Muscle carnitine availability plays a central role in regulating fuel metabolism in the rodent.

Key Points: Meldonium inhibits endogenous carnitine synthesis and tissue uptake, and accelerates urinary carnitine excretion, although the impact of meldonium-mediated muscle carnitine depletion on whole-body fuel selection, and muscle fuel metabolism and its molecular regulation is under-investigated. Ten days of oral meldonium administration did not impact on food or fluid intake, physical activity levels or body weight gain in the rat, whereas it depleted muscle carnitine content (all moieties), increased whole-body carbohydrate oxidation and muscle and liver glycogen utilization, and reduced whole-body fat oxidation. Meldonium reduced carnitine transporter protein expression across muscles of different contractile and metabolic phenotypes.

Development of microdialysis methodology for interstitial insulin measurement in rodents.

Introduction: Accurate assessment of muscle insulin sensitivity requires measurement of insulin concentration in interstitial fluid (ISF), but has proved difficult. We aimed to optimise measurement of ISF insulin concentrations in rat muscles in vivo using microdialysis.

Methods: Factorial experimental design experiments were performed in vitro to determine optimal conditions for insulin recovery with microdialysis probes.

Age and microenvironment outweigh genetic influence on the Zucker rat microbiome.

Animal models are invaluable tools which allow us to investigate the microbiome-host dialogue. However, experimental design introduces biases in the data that we collect, also potentially leading to biased conclusions. With obesity at pandemic levels animal models of this disease have been developed; we investigated the role of experimental design on one such rodent model.

Differentiating sodium-glucose co-transporter-2 inhibitors in development for the treatment of type 2 diabetes mellitus.

Introduction: Sodium-glucose co-transporter-2 (SGLT2) inhibitors are a novel class of agents for the treatment of type 2 diabetes mellitus (T2DM). By inhibiting SGLT2, they prevent renal glucose reabsorption, resulting in glucosuria.

Areas Covered: The rationale for development of SGLT2 inhibitors is reviewed, with particular focus on the nine SGLT2 inhibitors currently in development.

Targeting the kidney and glucose excretion with dapagliflozin: preclinical and clinical evidence for SGLT2 inhibition as a new option for treatment of type 2 diabetes mellitus.

Sodium-glucose cotransporter-2 (SGLT2) inhibitors are a novel class of glucuretic, antihyperglycemic drugs that target the process of renal glucose reabsorption and induce glucuresis independently of insulin secretion or action. In patients with type 2 diabetes mellitus, SGLT2 inhibitors have been found to consistently reduce measures of hyperglycemia, including hemoglobin A1c, fasting plasma glucose, and postprandial glucose, throughout the continuum of disease. By inducing the renal excretion of glucose and its associated calories, SGLT2 inhibitors reduce weight and have the potential to be disease modifying by addressing the caloric excess that is believed to be one of the root causes of type 2 diabetes mellitus.

Targeting renal glucose reabsorption for the treatment of type 2 diabetes mellitus using the SGLT2 inhibitor dapagliflozin.

Sodium-glucose co-transporter 2 (SGLT2) plays a key role in glucose homeostasis as the key transporter responsible for most renal glucose reabsorption in the proximal tubules of the kidney. Dapagliflozin is a potent, selective, and reversible inhibitor of SGLT2 that lowers blood glucose levels in an insulin-independent fashion. This novel agent has been studied extensively in patients with type 2 diabetes mellitus (T2DM).

Diabetic nephropathy and long-term treatment effects of rosiglitazone and enalapril in obese ZSF1 rats.

Diabetic nephropathy (DN) is a major cause of end-stage renal disease. Yet the pathogenic mechanisms underlying the development of DN are not fully defined, partially due to lack of suitable models that mimic the complex pathogenesis of renal disease in diabetic patients. In this study, we describe early and late renal manifestations of DN and renal responses to long-term treatments with rosiglitazone or high-dose enalapril in ZSF1 rats, a model of metabolic syndrome, diabetes, and chronic renal disease.

Manganese enhancement in non-CNS organs.

