Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-08-23Bitstream added on 2014-06-13T18:41:36Z : No. of bitstreams: 1 luvizotto_ram_dr_botfm.pdf: 1198793 bytes, checksum: 382632d84e62659b419cf0c7556d0905 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Obesidade, uma alteração do estado nutricional, é definida como um acúmulo excessivo ou anormal de tecido adiposo que pode deteriorar a saúde. O tecido adiposo participa ativamente na regulação de energia corporal. As células adiposas produzem várias substâncias biologicamente ativas, as adipocinas, com diferentes funções fisiológicas. A disfunção dos adipócitos, como ocorre na obesidade, pode alterar a liberação de adipocinas, como leptina, resistina e adiponectina. A restrição calórica afeta a regulação da expressão gênica do tecido adiposo, normalizando as alterações das adipocinas causadas pela obesidade; entretanto, este mecanismo ainda é pouco conhecido. Sabe-se que resistina, adiponectina, leptina e hormônios tireoidianos estão envolvidos na regulação do balanço energético. Entretanto, não é bem estabelecido os efeitos do hipertireoidismo sobre as adipocinas em ratos obesos e obesos submetidos à restrição calórica. O objetivo deste estudo foi analisar a influência de diferentes doses de triiodotironina (T3) sobre a concentração sérica e expressão gênica de leptina, resistina e adiponectina em animais obesos e obesos submetidos à restrição calórica. Para isto, foram utilizados ratos Wistar machos separados inicialmente em controle (C) e obeso (OB). Os animais C receberam dieta padrão e os OB receberam dieta hipercalórica por 20 semanas. Após o período de indução de obesidade, os animais OB foram randomizados em grupo obeso (OB), obeso com dose de 5 μg de T3/100g de peso do animal (OS1), obeso com dose de 25 μg de T3/100g de peso do animal (OS2), obeso submetido à restrição calórica (RC), RC com dose de 5 μg de T3/100g de peso do animal (RS1) e RC com dose de 25 μg de T3/100g de peso do animal (RS2). Os grupos restritos receberam 75% do... / Obesity, an alteration of the nutritional state, is defined as an excessive or abnormal accumulation of adipose tissue that can cause health to deteriorate. Adipose tissue actively participates in the regulation of bodily energy. Adipose cells produce several biologically active substances, including adipokines, with different physiological functions. Dysfunction of adipocytes, as occurs in obesity, can alter the release of adipokines such as leptin, resistin and adiponectin. Calorie restriction affects the regulation of gene expression of adipose tissue, normalizing the alterations of adipokines caused by obesity; however, this mechanism remains poorly understood. It is known that resistin, adiponectin, leptin and thyroidal hormones are involved in the regulation of energetic balance. However, the effects of hyperthyroidism on adipokines in obese rats, submitted and not submitted to calorie restriction, are not well established. The present study aimed to analyze the influence of different doses of triiodothyronine (T3) on the serum concentration and gene expression of leptin, resistin and adiponectin in obese animals, submitted and not submitted to calorie restriction. Were used male Wistar rats initially separated into control (C) and obese (OB) groups. The C animals received control diet while OB received hypercaloric diet for 20 weeks. After the obesity-induction period the OB animals were randomly divided into obese (OB), obese with 5 μg dose of T3/100g animal body weight (OS1), obese with 25 μg dose of T3/100g body weight (OS2), obese submitted to calorie restriction (CR), CR with 5 μg dose of T3/100g body weight (RS1) and CR with 25 μg does of T3/100g body weight (RS2). The restricted groups received 75% of control group food consumption for 8 weeks. After this period, animals OS1, OS2, RS1 and ... (Complete abstract click electronic access below)

Relatively few studies have examined the effects of psychostimulants in obese subjects. Using the dietary obese rat model, the present experiments determined the reductions in food intake (hypophagia) and increases in locomotion (hyperlocomotion) induced by cocaine in diet-induced obese prone (DIO-prone) rats and diet resistant prone (DR-prone) rats as well as diet-induced obese (DIO) rats and diet resistant (DR) rats. In Experiment 1, thirty-six male Sprague-Dawley rats were given intra-peritoneal (i.p.) injections of cocaine (0, 10, 20, and 30 mg/kg) immediately prior to placement into locomotor chambers outfitted with a food source and a water source for a 60-minute test period. In Experiment 2, the same rats were exposed to a high-fat diet, and were subsequently divided into groups according to the extent of the weight gain (high weight gainers œ DIO group, low weight gainers œ DR group, and residual weight gainers œ MIX group). The rats were retested for reactivity to cocaine using conditions similar to those in Experiment 1. Rats injected with cocaine prior to high-fat exposure (Experiment 1) showed a dose dependent suppression of food intake, as well as a dose dependent increase in locomotor activity, with DR-prone rats exhibiting an enhanced degree of cocaine-induced hypophagia, as well as cocaine-induced hyperlocomotion as compared to the other groups. In Experiment 2, DIO rats exhibited a suppression of food intake after injection of 10 mg/kg cocaine, as well as an increase in locomotor activity that was significantly greater than noted in the other groups. When the results of Experiment 1 were analyzed as a function of prospective body weight gain (as opposed to placement into distinct groups), reactivity to cocaine decreased as body weight gain increased. In contrast, after high-fat exposure and weight gain, increased body weight gain was associated with an increased magnitude of suppression in food intake after cocaine administration. Similar patterns of differential cocaine sensitivity were observed for cocaine hyperlocomotion in Experiment 2. These studies indicate that although the propensity to develop obesity is associated with a diminished cocaine response, cocaine reactivity is enhanced after the induction of obesity.

