| 1. |
- Ahrén, Bo, et al.
(författare)
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Islet adaptation in GIP receptor knockout mice
- 2019
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Ingår i: Peptides. - : Elsevier BV. - 0196-9781.
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Forskningsöversikt (refereegranskat)abstract
- Glucose-dependent insulinotropic polypeptide (GIP) receptor knockout (KO) mice are tools for studying GIP physiology. Previous results have demonstrated that these mice have impaired insulin response to oral glucose. In this study, we examined the insulin response to intravenous glucose by measuring glucose, insulin and C-peptide after intravenous glucose (0.35 g/kg) in 5-h fasted female GIP receptor KO mice and their wild-type (WT) littermates. The 1 min insulin and C-peptide responses to intravenous glucose were significantly enhanced in GIP receptor KO mice (n = 26) compared to WT mice (n = 30) as was beta cell function (area under the 50 min C-peptide curve divided by area under the 50 min curve for glucose) (P = 0.001). Beta cell function after intravenous glucose was also enhanced in GIP receptor KO mice in the presence of the glucagon-like peptide-1 receptor antagonist exendin 9 (30 nmol/kg; P = 0.007), the muscarinic antagonist atropine (5 mg/kg; P = 0.007) and the combination of the alpha-adrenoceptor antagonist yohimbine (1.4 mg/kg) and the beta-adrenoceptor antagonist propranolol (2.5 mg/kg; P = 0.042). Analysis of the regression between fasting glucose (6.8 ± 0.1 mmol/l in GIP receptor KO mice and 7.5 ± 0.2 mmol/l in WT mice, P = 0.003) and the 1 min C-peptide response to intravenous glucose showed a negative linear regression between these variables in both WT (n = 60; r = −0.425, P = 0.001) and GIP receptor KO mice (n = 56; r = −0.474, P < 0.001). We conclude that there is a beta cell adaptation in GIP receptor KO mice resulting in enhanced insulin secretion after intravenous glucose to which slight long-term reduction in circulating glucose in these mice may contribute.
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| 2. |
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| 3. |
- Omar, Bilal, et al.
(författare)
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Incretin hormone receptors are required for normal beta cell development and function in female mice
- 2016
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Ingår i: Peptides. - : Elsevier BV. - 1873-5169 .- 0196-9781. ; 79, s. 58-65
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Tidskriftsartikel (refereegranskat)abstract
- The incretin hormones, glucose dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1), potentiate insulin secretion and are responsible for the majority of insulin secretion that occurs after a meal. They may also, however, have a fundamental role in pancreatic beta cell development and function, independently of their role in potentiating insulin secretion after a meal. This has led to observations that a loss of GIP or GLP-1 action affects normal beta cell function, however each one of the incretin hormones may compensate when the action of the other is lost and therefore the overall impact of the incretin hormones on beta cell function is not known. We therefore utilized a mouse line deficient in both the GLP-1 and GIP receptor genes, the double incretin receptor knockout (DIRKO), to determine the consequences of a lifelong, complete lack of incretin hormone action on beta cell function, in vivo, in intact animals. We found that DIRKO mice displayed impaired glucose tolerance and insulin secretion in response to both oral glucose and mixed meal tolerance tests compared to wild-type mice. Assessment of beta cell function using the hyperglycemic clamp technique revealed an 80% decrease in first phase insulin response in DIRKO mice, but a normal second phase insulin secretion. A similar decline was seen when wild-type mice were given acute intravenous injection of glucose together with the GLP-1 receptor antagonist Ex9-39. Ex vivo assessments of the pancreas revealed significantly fewer islets in the pancreata of DIRKO mice despite no differences in total pancreatic mass. Insulin secretion from isolated islets of DIRKO mice was impaired to a similar extent to that seen during the hyperglycemic clamp. Insulin secretion in wild-type islets was impaired by acute treatment with Ex9-39 to a similar extent as the in vivo intravenous glucose tolerance tests. In conclusion, a loss of the action of both incretin hormones results in direct impairment of beta cell function both in vivo and in vitro in a process that appears to be independent of the intestinally secreted incretin hormones. We therefore conclude that the incretin hormones together significantly impact both beta-cell function and beta-cell development.
