An acute increase in hypothalamic glucose and its downstream metabolite lactate lower glucose production (GP) and plasma glucose (PG) levels in normal rodents. However, the effectiveness of this nutrient-sensing mechanism in metabolic disease is unknown. We assessed the effects of intracerebroventricular (i.c.v.) or intra-hypothalamic glucose and lactate on in vivo glucose kinetics in conscious rats. Study I revealed that i.c.v. lactate lowered PG via a suppression of GP in rodents with uncontrolled diabetes and diet-induced insulin resistance. Study II demonstrated that i.c.v. glucose was ineffective at suppressing GP in uncontrolled diabetic rodents or rodents with a prior 24 h whole-body or hypothalamic hyperglycemic insult. When PG levels per se were normalized in diabetic rodents hypothalamic glucose sensing to lower GP was rescued. As such, sustained hyperglycemia per se impairs hypothalamic glucose effectiveness in diabetes. Further studies are necessary to determine defective mechanisms upstream of lactate metabolism hindering CNS glucose sensing.

An acute increase in hypothalamic glucose and its downstream metabolite lactate lower glucose production (GP) and plasma glucose (PG) levels in normal rodents. However, the effectiveness of this nutrient-sensing mechanism in metabolic disease is unknown. We assessed the effects of intracerebroventricular (i.c.v.) or intra-hypothalamic glucose and lactate on in vivo glucose kinetics in conscious rats. Study I revealed that i.c.v. lactate lowered PG via a suppression of GP in rodents with uncontrolled diabetes and diet-induced insulin resistance. Study II demonstrated that i.c.v. glucose was ineffective at suppressing GP in uncontrolled diabetic rodents or rodents with a prior 24 h whole-body or hypothalamic hyperglycemic insult. When PG levels per se were normalized in diabetic rodents hypothalamic glucose sensing to lower GP was rescued. As such, sustained hyperglycemia per se impairs hypothalamic glucose effectiveness in diabetes. Further studies are necessary to determine defective mechanisms upstream of lactate metabolism hindering CNS glucose sensing.

Hypothalamic AMP-activated protein kinase (AMPK) regulates energy homeostasis in response to nutritional and hormonal signals. However, its role in glucose production regulation remains to be elucidated. Here, we tested the hypothesis that bidirectional changes in hypothalamic AMPK activity alter glucose production in rodents. First, we found that knocking down hypothalamic AMPK activity in an in vivo rat model led to a significant suppression of glucose production independent of changes in food intake and body weight. Second, we showed that activation of hypothalamic AMPK negated the ability of hypothalamic glucose- and lactate- sensing to lower glucose production. Collectively, these data indicate that changes in hypothalamic AMPK activity are sufficient and necessary for hypothalamic nutrient-sensing mechanisms to alter glucose production in vivo, and highlight the novel role of hypothalamic AMPK in the maintenance of glucose homeostasis in addition to energy balance.

Hypothalamic AMP-activated protein kinase (AMPK) regulates energy homeostasis in response to nutritional and hormonal signals. However, its role in glucose production regulation remains to be elucidated. Here, we tested the hypothesis that bidirectional changes in hypothalamic AMPK activity alter glucose production in rodents. First, we found that knocking down hypothalamic AMPK activity in an in vivo rat model led to a significant suppression of glucose production independent of changes in food intake and body weight. Second, we showed that activation of hypothalamic AMPK negated the ability of hypothalamic glucose- and lactate- sensing to lower glucose production. Collectively, these data indicate that changes in hypothalamic AMPK activity are sufficient and necessary for hypothalamic nutrient-sensing mechanisms to alter glucose production in vivo, and highlight the novel role of hypothalamic AMPK in the maintenance of glucose homeostasis in addition to energy balance.

No description available.