Relatively few studies have examined the effects of psychostimulants in obese subjects. Using the dietary obese rat model, the present experiments determined the reductions in food intake (hypophagia) and increases in locomotion (hyperlocomotion) induced by cocaine in diet-induced obese prone (DIO-prone) rats and diet resistant prone (DR-prone) rats as well as diet-induced obese (DIO) rats and diet resistant (DR) rats. In Experiment 1, thirty-six male Sprague-Dawley rats were given intra-peritoneal (i.p.) injections of cocaine (0, 10, 20, and 30 mg/kg) immediately prior to placement into locomotor chambers outfitted with a food source and a water source for a 60-minute test period. In Experiment 2, the same rats were exposed to a high-fat diet, and were subsequently divided into groups according to the extent of the weight gain (high weight gainers œ DIO group, low weight gainers œ DR group, and residual weight gainers œ MIX group). The rats were retested for reactivity to cocaine using conditions similar to those in Experiment 1. Rats injected with cocaine prior to high-fat exposure (Experiment 1) showed a dose dependent suppression of food intake, as well as a dose dependent increase in locomotor activity, with DR-prone rats exhibiting an enhanced degree of cocaine-induced hypophagia, as well as cocaine-induced hyperlocomotion as compared to the other groups. In Experiment 2, DIO rats exhibited a suppression of food intake after injection of 10 mg/kg cocaine, as well as an increase in locomotor activity that was significantly greater than noted in the other groups. When the results of Experiment 1 were analyzed as a function of prospective body weight gain (as opposed to placement into distinct groups), reactivity to cocaine decreased as body weight gain increased. In contrast, after high-fat exposure and weight gain, increased body weight gain was associated with an increased magnitude of suppression in food intake after cocaine administration. Similar patterns of differential cocaine sensitivity were observed for cocaine hyperlocomotion in Experiment 2. These studies indicate that although the propensity to develop obesity is associated with a diminished cocaine response, cocaine reactivity is enhanced after the induction of obesity.

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Thesis (MScMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Introduction: Obesity and its associated complications, such as the metabolic syndrome, hypertension and cardiovascular disease, are escalating worldwide. In recognition of this, untested remedies advertised as anti-diabetic agents are flooding the market. Many of these products have limited efficacy, limited tolerability and significant side-effects. One remedy, claiming to have anti-diabetic properties, is DiaviteTM. DiaviteTM, a herbal product, consisting solely of the dried and ground pods of the Prosopis glandulosa tree, which is currently marketed as a food supplement with blood glucose and blood pressure stabilizing properties, as well as having the ability to enhance glucose utilization. It is already freely available from agents as well as sold over the counter at pharmacies. The producers of DiaviteTM are now seeking registration for their product from the Medicines Control Council (MCC) and, therefore, require solid scientific evidence of its effects. Aims: The aims of our study were, on request of the producing company, to determine the efficacy of DiaviteTM (P. glandulosa) as an anti-diabetic agent and possible mechanisms of action of this plant product. Methology: We utilized rat models of streptozotocin (STZ)-induced type 1 diabetes and diet-induced obese (DIO) insulin resistance. Male Wistar rats were rendered (a) type 1 diabetic after a once-off intra-peritoneal injection of STZ at a dose of 40 mg/kg and (b) insulin resistant after being on a high caloric diet (DIO) for 16 weeks. Half the animals of the type 1 diabetes model as well as the insulin resistant model were placed on DiaviteTM treatment (25 mg/kg/day) for a period of 4 – 8 weeks, depending on the model. The STZ-induced type 1 diabetic rats were sacrificed and the pancreata harvested for histological analysis. Animals on the DIO diet were sacrificed and (i) intra-peritoneal fat weight determined (ii) isolated hearts subjected to ischaemia/reperfusion to determine infarct size and protein expression profiles and (iii) cardiomyocytes prepared to determine insulin sensitivity. At the time of sacrifice blood was collected for blood glucose and serum insulin level