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The impact of activation of the renin-angiotensin system in the development of insulin resistance in experimental models of obesity
Thesis (MScMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2009.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : University of Stellenbosch
2009
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| _version_ | 1867613958577324032 |
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| access_status_str | Open Access |
| author | Perel, Shireen J. C. |
| author2 | Huisamen, Barbara |
| author_browse | Huisamen, Barbara Perel, Shireen J. C. |
| author_facet | Huisamen, Barbara Perel, Shireen J. C. |
| author_sort | Perel, Shireen J. C. |
| collection | Thesis |
| dc_rights_str_mv | University of Stellenbosch |
| description | Thesis (MScMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2009. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/2664 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:44:24.894Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2009 |
| publishDateRange | 2009 |
| publishDateSort | 2009 |
| publisher | Stellenbosch : University of Stellenbosch |
| publisherStr | Stellenbosch : University of Stellenbosch |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/2664 The impact of activation of the renin-angiotensin system in the development of insulin resistance in experimental models of obesity Perel, Shireen J. C. Huisamen, Barbara University of Stellenbosch. Faculty of Health Sciences. Dept. of Biomedical Sciences. Medical Physiology. Insulin resistance -- Nitric oxide Theses -- Medicine Dissertations -- Medicine Angiotensin II Insulin resistance -- Animal models Metabolic syndrome Obesity Biomedical Sciences Medical Physiology Thesis (MScMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2009. Insulin stimulates the production of nitric oxide (NO) in endothelial cells and cardiac myocytes by a signalling pathway that involves the insulin receptor substrate (IRS)-1, phosphatidylinositol-3-kinase and protein kinase B (PKB/Akt). Physiological concentrations of NO play an important part in maintaining normal vascular function. It has been suggested that nitric oxide synthase (NOS) activity and NO production are chronically impaired in diabetes mellitus by an unknown mechanism. The reninangiotensin system and subsequent production of angiotensin II (Ang II) are elevated in obesity and diabetes while antagonism of the AT1 receptor with Losartan has beneficial effects in patients with insulin resistance and type II diabetes. Aims: We therefore aimed to investigate (i) the effect of Ang II on myocardial insulin signalling with regards to key proteins (IRS-1, PKB/Akt, eNOS and p38 MAPK) in correlation with NO production, (ii) the effect of Losartan on these parameters. Methods: Hyperphagia-induced obese, insulin resistant rats (DIO=diet supplemented with sucrose and condensed milk) were compared to age-matched controls. Half the animals were treated with 10mg/kg Losartan per day for 1 week. Isolated hearts were perfused with or without 0.03 μIU/mL insulin for 15 min. Blood glucose, bodyweight, intraperitoneal fat and plasma insulin and Ang II were recorded. Proteins of interest and their phosphorylation were determined by Western blotting. NO production was flow cytometrically analyzed. ANOVA followed by the Bonferroni correction was used with a p< 0.05 considered significant. Results: DIO animals had significant elevated bodyweight, blood glucose, plasma insulin and Ang II levels. Our data showed that the hearts from the DIO animals are insulin resistant, ultimately reflected by the attenuated activation of the key proteins (IRS-1, PKB/Akt and eNOS) involved in insulin signalling as well as NO production. AT1 receptor antagonism improved NO production in isolated adult ventricular myocytes from DIO animals while concurrently enhancing expression of eNOS, PKB/Akt and p38 MAPK. In contrast, NO production as well as expression of eNOS and PKB/Akt was attenuated in control animals after Losartan treatment. Conclusion: These results suggested that Ang II via AT1 or AT2 receptors, modulates protein expression of both PKB/Akt and eNOS. This encouraged us to investigate the involvement of AT2 receptors in the observed changes. To investigate this we needed to establish a culture of neonatal rat cardiac myocytes treated with raised fatty acids and Ang II. If similar changes were induced as observed in the hearts of DIO animals, the involvement of the AT1 and AT2 receptors could be investigated using specific antagonists against these receptors. Primary cultured ventricular myocytes were isolated from 1-3 day old Wistar rat pups. They were cultured for 48 hours before the addition of palmitate and oleate at a concentration of 0.25 mM each and were treated with or without the fatty acids for a period of 4 days. After 18 hours of serum starvation, cells were stimulated with or without 10 nM insulin for 15 minutes. The effect of fatty acid treatment on cell viability and glucose uptake were assessed by trypan blue and propidium iodide staining and 2-deoxy-D-3[H] glucose uptake respectively. Protein levels and phosphorylation of key proteins (PKB/Akt, PTEN and p38 MAPK) in insulin signalling was determined by Western blotting. 0.25 mM Fatty acids did not result in the loss of cell viability. Contrary to expectation, fatty acid treatment led to enhanced basal glucose uptake but lower Glut 1 protein expression. Basal protein expression of PPARα was, however, upregulated as was the expression of the phosphatase, PTEN. The latter could explain the lower PKB/Akt phosphorylation also documented. From these results we conclude that neonatal cardiac myocytes, cultured in the presence of elevated fatty acids, did not respond in a similar manner as the intact hearts of our animals and further modifications of the system might be needed before it can be utilized as initially planned. 2009-02-23T15:16:03Z 2010-06-01T08:54:45Z 2009-02-23T15:16:03Z 2010-06-01T08:54:45Z 2009-03 Thesis http://hdl.handle.net/10019.1/2664 en University of Stellenbosch application/pdf Stellenbosch : University of Stellenbosch |
| spellingShingle | Insulin resistance -- Nitric oxide Theses -- Medicine Dissertations -- Medicine Angiotensin II Insulin resistance -- Animal models Metabolic syndrome Obesity Biomedical Sciences Medical Physiology Perel, Shireen J. C. The impact of activation of the renin-angiotensin system in the development of insulin resistance in experimental models of obesity |
| title | The impact of activation of the renin-angiotensin system in the development of insulin resistance in experimental models of obesity |
| title_full | The impact of activation of the renin-angiotensin system in the development of insulin resistance in experimental models of obesity |
| title_fullStr | The impact of activation of the renin-angiotensin system in the development of insulin resistance in experimental models of obesity |
| title_full_unstemmed | The impact of activation of the renin-angiotensin system in the development of insulin resistance in experimental models of obesity |
| title_short | The impact of activation of the renin-angiotensin system in the development of insulin resistance in experimental models of obesity |
| title_sort | impact of activation of the renin angiotensin system in the development of insulin resistance in experimental models of obesity |
| topic | Insulin resistance -- Nitric oxide Theses -- Medicine Dissertations -- Medicine Angiotensin II Insulin resistance -- Animal models Metabolic syndrome Obesity Biomedical Sciences Medical Physiology |
| url | http://hdl.handle.net/10019.1/2664 |
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