Diabetes mellitus is a major public health concern. Although the accessible novel drugs, techniques, and surgical intervention has improved the survival rate of individuals with diabetes, the prevalence of diabetes is still rising. Type 2 diabetes (T2D) is a result of chronic insulin resistance (IR) and loss of β-cell mass and function. Therefore, the search for naturally occurring, low-cost, and safe compounds that could enhance insulin sensitivity and protect functional β-cell mass can be an effective strategy to prevent this disease. Kaempferol, a flavonol present in various medicinal herbs and edible plants, has been shown to elicit various pharmacological activities in preclinical studies. However, studies investigating the effect of kaempferol on diabetes are limited. In this dissertation, I explored the anti-diabetic potential of dietary intake of kaempferol in diet-induced obese mice and insulin-deficient diabetic mice. First, kaempferol was supplemented in the diet to determine whether it can prevent IR and hyperglycemia in high fat (HF) diet-induced obese mice or STZ-induced obese diabetic mice. To evaluate its efficacy for treating diabetes, kaempferol was administrated once daily via oral gavage to diet-induced obese and insulin-resistant mice or lean STZ-induced diabetic mice. The results demonstrated that long-term oral administration of kaempferol prevents HFD-induced metabolic disorders in middle-aged obese mice. Oral administration of kaempferol improved glucose intolerance and insulin sensitivity, and this effect was associated with increased Glut4 and AMPKa expression in muscle and adipose tissues. Consistent with our findings from the in iii vitro study in C2C12 muscle cell line, these findings suggest that kaempferol may reduce IR at the molecular level by improving glucose metabolism in peripheral tissues. In the second study, dietary kaempferol supplementation prevented hyperglycemia and glucose intolerance by protecting β-cell against the induced damage in obese STZ-induced diabetic mice. In the third study, the administration of kaempferol by oral gavage significantly ameliorated hyperglycemia and glucose intolerance and reduced the incidence of diabetes from 100 % to 77.8% in lean STZinduced diabetic mice. This kaempferol effect was associated with reduced hepatic glucose production, the primary contributor to hyperglycemia, and increased glucose oxidation in the muscle of diabetic mice. Kaempferol treatment restored hexokinase activity in the liver and skeletal muscle and reduced pyruvate carboxylase (PC) activity and glycogenolysis in the liver. Unlike its effect on T2D mice, kaempferol effect in lean STZ-induced diabetic mice was not associated with changes in plasma insulin levels. In the last study, we found that administration of kaempferol by oral gavage significantly improved blood glucose control by suppressing hepatic glucose production and improving glucose intolerance in obese insulin-resistant mice. Similar to its effect in old obese mice, kaempferol enhanced whole-body insulin sensitivity. Kaempferol increased Akt and hexokinase activity and decreased PC activity in the liver. However, kaempferol did not exert any changes in glucose metabolism or insulin sensitivity when administered to healthy lean mice. Overall, findings from these studies provide new insight into the role of kaempferol in the regulation of glucose homeostasis and suggest that kaempferol may be a naturally occurring anti-diabetic compound by improving insulin sensitivity, improving glucose regulation and metabolism, and preserving functional β-cell mass. / Ph. D.

This thesis investigates the ability of rainbow trout to modulate hepatic glucose production (Ra) and disposal (Rd). My goals were to determine: (1) if resting trout can modulate fluxes to cope with exogenous glucose; (2) how fluxes change during graded swimming; (3) how exogenous glucose affects swimming kinetics; and (4) if exogenous glucose affects cost of transport or performance. Results show that resting trout suppress Ra completely and stimulate Rd from 10.6 to 27.6 μmol kg-1 min-1. During swimming, fluxes increase from 15.6 to 21.9 μmol kg-1 min-1, but only at speeds >2.4 BL s-1. When given glucose, trout suppress Ra from 16.4 to 4.1 μmol kg-1 min-1 and stimulate Rd from 16.4 to 40.1 μmol kg-1 min-1. Glucose lowers metabolic rate but does not affect critical swimming speed. Therefore, this research shows that rainbow trout have a much better capacity for glucoregulation than generally suggested by current literature.

Rainbow trout (Oncorhynchus mykiss) is an important freshwater fish whose glucose intolerance, white muscle lactate retention and high lipolytic inertia, have interested comparative physiologists for decades. Recent advancements in mammalian G-protein coupled receptor deorphanization research have identified many endogenous metabolites as regulators of energy metabolism, including lactate and long-chain fatty acids. In addition to being essential metabolic fuels, lactate and long-chain fatty acids regulate lipolysis and lipogenesis by binding to hydroxycarboxylic acid receptor 1 (HCAR1) and the free fatty acid receptors (FFAR1 and 4), respectively. Therefore, the goal of this thesis was to quantify the effects of exogenous lactate and lipids on glucose and fatty acid mobilization in rainbow trout and identify potential signaling mechanisms by monitoring the expression and activity of key glycolytic, gluconeogenic, lipolytic, lipogenic and β-oxidation targets in the liver, muscle and adipose tissue. In Chapter 2, in vivo measurements of metabolic fuel kinetics show that lactate (i) strongly reduced hepatic glucose production by substituting glucose for lactate and (ii) exhibited no lipolytic suppression suggesting HCAR1 signaling is weak in trout. In Chapter 3, in vivo measurements of energy mobilization show that Intralipid strongly induced lipolysis by saturating circulating lipases while transcriptional induction of gluconeogenesis compensates for the acute reduction in hepatic glucose production. Intralipid infusion increased total fatty acid concentration and altered fatty acid composition while suppressing lipid metabolism of trout liver and adipose tissue. In Chapter 4, I identify the presence (hcar1 and ffar1) and absence (ffar4) of these G-protein coupled receptor genes in the rainbow trout genome and describe their evolutionary origins, using in silico approaches of microsynteny, amino acid sequence similarity and critical residue conservation. However, their importance in fish physiology remains relatively unknown, thus future studies are warranted to further investigate such metabolic signals.

