics was shown to bind to rat islet cells in a 125I-labelled protein A binding assay, while serum from control subjects showed little, if any, binding. Porcine islet cells were unable to distinguish between the sera of recently diagnosed type I diabetics and controls in a similar assay. In conclusion, porcine islets respond to many of the major insulin secretagogues to which human islets are sensitive.(ABSTRACT TRUNCATED AT 250 WORDS)


Subject(s)
Insulin/metabolism , Islets of Langerhans/metabolism , 1-Methyl-3-isobutylxanthine/pharmacology , 3-Hydroxybutyric Acid , Animals , Antigens, Surface/analysis , Arginine/pharmacology , Caprylates/pharmacology , Glucose/pharmacology , Hydroxybutyrates/pharmacology , In Vitro Techniques , Insulin Secretion , Islets of Langerhans/immunology , Leucine/pharmacology , Stimulation, Chemical , Swine
15.
Horm Metab Res ; 21(11): 590-5, 1989 Nov.
Article in English | MEDLINE | ID: mdl-2480322

ABSTRACT

Porcine islets were isolated by infusion of a warm collagenase solution into whole pancreata followed by static incubation at 37 degrees C for 15 minutes. The pancreata were then chopped into small pieces and the free islets purified by filtration and centrifugation over a ficoll gradient. The insulin:amylase ratio of the islets compared to that in the intact pancreas was determined in 19 pancreata and indicates that the isolated islets were of a high degree of purity. The distribution of insulin, glucagon, somatostatin and pancreatic polypeptide containing cells in pig pancreas sections was compared with that in rat. Porcine islets were much smaller and less well defined than rat islets with infiltration of acinar material even into the islet core. The levels of insulin, glucagon and somatostatin in porcine pancreas and isolated porcine islets were measured using conventional radioimmunoassay techniques. The ratio of these hormones in the pancreas was 105.1:5.8:1 respectively, and in the islets 105.1:0.68:0.087 respectively. Fragmentation of the islets during the isolation may have led to the loss of glucagon and somatostatin-containing cells. Islets cultured overnight and tested with a range of glucose concentrations for one hour did not show a significant stimulation of insulin secretion in the presence of 8.3 mM or 16.7 mM glucose compared to that in 2.8 mM glucose. However freshly isolated islets challenged with 8.3 mM, 13.9 mM and 22.2 mM glucose showed a 1.8 fold, 2.0 fold and 2.3 fold response respectively, over that in 2.8 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)


Subject(s)
Islets of Langerhans/metabolism , Amylases/metabolism , Animals , Culture Techniques , Glucagon/metabolism , Glucose/pharmacology , Immunoenzyme Techniques , Insulin/metabolism , Insulin Secretion , Islets of Langerhans/cytology , Pancreas/enzymology , Rats , Somatostatin/metabolism , Swine
16.
Diabetologia ; 28(12): 933-5, 1985 Dec.
Article in English | MEDLINE | ID: mdl-4092862

ABSTRACT

A group of 36 diabetes-prone BB Wistar rats were given prophylactic insulin treatment with heat-treated bovine ultralente insulin (15 IU X kg-1 X day-1) from 50 to 142 days of age. The incidence of Type 1 (insulin-dependent) diabetes at the end of the treatment period was compared to that of 36 control animals given insulin only from the first day of glycosuria. At withdrawal of the prophylactic insulin treatment, 6 of 36 treated animals were insulin-dependent, while 15 of 36 control animals had developed diabetes (p less than 0.02). One control animal (day 153) and 2 insulin-treated animals (day 172 and 186) subsequently developed diabetes, yielding an overall diabetes incidence of 16 of 36 controls against 8 of 36 insulin treated (p less than 0.05). The finding that prophylactic insulin treatment of diabetes-prone BB Wistar rats reduced the incidence of diabetes suggests a relationship of the immune destruction of B cells to the endogenous insulin production/secretion rate.