Manganese-enhanced magnetic resonance imaging (MEMRI) is a novel imaging technique capable of monitoring calcium influx, in vivo. Manganese (Mn2+) ions, similar to calcium ions (Ca2+), are taken up by activated cells where their paramagnetic properties afford signal enhancement in T(1)-weighted MRI methodologies. In this study we have assessed Mn2+ distribution in mice using magnetization-prepared rapid gradient echo (MP-RAGE) based MRI, by measuring changes in T(1)-effective relaxation times (T(1)-eff), effective R(1)-relaxation rates (R(1)-eff) and signal intensity (SI) profiles over time.

Reversibility of hyperglycaemia and islet abnormalities in the high fat-fed female ZDF rat model of type 2 diabetes.

Introduction: We characterised the development of Type 2 diabetes and associated changes in islet appearance in female ZDF rats and explored its suitability for studies with novel therapeutic agents.

Methods: Female ZDF rats were either chow or high fat (60%) fed for up to 36 days and blood glucose and plasma insulin concentration measured. Additionally, we restored two groups of rats back to chow diet after ten and nineteen days of high fat feeding to determine the reversibility.

Prolonged inhibition of glycogen phosphorylase in livers of Zucker Diabetic Fatty rats models human glycogen storage diseases.

The preclinical efficacy and safety of GPi921, a glycogen phosphorylase inhibitor, was assessed following twenty-eight days of administration to Zucker Diabetic Fatty (ZDF) rats. The ZDF rat is an animal model of type 2 diabetes mellitus (TTDM) which develops severe hyperglycemia. Inhibition of glycogen phosphorylase throughout the duration of the study was demonstrated by reductions in twenty-four-hour glucose profiles and glycated hemoglobin levels.

The intravenous glucose tolerance test in cannulated Wistar rats: a robust method for the in vivo assessment of glucose-stimulated insulin secretion.

Introduction: Glucose-stimulated insulin secretion (GSIS) is critical in mammalian fuel homeostasis and is diminished early in the evolution of beta-cell dysfunction, ultimately contributing to the development of Type 2 diabetes. We sought to standardise and validate the intravenous glucose tolerance test (IVGTT), a commonly used technique to assess GSIS, in anaesthetised and conscious cannulated male Han Wistar rats.

Methods: Male Han Wistar rats were cannulated via the right jugular vein and left carotid artery.

Single dose glucagon (0.5 mg IV bolus) administration in healthy human volunteers is a robust model for assessment of glycogenolysis: characterisation of the glucose excursion after glucagon challenge.

Introduction: In the assessment of potential new treatments for Type 2 diabetes, robust pharmacological methods are helpful in assessing efficacy, defining dose response, duration of effect and ultimately in deciding whether to progress compounds to the next phase of drug development. Hepatic glucose handling is abnormal in Type 2 diabetes. We evaluated glucagon challenge as a way of assessing effects on the glycogenolytic pathway.

Glucagon challenge in the rat: a robust method for the in vivo assessment of Glycogen phosphorlyase inhibitor efficacy.

Introduction: Glycogen phosphorlyase inhibitors (GPi) act on the glycogenolytic pathway decreasing hepatic glucose output, making them potential candidates for Type 2 diabetes treatment. We established a robust in vivo method to assess GPis efficacy utilising glucagon-stimulated glycogenolysis.

Methods: Blood glucose was monitored in both male AP Wistar and AP Zucker rats using tail prick samples pre- and post intraperitoneal or subcutaneous glucagon administration.

Increased sensitivity of glycogen synthesis to phosphorylase-a and impaired expression of the glycogen-targeting protein R6 in hepatocytes from insulin-resistant Zucker fa/fa rats.

Hepatic insulin resistance in the leptin-receptor defective Zucker fa/fa rat is associated with impaired glycogen synthesis and increased activity of phosphorylase-a. We investigated the coupling between phosphorylase-a and glycogen synthesis in hepatocytes from fa/fa rats by modulating the concentration of phosphorylase-a. Treatment of hepatocytes from fa/fa rats and Fa/? controls with a selective phosphorylase inhibitor caused depletion of phosphorylase-a, activation of glycogen synthase and stimulation of glycogen synthesis.

Acetyl group availability influences phosphocreatine degradation even during intense muscle contraction.