determination, for both models. In addition, a standard toxicology study was performed in Vervet monkeys over a 3 month period. Results: In our type 1 diabetic model (blood glucose > 10 mmol/L) with a β-cell reserve, DiaviteTM treatment lead to increased serum insulin levels (p < 0.001) in both control and STZ groups as well as increased small β-cell (0 - 2500 μm2) formation (p < 0.001) in the pancreas of the STZ animals. Hearts from DiaviteTM treated control and DIO insulin resistant animals presented with smaller infarct sizes (p < 0.05) after ischaemia/reperfusion compared to their controls. DiaviteTM treatment lead to the increase of basal (p < 0.01) and insulin-stimulated (p < 0.05) glucose uptake in cardiomyocytes prepared from DIO insulin resistant animals. DiaviteTM treatment also led to significantly suppressed PTEN expression and activity (p < 0.01) in the DIO insulin resistant animals. In addition, DiaviteTM treatment had (i) no obvious detrimental effects in our rat models and (ii) no toxicity over a 3 month period in vervet monkeys. Conclusion: Our present study has shown that DiaviteTM treatment lowers fasting blood glucose levels, stimulates insulin secretion and leads to the formation of β-cells. In addition, oral consumption of DiaviteTM elicits cardioprotection against an ischaemic incident. DiaviteTM treatment improves insulin sensitivity of cardiomyocytes. Furthermore, it has been established that DiaviteTM treatment has no obvious detrimental effects in either of our rat models and no short-term toxic effects over a 3 month period in Vervet monkeys (data not shown). We thus conclude that in our models, DiaviteTM proved safe and it seems as if DiaviteTM, after short-term use, is beneficial as a dietary supplement. / AFRIKAANSE OPSOMMING: Inleiding: Vetsug, en die gepaardgaande komplikasies, soos die metaboliese sindroom, hipertensie en kardiovaskulêre siektes, neem wêreldwyd toe. Daar is tans verskeie middels op die mark wat as anti-diabetiese middels geadverteer word. Baie van hierdie geadverteerde produkte het beperkte effektiwiteit en het verskeie newe-effekte. Een so ‘n middel, is DiaviteTM. DiaviteTM is 'n plantproduk, wat slegs uit die gedroogte en fyngemaakte peule van die P. glandulosa boom bestaan. Hierdie produk word tans bemark as 'n voedselaanvulling met beide bloedglukose en bloeddruk stabiliserende eienskappe, asook die vermoë om glukose gebruik te verbeter. DiaviteTM is reeds vrylik beskikbaar van agente sowel as verkrygbaar by verskeie apteke. Die produsente van DiaviteTM wil aansoek doen om registrasie vir hul produk by die Medisynebeheerraad (MCC) en hulle vereis daarom wetenskaplike bewyse van die gevolge van die gebruik van hierdie produk. Doel: Die doel van ons studie was om op versoek van die produksie maatskappy, die doeltreffendheid van DiaviteTM (P. glandulosa) as 'n anti-diabetiese behandeling te evalueer, sowel as die moontlike meganismes van werking van hierdie plantproduk. Metodes: Ons het gebruik gemaak van rot modelle van (i) streptozotocin (STZ)-geïnduseerde tipe 1 diabetes en (ii) dieet-geïnduseerde vetsugtig (DIO) insulienweerstandigheid. Manlike Wistar rotte was as (a) tipe 1 diabeties geklassifiseer na 'n eenmalige, intra-peritoneale inspuiting van STZ teen 'n dosis van 40 mg/kg en as (b) insulienweerstandig geklassifiseer, nadat hulle op 'n hoë kalorie dieet (DIO) vir 16 weke was. Die helfte van beide die tipe 1 diabetes en die insulienweerstandige groep diere was met DiaviteTM behandel (25 mg/kg/dag) vir 'n tydperk van 4 - 8 weke, afhangende van die model. Die STZ-geïnduseerde tipe 1 diabetes rotte is geslag en die pankreata geoes vir histologiese analise. Diere op die DIO dieet is geslag en (i) die intra-peritoneale vet gewig bepaal, (ii) die geïsoleerde harte blootgestel aan isgemie/herperfusie om die infarkt groottes vas te stel, sowel as die proteïenuitdrukkingsprofiele te bepaal en (iii) kardiomiosiete was berei om die insulien sensitiwiteit te bepaal. Ten tyde van die slagting is bloedmonsters geneem vir bloedglukose en serum insulien vlak bepaling, vir beide modelle. Additioneel, is 'n standaard toksologie studie met Vervet apies oor 'n 3 maande tydperk uitgevoer. Resultate: In die model van tipe 1 diabetes (bloed glukose > 10 mmol/L), met 'n β-sel reserwe, is gevind dat DiaviteTM behandeling tot verhoogde serum insulien vlakke (p < 0.001) in beide kontrole en STZ groepe lei. DiaviteTM behandeling lei ook tot ‘n hoër vlak van klein β-sel (0 - 2500 μm2) vorming (p < 0.001) in die pankreas van die STZ diere. Die harte van die DiaviteTM behandele kontrole en DIO groep het kleiner infarkt groottes (p < 0.05) getoon na isgemie/herperfusie in vergelyking met hul kontrole groepe. DiaviteTM behandeling het ook gelei tot verhoogde basal (p < 0. 