Obesity has reached epidemic proportions worldwide and reports estimate that American children consume up to 25% of calories from snacks. Several animal models of obesity exist, but studies are lacking that compare high-fat diets (HFD) traditionally used in rodent models of diet-induced obesity (DIO) to diets consisting of food regularly consumed by humans, including high-salt, high-fat, low-fiber, energy dense foods such as cookies, chips, and processed meats. To investigate the obesogenic and inflammatory consequences of a cafeteria diet (CAF) compared to a lard-based 45% HFD in rodent models, male Wistar rats were fed HFD, CAF or chow control diets for 15 weeks. Body weight increased dramatically and remained significantly elevated in CAF-fed rats compared to all other diets. Glucose- and insulin-tolerance tests revealed that hyperinsulinemia, hyperglycemia, and glucose intolerance were exaggerated in the CAF-fed rats compared to controls and HFD-fed rats. It is well-established that macrophages infiltrate metabolic tissues at the onset of weight gain and directly contribute to inflammation, insulin resistance, and obesity. Although both high fat diets resulted in increased adiposity and hepatosteatosis, CAF-fed rats displayed remarkable inflammation in white fat, brown fat and liver compared to HFD and controls. In sum, the CAF provided a robust model of human metabolic syndrome compared to traditional lard-based HFD, creating a phenotype of exaggerated obesity with glucose intolerance and inflammation. This model provides a unique platform to study the biochemical, genomic and physiological mechanisms of obesity and obesity-related disease states that are pandemic in western civilization today.
OBJECTIVE-To characterize differences in whole-body glucose metabolism between commonly used inbred mouse strains.RESEARCH DESIGN AND METHODS-Hyperinsulinemic-euglycemic (ϳ8.5 mmol/l) and -hypoglycemic (ϳ3.0 mmol/l) clamps were done in catheterized, 5-h-fasted mice to assess insulin action and hypoglycemic counter-regulatory responsiveness. Hyperglycemic clamps (ϳ15 mmol/l) were done to assess insulin secretion and compared with results in perifused islets.RESULTS-Insulin action and hypoglycemic counter-regulatory and insulin secretory phenotypes varied considerably in four inbred mouse strains. In vivo insulin secretion was greatest in 129X1/Sv mice, but the counter-regulatory response to hypoglycemia was blunted. FVB/N mice in vivo showed no increase in glucose-stimulated insulin secretion, relative hepatic insulin resistance, and the highest counter-regulatory response to hypoglycemia. In DBA/2 mice, insulin action was lowest among the strains, and islets isolated had the greatest glucose-stimulated insulin secretion in vitro. In C57BL/6 mice, in vivo physiological responses to hyperinsulinemia at euglycemia and hypoglycemia were intermediate relative to other strains. Insulin secretion by C57BL/6 mice was similar to that in other strains in contrast to the blunted glucose-stimulated insulin secretion from isolated islets.CONCLUSIONS-Strain-dependent differences exist in four inbred mouse strains frequently used for genetic manipulation and study of glucose metabolism. These results are important for selecting inbred mice to study glucose metabolism and for interpreting and designing experiments. Diabetes 57:1790-1799, 2008 T he development of new mouse models has allowed investigators to address questions related to glucose metabolism in ways that were not previously possible. Use of inbred mouse strains and proliferation of techniques to produce genetic modifications have been invaluable in defining the role of select genes under physiological conditions. To rigorously examine complex physiological processes in vivo has required the development of new experimental approaches for the mouse and the adaptation of techniques previously used in larger animals. Important technical advancements, including surgical catheterization (1) and miniaturization of clamp techniques (2) for the mouse, have furthered our ability to dissect the physiology underlying insulin action, insulin secretion, and counter-regulation to insulin-induced hypoglycemia under well-controlled physiological conditions.Mouse models produced through genetic modification have been generated in a variety of mouse strains. It is widely recognized that the background mouse strain can influence phenotypes. Several examples have been described where identical genetic mutations in different inbred mouse strains result in different phenotypes (3-5). These findings indicate that the contribution of the inbred strain genetic background to the phenotype is an important factor to consider when designing and interpreting experiments.The goal of the current s...
Stimulation of nitric oxide-cGMP signaling results in vascular relaxation and increased muscle glucose uptake. We show that chronically inhibiting cGMP hydrolysis with the phosphodiesterase-5 inhibitor sildenafil improves energy balance and enhances in vivo insulin action in a mouse model of diet-induced insulin resistance. High-fat-fed mice treated with sildenafil plus L-arginine or sildenafil alone for 12 weeks had reduced weight and fat mass due to increased energy expenditure. However, uncoupling protein-1 levels were not increased in sildenafil-treated mice. Chronic treatment with sildenafil plus L-arginine or sildenafil alone increased arterial cGMP levels but did not adversely affect blood pressure or cardiac morphology. Sildenafil treatment, with or without l-arginine, resulted in lower fasting insulin and glucose levels and enhanced rates of glucose infusion, disappearance, and muscle glucose uptake during a hyperinsulinemic (4 mU x kg(-1) x min(-1))-euglycemic clamp in conscious mice. These effects occurred without an increase in activation of muscle insulin signaling. An acute treatment of high fat-fed mice with sildenafil plus l-arginine did not improve insulin action. These results show that phosphodiesterase-5 is a potential target for therapies aimed at preventing diet-induced energy imbalance and insulin resistance.
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