We previously established that activation of the pyruvate dehydrogenase complex (PDC) using dichloroacetate (DCA) reduced the reliance on substrate-level phosphorylation (SLP) at the onset of exercise, with normal and reduced blood flow. PDC activation also reduced fatigue development during contraction with reduced blood flow. Since these observations, several studies have re-evaluated our observations.

Acetyl-CoA provision and the acetyl group deficit at the onset of contraction in ischemic canine skeletal muscle.

We examined the effects of increasing acetylcarnitine and acetyl-CoA availability at rest, independent of pyruvate dehydrogenase complex (PDC) activation, on energy production and tension development during the rest-to-work transition in canine skeletal muscle. We aimed to elucidate whether the lag in PDC-derived acetyl-CoA delivery toward the TCA cycle at the onset of exercise can be overcome by increasing acetyl group availability independently of PDC activation or is intimately dependent on PDC-derived acetyl-CoA. Gracilis muscle pretreated with saline or sodium acetate (360 mg/kg body mass) (both n = 6) was sampled repeatedly during 5 min of ischemic contraction.

The glycogenic action of protein targeting to glycogen in hepatocytes involves multiple mechanisms including phosphorylase inactivation and glycogen synthase translocation.

Expression of the glycogen-targeting protein PTG promotes glycogen synthase activation and glycogen storage in various cell types. In this study, we tested the contribution of phosphorylase inactivation to the glycogenic action of PTG in hepatocytes by using a selective inhibitor of phosphorylase (CP-91149) that causes dephosphorylation of phosphorylase a and sequential activation of glycogen synthase. Similar to CP-91194, graded expression of PTG caused a concentration-dependent inactivation of phosphorylase and activation of glycogen synthase.

Fibroblast growth factor 2: from laboratory evidence to clinical application.

Fibroblast growth factor 2 (FGF2) is expressed ubiquitously in mesodermal and neuroectodermal cells. Human FGF2 occurs in isoforms translated from a common mRNA by alternative use of AUG (low-molecular weight isoforms) and CUG (high-molecular weight isoforms) start codons. Whereas the high-molecular weight isoforms function in an intracrine manner, the low-molecular weight isoform functions as autocrine, paracrine, and intracrine ligands.

The temporal relationship between glycogen phosphorylase and activation of the pyruvate dehydrogenase complex during adrenaline infusion in resting canine skeletal muscle.

The present study examined the effect of adrenaline infusion on the activation status of glycogen phosphorylase and the pyruvate dehydrogenase complex (PDC) and on the accumulation of glucose-6-phosphate (G-6-P) and acetylcarnitine in resting canine skeletal muscle. The study was performed in an effort to gain some insight into the temporal relationship between glycogen phosphorylase and PDC activation in vivo in skeletal muscle, which is currently unresolved. Multiple muscle samples were obtained from canine brachial muscle (n = 10) before and during (1, 3, 7 and 15 min) adrenaline infusion (0.

Bicarbonate-induced alkalosis augments cellular acetyl group availability and isometric force during the rest-to-work transition in canine skeletal muscle.

Increasing blood bicarbonate content has long been cited as a potential mechanism to improve contractile function. We investigated whether sodium bicarbonate-induced metabolic alkalosis could positively affect force development during the rest-to-work transition in ischaemic skeletal muscle. Secondly, assuming it could, we investigated whether bicarbonate could augment acetyl group availability through the same equilibrium reaction as sodium acetate pre-treatment and whether this underpins, at least in part, its ergogenic effect.

The acetyl group deficit at the onset of contraction in ischaemic canine skeletal muscle.

Considerable debate surrounds the identity of the precise cellular site(s) of inertia that limit the contribution of mitochondrial ATP resynthesis towards a step increase in workload at the onset of muscular contraction. By detailing the relationship between canine gracilis muscle energy metabolism and contractile function during constant-flow ischaemia, in the absence (control) and presence of pyruvate dehydrogenase complex activation by dichloroacetate, the present study examined whether there is a period at the onset of contraction when acetyl-coenzyme A (acetyl-CoA) availability limits mitochondrial ATP resynthesis, i.e.