01) en insulin-gestimuleerde (p < 0. 05) glukose opname in kardiomiosiete wat berei was van DIO insulinweerstandige diere. DiaviteTM behandeling het PTEN uitdrukking en aktiwiteit aansienlik onderdruk (p < 0.01) in die DIO insulienweerstandige groep diere. Daar is dus gevind dat DiaviteTM behandeling (i) geen duidelike nadelige invloed in ons rot-modelle en (ii) geen toksisiteit oor 'n 3 maande tydperk in Vervet apies getoon nie. Gevolgtrekking: Ons huidige studie toon dus dat DiaviteTM behandeling vastende bloedglukosevlakke verlaag, insulien sekresie stimuleer en die proses van β-sell vorming bevorder. Additioneel, is gewys dat wanneer DiaviteTM mondelings gebruik word, dit die hart beskerm teen isgemiese insidente. Ons het ook getoon dat DiaviteTM behandeling insuliensensitiwiteit van kardiomiosiete verhoog. Verder is daar vasgestel dat DiaviteTM behandeling geen ooglopende nadelige gevolge in beide ons rot-modelle getoon het nie en daar geen korttermyn-toksiese effekte oor 'n 3 maande tydperk in Vervet apies (data nie getoon) is nie. Ons kan dus aflei dat Diavite TM in ons modelle veilig is en na kort termyn gebruik, voordelig is as 'n dieetaanvulling.

Submitted in fulfillment of the requirement for the degree of Doctor of Philosophy in the Faculty of Health Sciences at the University of the Witwatersrand, Johannesburg / Renewed interest in cannabinoid compounds arose since the discovery of the endocannabinoid system in the early 1990’s and its role in mediating the body’s energy balance. The aim of this study was to investigate the effect of an organic Cannabis sativa (hereafter referred to as C. sativa) extract on β-cell secretory function using an in vivo diet-induced obese rat model and an in vitro isolated rat pancreatic islet model and to determine the associated molecular changes within the pancreatic tissue. Materials and methods: Diet-induced obese Wistar rats and rats fed on standard pellets were subcutaneously injected, over a 28 day period, with an organic C. sativa extract or the vehicle (1% Tween 80® in saline). The effect of diet and treatment was evaluated using the intraperitoneal glucose tolerance tests (IPGTTs) and quantitative polymerase chain reaction (qPCR) analysis on rat pancreata. In vitro studies were conducted using isolated rat islets exposed to 11.1 (representative of normoglycemic conditions) and 33.3 mM glucose levels (representative of hyperglycemic conditions) over a 24-(D1; acute) and 96-hour (D4; chronic) period, and treated with C. sativa extract containing an equivalent of 2.5 (T1) and 5 ng/mL (T2) tetrahydrocannabinol (THC). Glucose-stimulated insulin secretion (GSIS), immunohistocytochemistry for apoptosis and proliferation detection and western blotting for detection of cannabinoid receptor type 1 (CB1), CB2 receptors and specific transduction factors were undertaken. Antagonist studies were conducted using AM251 (A1) and AM630 (A2) to block CB1 and CB2, respectively, to determine the role of cannabinoid receptors in insulin secretion. Results: The overall increase in body weight in the experimental groups occurred at a significantly slower rate than the control groups (P < 0.01), irrespective of diet. In the lean group, the area under the curve for glucose (AUCg) was significantly higher compared to the diet-induced obese group (P < 0.001), while C. sativa treatment significantly improved the AUCg in the lean rats (P < 0.05). The cafeteria diet did not induce hyperglycemia and insulin resistance in the obese rats and C. sativa treatment maintained a plasma glycemic profile similar to the obese control rats. The lower AUCg values in the obese group may, in part, be due to the inclusion of milk products (shown to be beneficial in reducing diabetes) in the cafeteria diet. qPCR analysis showed that the cafeteria diet induced down-regulation of the following genes in the obese control group, relative to lean controls: UCP2 (P < 0.01), c-MYC (P < 0.05) and FLIP (P < 0.05), and upregulation of CB1 (P < 0.01), GLUT2 (P < 0.001), UCP2 (P < 0.001) and PKB (P < 0.05), relative to the obese control group, while c-MYC levels were down-regulated (P < 0.05), relative to the lean control group. In the in vitro study, results showed C. sativa treatment decreased chronic insulin secretion in islets cultured under normoglycemic condition for