Subject(s)
Diabetes Mellitus, Experimental/genetics , Insulin, Long-Acting/therapeutic use , Animals , Cattle , Crosses, Genetic , Diabetes Mellitus, Experimental/prevention & control , Female , Humans , Male , Rats , Rats, Inbred Strains , Time Factors
17.
Biochem Pharmacol ; 32(22): 3381-7, 1983 Nov 15.
Article in English | MEDLINE | ID: mdl-6651862

ABSTRACT

Small unilamellar liposomes containing bovine serum albumin were prepared by a new double-emulsion technique and administered to mice and rats in intravenous injections. The elimination of intact liposomes, the association of phospholipid marker with lipoproteins, and the appearance of released internal marker and its degradation products were followed by column chromatography of plasma samples. In vitro labelled lipoproteins were administered to the animals in intravenous injections together with free bovine serum albumin and the elimination of the two substances was studied by closely related techniques. The clearance of intact PC:PS (4:1) liposomes from plasma was biphasic and much faster than that of labelled lipoproteins and bovine serum albumin either originating from liposomes or injected as such. The second elimination phase for these liposomes was barely detectable by our analytical methods. In contrast, DSPC:CHOL (2:1) liposomes showed a very significant second-phase elimination, with a half-life of 12 hr for the intact liposomes. In tissue distribution studies in mice, the major accumulation of liposomal markers was found in the liver and spleen, and less in the kidneys and intestinal wall. Uptake into liver and spleen appeared to be due to the uptake of intact liposomes, whereas the uptake into kidneys and gut wall was caused by the uptake of liposomal degradation products. The uptake of PC:PS (4:1) liposomes into the liver was higher than that of DSPC:CHOL (2:1) liposomes; the opposite was the case with their uptake into the spleen. In rats, too, liposomes of different compositions showed significant variations in stability and in plasma half-lives of intact liposomes. Generally, there was a considerable increase in the liposomal stability in the presence of cholesterol and when use was made of a phospholipid with a high transition temperature.


Subject(s)
Liposomes/metabolism , Animals , Cholesterol/blood , Drug Stability , Female , Half-Life , Injections, Intravenous , Kinetics , Lipoproteins, HDL/blood , Liposomes/administration & dosage , Male , Mice , Phospholipids/blood , Rats , Serum Albumin, Bovine/administration & dosage , Serum Albumin, Bovine/metabolism , Tissue Distribution
18.
Biochem Pharmacol ; 32(22): 3389-96, 1983 Nov 15.
Article in English | MEDLINE | ID: mdl-6651863

ABSTRACT

Small solid liposomes made from distearoylphosphatidyl choline and cholesterol (molar ratio 2:1) showed significant stability in plasma, with a half-life of about 24 hr after intravenous injection in rats. The major cellular uptake of intact liposomes was found in the liver and spleen, peaking after 2-4 hr in the liver and after 24 hr in the spleen. Isolation of parenchymal and non-parenchymal cells from rat livers at various intervals after injection of liposomes showed that both cell types adsorbed liposomal membranes and took up the liposomal contents. Our study has shown that most of the liposomal markers found in the liver shortly (less than 40 min) after administration stemmed from the liposomes adsorbed to extracellular binding sites, and that uptake into the cells took place subsequently. In non-parenchymal cells, uptake was rapid and the intracellular level remained rather constant after 40 min and for up to 4 hr. The uptake of liposomes by parenchymal cells was slower, it showed a lag-phase of approx. 1/2 hr and peaked at 2 hr, whereupon the radioactivity in parenchymal cells dropped. The contents of liposomes behaved in a manner similar to the membranes. It is concluded that, in addition to a rapid uptake of liposomes in non-parenchymal liver cells, there is a significant degree of association with parenchymal cells, provided that the liposomes administered are small (less than 100 nm in diameter) and stable.


Subject(s)
Liposomes/metabolism , Liver/metabolism , Animals , Cholesterol/metabolism , Kinetics , Male , Particle Size , Phosphatidylcholines/metabolism , Rats , Rats, Inbred Strains , Serum Albumin, Bovine/metabolism , Spleen/metabolism , Tissue Distribution
19.
Diabetologia ; 12(4): 339-42, 1976 Aug.
Article in English | MEDLINE | ID: mdl-134920

ABSTRACT

In the isolated perfused rat pancreas various sulfonylurea drugs were tested with a basal glucose level of 1 mg/ml in the perfusion buffer and were found to cause a biphasic insulin response. NOVOCS 476, a new and potent sulfonylurea, and glibenclamide qualitatively differed from tolbutamide, glibornuride, glipizide, and glisoxepide, which were all alike in terms of the relationship between first and second phases of insulin release.


Subject(s)
Insulin/metabolism , Islets of Langerhans/drug effects , Sulfonylurea Compounds/pharmacology , Animals , Glipizide/pharmacology , Glyburide/pharmacology , In Vitro Techniques , Insulin Secretion , Islets of Langerhans/metabolism , Male , Perfusion , Rats , Tolbutamide/pharmacology
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