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- Author: Sandra Pereira x
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Institute of Medical Sciences, University of Toronto, Toronto, Ontario, Canada
Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada
Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada
Banting & Best Diabetes Centre, Toronto, Ontario, Canada
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Banting & Best Diabetes Centre, Toronto, Ontario, Canada
Department of Physiology, University of Toronto, Toronto, Ontario, Canada
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Department of Physiology, University of Toronto, Toronto, Ontario, Canada
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Metabolic tests are vital to determine in vivo insulin sensitivity and glucose metabolism in preclinical models, usually rodents. Such tests include glucose tolerance tests, insulin tolerance tests, and glucose clamps. Although these tests are not standardized, there are general guidelines for their completion and analysis that are constantly being refined. In this review, we describe metabolic tests in rodents as well as factors to consider when designing and performing these tests.
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Department of Physiology, Department of Medicine, Toronto General Research Institute, Banting and Best Diabetes Centre, Institute of Medical Science, School of Pharmacy, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
Department of Physiology, Department of Medicine, Toronto General Research Institute, Banting and Best Diabetes Centre, Institute of Medical Science, School of Pharmacy, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
Department of Physiology, Department of Medicine, Toronto General Research Institute, Banting and Best Diabetes Centre, Institute of Medical Science, School of Pharmacy, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
Department of Physiology, Department of Medicine, Toronto General Research Institute, Banting and Best Diabetes Centre, Institute of Medical Science, School of Pharmacy, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
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Department of Physiology, Department of Medicine, Toronto General Research Institute, Banting and Best Diabetes Centre, Institute of Medical Science, School of Pharmacy, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
Department of Physiology, Department of Medicine, Toronto General Research Institute, Banting and Best Diabetes Centre, Institute of Medical Science, School of Pharmacy, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
Department of Physiology, Department of Medicine, Toronto General Research Institute, Banting and Best Diabetes Centre, Institute of Medical Science, School of Pharmacy, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
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Circulating free fatty acids (FFAs) are elevated in obesity and cause insulin resistance. The objective of the current study was to determine whether the antioxidant N-acetyl-l-cysteine (NAC) prevented hepatic and peripheral insulin resistance caused by prolonged elevation of plasma FFAs. Chronically cannulated Wistar rats received saline (SAL), Intralipid plus heparin (IH), IH plus NAC, or NAC i.v. infusion for 48 h. Insulin sensitivity was determined using the hyperinsulinemic–euglycemic clamp with tritiated glucose tracer. IH induced hepatic and peripheral insulin resistance (P<0.05). NAC co-infusion did not prevent insulin resistance in the liver, although it was able to prevent peripheral insulin resistance. Prolonged IH infusion did not appear to induce oxidative stress in the liver because hepatic content of protein carbonyl, malondialdehyde, and reduced to oxidized glutathione ratio did not differ across treatment groups. In alignment with our insulin sensitivity results, IH augmented skeletal muscle protein carbonyl content and this was prevented by NAC co-infusion. Taken together, our results indicate that oxidative stress mediates peripheral, but not hepatic, insulin resistance resulting from prolonged plasma FFA elevation. Thus, in states of chronic plasma FFA elevation, such as obesity, antioxidants may protect against peripheral but not hepatic insulin resistance.
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Department of Physiology, University of Toronto, Department of Medicine, Mount Sinai Hospital, Toronto General Research Institute and Banting and Best Diabetes Centre, University Health Network, Muscle Health Research Center and Physical Activity and Chronic Disease Unit, Faculty of Health, School of Kinesiology and Health Science, York University, Department of Internal Medicine, University of Manitoba, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
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Department of Physiology, University of Toronto, Department of Medicine, Mount Sinai Hospital, Toronto General Research Institute and Banting and Best Diabetes Centre, University Health Network, Muscle Health Research Center and Physical Activity and Chronic Disease Unit, Faculty of Health, School of Kinesiology and Health Science, York University, Department of Internal Medicine, University of Manitoba, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
Department of Physiology, University of Toronto, Department of Medicine, Mount Sinai Hospital, Toronto General Research Institute and Banting and Best Diabetes Centre, University Health Network, Muscle Health Research Center and Physical Activity and Chronic Disease Unit, Faculty of Health, School of Kinesiology and Health Science, York University, Department of Internal Medicine, University of Manitoba, Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
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We have shown in rats that sodium salicylate (SS), which inhibits IkBa kinase B (IKKB), prevents hepatic and peripheral insulin resistance caused by short-term (7 h) i.v. administration of Intralipid and heparin (IH). We wished to further determine whether this beneficial effect of SS persisted after prolonged (48 h) IH infusion, which better mimics the chronic free fatty acid (FFA) elevation of obesity. Hence, we performed hyperinsulinemic euglycemic clamps with tritiated glucose methodology to determine hepatic and peripheral insulin sensitivity in rats infused with saline, IH, IH and SS, or SS alone. SS prevented peripheral insulin resistance (P<0.05) caused by prolonged plasma FFA elevation; however, it did not prevent hepatic insulin resistance. In skeletal muscle, protein levels of phospho-IkBa were augmented by prolonged IH administration and this was prevented by SS, suggesting that IH activates while SS prevents the activation of IKKB. Markers of IKKB activation, namely protein levels of phospho-IkBa and IkBa, indicated that IKKB is not activated in the liver after prolonged FFA elevation. Phosphorylation of serine 307 at insulin receptor substrate (IRS)-1, which is a marker of proximal insulin resistance, was not altered by IH administration in the liver, suggesting that this is not a site of hepatic insulin resistance in the prolonged lipid infusion model. Our results suggest that the role of IKKB in fat-induced insulin resistance is time and tissue dependent and that hepatic insulin resistance induced by prolonged lipid elevation is not due to an IRS-1 serine 307 kinase.
Agrarian Sector, Federal University of Paraná, Veterinary Hospital, Curitiba, Brazil
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Department of Anatomy, Federal University of Pernambuco, Recife, Brazil
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Obesogenic diets are known to induce obesity and changes in food intake in experimental animals. Obesity negatively affects the peripheral metabolism and neural aspects, such as changes in eating behavior. In obese animals, dopamine (DA) receptor levels are reduced. DA is one of the main peptides involved in the motivation and pleasure of eating. A combination of naltrexone/bupropion (NB) has shown promise in controlling metabolic alterations, but there are few studies on how they modulate dopaminergic expression. NB, in addition to reducing food intake and body weight, can modify tyrosine hydroxylase (Th) and DA receptor D2 (Drd2 ) levels in the mesolimbic areas of rats submitted to a high-fat diet (HF). The study evaluated the effect of NB on food intake, body weight, and expression levels of Th, Drd1a, and Drd2 , in the nucleus accumbens and striatum of rats fed on HF diet. Wistar rats were grouped according to diet: standard (n = 20) and HF diet (n = 20). The food intake and body weight were analyzed. The gene expression of Th, Drd1a, and Drd2 was evaluated using real-time PCR. NB combination of 1 mg/kg and 20 mg/kg reduced food intake and body weight, increased Drd2 expression in rats on HF diet, and increased Th in rats on both experimental diets. The level of Drd1a was unchanged. We concluded that bodyweight reduction may be associated with decreased food intake in response to the increased Drd2 expression in the mesolimbic areas of rats that received an HF diet.