D1 (P < 0.05), but not for D4. In islets cultured under hyperglycemic conditions, C. sativa treatment for the D4 period showed a significant increase in their chronic insulin secretion (HD4T1, P = 0.07; HD4T2, P < 0.001), increase in basal insulin secretion (HD4T1, P < 0.001; HD4T2, P < 0.001), increase in GSIS (HD4T1, P < 0.05; HD4T2, P < 0.001), reduction in glucose-stimulated:basal insulin production (HD4T1, P < 0.05; HD4T2, P < 0.05), reduction in insulin content (HD4T1, P < 0.001), increase in the percentage basal : content ratio (HD4T1, P < 0.001; HD4T2, P < 0.01) and increase in the percentage GSIS : content ratio (HD4T1, P < 0.001; HD4T2, P < 0.05), relative to ND4C islets. In antagonist studies, A2 preconditioning did not affect suppress the stimulatory effect of C. sativa treatment on chronic insulin secretion under normo- and hyperglycemic conditions, relative to the NC and HC islets, respectively. qPCR studies showed that C. sativa exposure induced a 2.2-fold increase in CB1 gene expression, relative to normoglycemic control islets (P < 0.05), while c-MYC and FLIP expression was significantly reduced by 12% (ND4T1, P < 0.05) and 37% (HD4T1, P < 0.05), respectively. C. sativa treatment also induced increased secretion of anti-inflammatory cytokines/chemokines under hyperglycemic conditions. Conclusion: These results suggest that C. sativa protects pancreatic islets against the negative effects of obesity (in vivo studies) and hyperglycemia (in vitro studies). In light of these findings, further investigation into the potential of C. sativa as a complementary therapeutic agent in the treatment of the deleterious effects of hyperglycemia in diabetic patients is warranted. In addition, the significant effect of C. sativa treatment on adipose tissue in experimental rats needs further investigation to determine how the cannabinoids affect the mechanisms of adipogenesis and lipolysis in diet-induced obesity. Keywords: Diet-Induced Obesity, Cannabinoids, C. sativa, THC, β-cell, AM251, AM630.

Orientador: Célia Regina Nogueira / Banca: Gláucia Maria Ferreira da Silva Mazeto. / Banca: Vânia dos Santos Nunes / Banca: Magnus R. D. Silva / Banca: Christiane Y. M. N. N. Coimbra / Resumo: Obesidade, uma alteração do estado nutricional, é definida como um acúmulo excessivo ou anormal de tecido adiposo que pode deteriorar a saúde. O tecido adiposo participa ativamente na regulação de energia corporal. As células adiposas produzem várias substâncias biologicamente ativas, as adipocinas, com diferentes funções fisiológicas. A disfunção dos adipócitos, como ocorre na obesidade, pode alterar a liberação de adipocinas, como leptina, resistina e adiponectina. A restrição calórica afeta a regulação da expressão gênica do tecido adiposo, normalizando as alterações das adipocinas causadas pela obesidade; entretanto, este mecanismo ainda é pouco conhecido. Sabe-se que resistina, adiponectina, leptina e hormônios tireoidianos estão envolvidos na regulação do balanço energético. Entretanto, não é bem estabelecido os efeitos do hipertireoidismo sobre as adipocinas em ratos obesos e obesos submetidos à restrição calórica. O objetivo deste estudo foi analisar a influência de diferentes doses de triiodotironina (T3) sobre a concentração sérica e expressão gênica de leptina, resistina e adiponectina em animais obesos e obesos submetidos à restrição calórica. Para isto, foram utilizados ratos Wistar machos separados inicialmente em controle (C) e obeso (OB). Os animais C receberam dieta padrão e os OB receberam dieta hipercalórica por 20 semanas. Após o período de indução de obesidade, os animais OB foram randomizados em grupo obeso (OB), obeso com dose de 5 μg de T3/100g de peso do animal (OS1), obeso com dose de 25 μg de T3/100g de peso do animal (OS2), obeso submetido à restrição calórica (RC), RC com dose de 5 μg de T3/100g de peso do animal (RS1) e RC com dose de 25 μg de T3/100g de peso do animal (RS2). Os grupos restritos receberam 75% do ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Obesity, an alteration of the nutritional state, is defined as an excessive or abnormal accumulation of adipose tissue that can cause health to deteriorate. Adipose tissue actively participates in the regulation of bodily energy. Adipose cells produce several biologically active substances, including adipokines, with different physiological functions. Dysfunction of adipocytes, as occurs in obesity, can alter the release of adipokines such as leptin, resistin and adiponectin. Calorie restriction affects the