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| 4. |
- Tura, Andrea, et al.
(författare)
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Glucagon and insulin secretion, insulin clearance, and fasting glucose in GIP receptor and GLP-1 receptor knockout mice
- 2019
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Ingår i: American Journal of Physiology: Regulatory, Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 316:1, s. 27-37
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Tidskriftsartikel (refereegranskat)abstract
- It is not known whether GIP receptor and GLP-1 receptor knockout (KO) mice have perturbations in glucagon secretion or insulin clearance, and studies on impact on fasting glycemia have previously been inconsistent in these mice. We therefore studied glucagon secretion after oral whey protein (60 mg) and intravenous arginine (6.25 mg), insulin clearance after intravenous glucose (0.35 g/kg) and fasting glucose, insulin, and glucagon levels after standardized 5-h fasting in female GIP receptor and GLP-1 receptor KO mice and their wild-type (WT) littermates. Compared with WT controls, GIP receptor KO mice had normal glucagon responses to oral protein and intravenous arginine, except for an enhanced 1-min response to arginine, whereas glucagon levels after oral protein and intravenous arginine were enhanced in GLP-1 receptor KO mice. Furthermore, the intravenous glucose test revealed normal insulin clearance in both GIP receptor and GLP-1 receptor KO mice, whereas β-cell glucose sensitivity was enhanced in GIP receptor KO mice and reduced in GLP-1 receptor KO mice. Finally, GIP receptor KO mice had reduced fasting glucose (6.7 ± 0.1, n = 56, vs. 7.4 ± 0.1 mmol/l, n = 59, P = 0.001), whereas GLP-1 receptor KO mice had increased fasting glucose (9.1 ± 0.2, n = 44, vs. 7.7 ± 0.1 mmol/l, n = 41, P < 0.001). We therefore suggest that GIP has a limited role for glucagon secretion in mice, whereas GLP-1 is of importance for glucagon regulation, that GIP and GLP-1 are of importance for the regulation of β-cell function beyond their role as incretin hormones, and that they are both of importance for fasting glucose.
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| 5. |
- Tura, Andrea, et al.
(författare)
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Increased insulin clearance in mice with double deletion of glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide receptors
- 2018
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Ingår i: American Journal of Physiology - Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 314:5, s. 639-646
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Tidskriftsartikel (refereegranskat)abstract
- To establish whether incretin hormones affect insulin clearance, the aim of this study was to assess insulin clearance in mice with genetic deletion of receptors for both glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), so called double incretin receptor knockout mice (DIRKO). DIRKO (n = 31) and wild-type (WT) C57BL6J mice (n = 45) were intravenously injected with D-glucose (0.35 g/kg). Blood was sampled for 50 min and assayed for glucose, insulin, and C-peptide. Data were modeled to calculate insulin clearance; C-peptide kinetics was established after human C-peptide injection. Assessment of C-peptide kinetics revealed that C-peptide clearance was 1.66 ± 0.10 10–31/min. After intravenous glucose administration, insulin clearance during first phase insulin secretion was markedly higher in DIRKO than in WT mice (0.68 ± 0.06 10–3l/min in DIRKO mice vs. 0.54 ± 0.03 10–31/min in WT mice, P = 0.02). In contrast, there was no difference between the two groups in insulin clearance during second phase insulin secretion (P = 0.18). In conclusion, this study evaluated C-peptide kinetics in the mouse and exploited a mathematical model to estimate insulin clearance. Results showed that DIRKO mice have higher insulin clearance than WT mice, following intravenous injection of glucose. This suggests that incretin hormones reduce insulin clearance at physiological, nonstimulated levels.
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