Une alimentation HP permet une importante diminution de la prise alimentaire, chez l’Homme et l’animal, par rapport à une alimentation STD. Les précédents travaux du laboratoire montrent que le mécanisme d’action des protéines implique une induction de la PIG chez le rat en période post-absorptive. Ce glucose, libéré et détecté dans la veine porte, permet l’activation de noyaux hypothalamiques impliqués dans la régulation des sensations de satiété. L’objectif de ce travail consistait à mettre en évidence le type de peptides pouvant induire la PIG en régime HP et d’essayer de découvrir leur mécanisme d’action. L’activité de la Glc6Pase et de l’expression des protéines Glc6Pase et PEPCK ont été quantifiées chez des rats nourris en régime STD ou HP et perfusés avec des perfusions d’acides aminés, de peptides µ-opioïdes et des solutions de di- ou tri-peptides. Les résultats montrent que le même mécanisme d’action est utilisé par les protéines et les antagonistes µ-opioïdes pour induire la PIG. Des expériences de dénervation portale et une étude immunohistochimique ont démontré la présence de récepteurs µ-opioïdes dans la veine porte probablement impliqués dans cette induction. Des perfusions de di ou tri-peptides chez le rat ont démontré que la PIG était induite par tous les di ou tri-peptides testés. L’étude phénotypique de la souris KO µ-opioïde nourrie en régime STD, HP ou ayant subi des perfusions portales de di ou tri-peptides, ont confirmé que la PIG pouvait être induite par des di ou tri-peptides et que leur mécanisme d’action nécessitait la présence de récepteurs µ-opioïdes. Cette étude suggère que tous les di- ou tri-peptides produits par la dégradation des protéines pourraient induire la PIG par un mécanisme dépendant des récepteurs µ-opioïdes / Protein feeding promotes an important decrease of food intake in humans and animals, compared on chow diet. Previous data show that this mechanism implicates intestinal glucose production (IPG) induction in rat during the post-absorptive time. Glucose released and detected into the portal vein produces an activation of hypothalamic nuclei implicated in the regulation of satiety sensations. The aim of this study was to highlight peptides which could induce IPG on HP diet and try to discoverer them mechanism. Quantification of Glc6Pase and protein expression of Glc6Pase and PEPCK were assessed in rats fed on chow or HP diet and infused with amino acids, µ-opioïd peptides and di- or tri-peptides. Our results show that the same mechanism is shared by both proteins and µ-opioïd antagonists to induce IGP. Experiments of portal vein denervation and an immunochemistry study showed that µ-opioïd receptors are present in the portal vein, probably implicated in this induction. Di or tri-peptides infusions in rat exhibited that the IGP was induced by all tested di or tri-peptides. Phenotypic study of µ-opioid mice fed on chow, HP diet or having undergone portal vein infusions of di or tri-peptides, confirmed that IGP could be induced by di or tri-peptides and their mechanism takes place with µ-opioïd receptors. This study suggests that all di or tri-peptide produced by protein degradation could induce IGP by a µ-opioïd receptor-dependent mechanism

<p>Obesity is a major health problem in the Western world. Mean birth weight has increased during the last 25 years. One explanation is that the proportion of large for gestational age (LGA) infants has increased. Such infants risk developing obesity, cardiovascular disease and diabetes later in life. Despite the risk of neonatal hypoglycemia, their postnatal metabolic adaptation has not been investigated. Our data, obtained with stable isotope labeled compounds, demonstrate that newborn LGA infants have increased lipolysis and decreased insulin sensitivity. After administration of glucagon, the plasma levels of glucose and the rate of glucose production increased. The simultaneous increase in insulin correlated with the decrease in lipolysis, indicating an antilipolytic effect of insulin in these infants.</p><p>We also demonstrated an intergenerational effect of being born LGA, since women born LGA, were at higher risk of giving birth to LGA infants than women not born LGA. Further, the LGA infants formed three subgroups: born long only, born heavy only, and born both long and heavy. Infants born LGA of women with high birth weight or adult obesity were at higher risk of being LGA concerning weight alone, predisposing to overweight and obesity at childbearing age. In addition we found that pregnant women with gestational diabetes were at increased risk of giving birth to infants that were heavy alone. This could explain the risk of both perinatal complications and later metabolic disease in infants of this group of women.</p><p>To identify determinants of fetal growth, 20 pregnant women with a wide range of fetal weights were investigated at 36 weeks of gestation. Maternal fat mass was strongly associated with insulin resistance. Insulin resistance was related to glucose production, which correlated positively with fetal size. The variation in resting energy expenditure, which was closely related to fetal weight, was largely explained by BMI, insulin resistance, and glucose production. Lipolysis was not rate limiting for fetal growth in this group of women. Consequently, high maternal glucose production due to a high fat mass may result in excessive fetal growth.</p>