regulation of gene expression of adipose tissue, normalizing the alterations of adipokines caused by obesity; however, this mechanism remains poorly understood. It is known that resistin, adiponectin, leptin and thyroidal hormones are involved in the regulation of energetic balance. However, the effects of hyperthyroidism on adipokines in obese rats, submitted and not submitted to calorie restriction, are not well established. The present study aimed to analyze the influence of different doses of triiodothyronine (T3) on the serum concentration and gene expression of leptin, resistin and adiponectin in obese animals, submitted and not submitted to calorie restriction. Were used male Wistar rats initially separated into control (C) and obese (OB) groups. The C animals received control diet while OB received hypercaloric diet for 20 weeks. After the obesity-induction period the OB animals were randomly divided into obese (OB), obese with 5 μg dose of T3/100g animal body weight (OS1), obese with 25 μg dose of T3/100g body weight (OS2), obese submitted to calorie restriction (CR), CR with 5 μg dose of T3/100g body weight (RS1) and CR with 25 μg does of T3/100g body weight (RS2). The restricted groups received 75% of control group food consumption for 8 weeks. After this period, animals OS1, OS2, RS1 and ... (Complete abstract click electronic access below) / Doutor

Obesity and drug abuse share common neural circuitries including the mesocoticolimbic and striatal dopamine reward system. In the current study, a rat model of diet-induced obesity (DIO) was used to determine striatal dopamine function, impulsivity and motivation as neurobehavioral outcomes and predictors of obesity. For the outcome study, rats were randomly assigned a high-fat (HF) or a low-fat (LF) diet for 8 wk. Following the 8-wk HF-diet exposure, rats were segregated into obesity-prone and obesity-resistant groups based on maximum and minimum body weight gain, respectively, and neurobehavioral outcomes were evaluated. For the predictor study, neurobehavioral antecedents were evaluated prior to an 8-wk high-fat diet exposure and were correlated with subsequent body weight gain. Striatal D2 receptor density was determined by in vitro kinetic analysis of [3H]raclopride binding. DAT function was determined using in vitro kinetic analysis of [3H]dopamine uptake, methamphetamine-evoked [3H]dopamine overflow and no net flux in vivo microdialysis. DAT cell-surface expression was determined using biotinylation and Western blotting. Impulsivity and food-motivated behavior were determined using a delay discounting task and progressive ratio schedule for food-reinforcers, respectively. Relative to obesity-resistant, obesity-prone rats exhibited 18% greater body weight, 42% lower striatal D2 receptor density, 30% lower total DAT expression, 40% lower in vitro and in vivo DAT function, 45% greater extracellular dopamine concentration, and 2-fold greater methamphetamine-evoked [3H]dopamine overflow. Obesity-prone rats exhibited higher motivation for food, but were less impulsive relative to obesity-resistant rats. Neurobehavioral antecedents of DIO included greater motivation for high-fat reinforcers in rats subsequently shown to be obesity-prone relative to obesity-resistant. Impulsivity, DAT function and extracellular dopamine concentration did not predict the DIO-phenotype. Thus, motivation for food is linked to both initiation and maintenance of obesity. Importantly, obesity results in decreased striatal DAT function, which may underlie the maintenance of compulsive food intake in obesity.

Thesis (MScMedSc)--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Obesity is a major risk factor for ischaemic heart disease. Obesity-induced metabolic abnormalities have been associated with increased oxidative stress which may play an important role in the increased susceptibility to myocardial dysfunction and ischaemiareperfusion (I/R) injury seen in obesity. The pineal gland hormone, melatonin, has powerful antioxidant properties. Previous studies have shown that short-term or acute melatonin administration protects the normal healthy heart of lean animals against I/R damage. However, the effects of melatonin on the heart in obesity remain unknown. Moreover, the myocardial signalling mechanisms associated with the cardioprotective effects of melatonin have not been established. Using a rat model of diet induced obesity, we set out to: 1) investigate the effects of chronic melatonin administration on the development of diet-induced systemic alterations including biometric and metabolic parameters and oxidative stress, 2) determine whether chronic melatonin treatment protects the myocardium against ischaemia-reperfusion injury, and 3) determine whether melatonin treatment confers cardioprotection by altering the reperfusion injury salvage kinase (RISK) pathway signalling and the pro-apoptotic p38 MAPK, AMPK and GLUT-4 expression. Male rats weighing 200±20g were randomly allocated to four groups: 1) C, control rats receiving a standard commercial rat chow and drinking water without melatonin; 2) CM, control rats receiving melatonin (4mg/kg/day) in drinking water; 3) D, diet-induced obesity rats, receiving a high calorie diet and drinking water without melatonin; 4) DM, diet-induced obesity rats, receiving melatonin in drinking water. After 16 weeks of treatment and feeding, rats were weighed and blood and myocardial tissue collected to document biochemical and molecular biological changes. Hearts were perfused on the isolated working rat heart perfusion apparatus for the evaluation of myocardial function and infarct size. The Reperfusion Injury Salvage Kinases (RISK) pathway (PKB/Akt (Ser-473), ERK p42/ p44) and p38 MAPK (mitogenactivated protein kinase) were investigated in pre-and post-ischaemic hearts using Western blotting techniques. Post-ischaemic activation of AMPK (5’AMP-activated protein kinase) (Thr- 172) and GLUT-4 (glucose transporter) expression were also investigated. Serum and baseline myocardial glutathione (GSH) content were measured. In addition, serum lipid peroxidation products: thiobarbituric reactive substances (TBARS), conjugated dienes (CD) and lipid hydroperoxide (LOOH), were also determined. The high-calorie diet caused increases in body weight, visceral adiposity, heart weight, serum insulin, leptin, blood triglycerides, and low HDL-cholesterol levels. Blood glucose levels were similar for both diet fed rats and controls. Myocardial glutathione, serum glutathione, total cholesterol, TBARS, LOOH, CD as well as total cholesterol (TC) levels were not affected by the high calorie diet. Chronic melatonin treatment reduced body weight gain, visceral adiposity, heart weight, blood triglycerides, serum insulin, HOMA index, serum leptin (DM vs D, p<0.01), and increased blood HDL-C in diet treated rats while there was no effect on these parameters in control rats, despite the reduction in body weight, heart weight and visceral adiposity. Melatonin treatment had no effect on myocardial or serum GSH and LOOH in either control or diet animals. It however reduced TBARS and CD in the diet and control groups, respectively. At baseline, chronic melatonin treatment caused a significant increase in phospho-PKB/total PKB ratio and a concomitant reduction in phospho-p38 MAPK/total p38 MAPK ratio of control hearts while there were no such effects on diet-induced-obesity hearts. Infarct size was significantly reduced by melatonin in both diet and control groups (DM: 16.6±2.0%; D: 38.4±2.6% (p < 0.001), and CM: 12.8±1.5%; C: 30.4±1.0%, p<0.001). After coronary artery occlusion and 30 minutes of reperfusion, melatonin increased percentage recovery of aortic output (DM: 28.5±6.5%; D: 6.2±6.2%, p<0.01), cardiac output (DM: 44.4±5.2%; D: 26.6±5.1%, p < 0.01) and total work (DM: 34.5±5.6%; D: 20.4±7.9%, p<0.05) of diet-induced obesity hearts, while having no effect on control hearts. During reperfusion, hearts from melatonin treated rats had increased activation of PKB/Akt (p<0.01), ERK42/44 (p<0.05), and reduced p38 MAPK activation (p<0.05). There was no difference in post-ischaemic activation of AMPK (Thr-172) and GLUT-4 expression in either control or diet fed rats. We successfully demonstrated that chronic melatonin treatment prevented the development of diet-induced metabolic abnormalities and improved ex vivo myocardial function. Melatonin protected the heart against ischaemia-reperfusion injury that was exacerbated in obesity. This was achieved by activation of the RISK pathway. The antioxidant properties of melatonin were involved in these cardioprotective effects. / AFRIKAANSE OPSOMMING: Vetsug of obesiteit is een van die hoof risikofaktore vir iskemiese hartsiekte. Obesiteitgeinduseerde metaboliese abnormaliteite gaan met verhoogde oksidatiewe stres gepaard wat op sy beurt ‘n belangrike rol mag speel in die miokardiale wanfunksie en verhoogde vatbaarheid vir iskemie-herperfusie (I/H) beskadiging, kenmerkend van vetsug. Melatonien, die hormoon afgeskei deur die pineaalklier, is ‘n kragtige anti-oksidant. Vorige studies het getoon dat kort-termyn of akute toediening van melatonien die normale hart van gesonde diere teen I/H beskadiging deur middel van sy anti-oksidant aksies beskerm. Die effek van melatonien op die hart in obesiteit is egter nog onbekend. Hierbenewens is die miokardiale seintransduksie meganismes geassosieer met die beskermende effekte van die hormoon nog nie ontrafel nie. ‘n Model van dieet-geinduseerde obesiteit in rotte is gebruik om die volgende te bepaal: (i) die effek van kroniese melatonientoediening op die ontwikkeling van dieet-geinduseerde sistemiese veranderinge soos biometriese en metaboliese parameters en oksidatiewe stres (ii) die effek van kroniese melatonienbehandeling op die respons van die hart op I/H beskadiging en (iii) die rol van herperfusie beskadiging op die aktivering van PKB/Akt en ERK42/44 (die sg RISK seintransduksiepad), die pro-apoptotiese p38MAPK, AMPK sowel as die uitdrukking van GLUT-4. Manlike Wistar rotte (200±20g) is ewekansig in vier groepe verdeel: (i) C, kontrole rotte wat ‘n standaard rotdieet en drinkwater sonder melatonien ontvang (ii) CM, kontrole rotte wat melatonien (4mg/kg/dag) ontvang (iii) D, dieet-geϊnduseerde vet rotte wat ‘n hoë kalorie dieet en drinkwater sonder melatonien ontvang (iv) DM, dieet-geϊnduseerde vet rotte wat melatonien (4mg/kg/dag) in die drinkwater ontvang. Na 16 weke van behandeling, is die rotte geweeg, bloed en hartweefsel gekollekteer vir biochemiese en molekulêre biologie bepalings. Harte is geperfuseer volgens die werkhartmodel, blootgestel aan iskemie/herperfusie vir evaluering van funksionele herstel en infarktgrootte. Uitdrukking en aktivering van PKB/Akt (Ser-473), ERKp42/p44 en p38MAPK van pre-en postiskemiese hartweefsel is met behulp van Western blot bepaal. Postiskemiese aktivering van AMPK (5’AMP-aktiveerde proteϊen kinase) (Thr-172) en GLUT-4 (glukose transporter) is op soortgelyke wyse bepaal. Serum en basislyn hartweefsel glutatioon (GSH) inhoud asook tiobarbituursuur reaktiewe substans (TBARS), gekonjugeerde diene (CD) en lipiedhidroperoksied (LOOH) konsentrasies is bepaal. Resultate Die hoë kalorie diet het ‘n toename in liggaamsgewig, visserale vet, hartgewig, serum insulien, leptien, plasma trigliseried en lae HDL-cholesterol vlakke teweegebring. Bloed glukosevlakke was egter dieselfde in die vet en kontrole rotte. Miokardiale glutatioon, serum glutatioon, totale cholesterol, TBARS, LOOH, CD is nie deur die dieet beinvloed nie. Chroniese melatonien behandeling het die liggaamsgewig, visserale vet, hartgewig, plasma trigliseried, serum insulien en leptien, HOMA indeks verlaag (DM vs D, p<0.05) en die HDL-cholesterol verhoog in die dieetrotte, terwyl dit geen effek op hierdie parameters in kontrole rotte gehad het nie (uitgesonderd ‘n afname in liggaamsgewig, hartgewig en visserale vet). Melatonien behandeling het geen effek op hart of serum GSH en LOOH in kontrole en vet rotte gehad nie. Dit het egter die TBARS en CD in beide vet en kontrole rotte verlaag. Chroniese melatonien toediening het ‘n beduidende toename in basislyn fosfo PKB//totale PKB ratio en ‘n afname in fosfo p38MAPK/totale p38MAPK ratio teweegebring in harte van kontrole rotte, maar soortgelyke effekte is nie in die harte van die vet rotte waargeneem nie. Infarktgrootte is beduidend deur melatonienbehandeling verlaag in beide dieet en kontrole groepe (DM: 16.6± 5.2%, D: 38.4 ±2.6% (p<0.001); CM: 12.8± 1.5%; C 30.4±1.0 (p<0.001). Na koronere arterie afbinding en 30 min van herperfusie, het melatonien die persentasie herstel van aorta omset (DM: 28.5± 6.5%; D: 6.2± 6.2%, p<0.01), kardiale omset ( DM: 44.4± 5.2%D: 26.6±5.1%, p<0.01) en totale werk (DM: 34.5 5.6%; D 20.4± 7.9%, p<0.05) in die harte van dieetrotte verbeter, terwyl dit sonder effek was in kontrole harte. Tydens herperfusie het harte van melatonienbehandelde rotte verhoogde aktivering van PKB/Akt (p<0.01) en ERKp42/p44 (p<0.05) getoon, terwyl aktivering van p38MAPK verlaag is (p<0.05). Geen verskil in postiskemiese aktivering van AMPK en GLUT-4 uitdrukking is in beide kontrole en dieetrotte waargeneem nie. Ons het daarin geslaag om aan te toon dat chroniese melatonienbehandeling die ontwikkeling van dieet-geϊnduseerde metaboliese abnormaliteite beduidend kan voorkom en ex vivo miokardiale funksie verbeter. Melatonien het ook die hart teen iskemie/herperfusie beskadiging beskerm in beide kontrole en dieetrotte. Bogenoemde veranderinge het met aktivering van PKB/Akt en ERKp42/p44 gepaard gegaan. Die anti-oksidant effekte van melatonien was heelwaarskynlik hierby betrokke.