Early rise in blood pressure following administration of adrenocorticotropic hormone-[1-24] in humans

1. An elevation in blood pressure has been consistently observed 24 h after adrenocorticotropic hormone (ACTH) administration and is caused by increased ACTH-stimulated cortisol secretion, in association with increased cardiac output. The aim of the present study was to investigate the previously undefined time of onset of this increase in blood pressure in normal humans. 2. Ten normal healthy volunteers received 250 mug ACTH-[1-24], in 500 mL normal saline, infused at a constant rate over 8 h. Six subjects also received a placebo infusion (normal saline only). Blood pressure, heart rate and cortisol levels were determined hourly. Adrenocorticotropic hormone (ACTH-[1-24] plus native ACTH) was measured at 0, 1, 7 and 8 h. 3. Infusion of ACTH-[1-24] produced maximal secretion rates of cortisol, resulting in a mean peak plasma level of 985 +/- 46 nmol/L at 8 h. In response, blood pressure and heart rate rose significantly by 2 h and remained generally elevated for the duration of the infusion. 4. The early onset of haemodynamic responses is consistent with classical steroid receptor-mediated genomic mechanisms, but could be due non-genomic mechanisms. 5. The cardiovascular consequences of therapeutic use of ACTH are well recognized. This results of the present study suggest that even diagnostic administration of ACTH, delivered over a few hours, may raise blood pressure.

Genetic Covariation between Serum {gamma}-Glutamyltransferase Activity and Cardiovascular Risk Factors

Background: Several studies have shown that variation in serum gamma-glutamyltransferase (GGT) in the population is associated with risk of death or development of cardiovascular disease, type 2 diabetes, stroke, or hypertension. This association is only partly explained by associations between GGT and recognized risk factors. Our aim was to estimate the relative importance of genetic and environmental sources of variation in GGT as well as genetic and environmental sources of covariation between GGT and other liver enzymes and markers of cardiovascular risk in adult twin pairs. Methods: We recruited 1134 men and 2241 women through the Australian Twin Registry. Data were collected through mailed questionnaires, telephone interviews, and by analysis of blood samples. Sources of variation in GGT, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) and of covariation between GGT and cardiovascular risk factors were assessed by maximum-likelihood model-fitting. Results: Serum GGT, ALT, and AST were affected by additive genetic and nonshared environmental factors, with heritabilities estimated at 0.52, 0.48, and 0.32, respectively. One-half of the genetic variance in GGT was shared with ALT, AST, or both. There were highly significant correlations between GGT and body mass index; serum lipids, lipoproteins, glucose, and insulin; and blood pressure. These correlations were more attributable to genes that affect both GGT and known cardiovascular risk factors than to environmental factors. Conclusions: Variation in serum enzymes that reflect liver function showed significant genetic effects, and there was evidence that both genetic and environmental factors that affect these enzymes can also affect cardiovascular risk. (C) 2002 American Association for Clinical Chemistry.

Acute stress hyperglycemia in cats is associated with struggling and increased concentrations of lactate and norepinephrine

We characterized the changes in blood glucose concentrations in healthy cats exposed to a short stressor and determined the associations between glucose concentrations, behavioral indicators of stress, and blood variables implicated in stress hyperglycemia (plasma glucose, lactate, insulin, glucagon, cortisol, epinephrine, and norepinephrine concentrations). Twenty healthy adult cats with normal glucose tolerance had a 5-minute spray bath. Struggling and vocalization were the most frequent behavioral responses. There was a strong relationship between struggling and concentrations of glucose and lactate. Glucose and lactate concentrations increased rapidly and significantly in all cats in response to bathing, with peak concentrations occurring at the end of the bath (glucose baseline 83 mg/dL, mean peak 162 mg/dL; lactate baseline 6.3 mg/dL, mean peak 64.0 mg/dL). Glucose response resolved within 90 minutes in 12 of the 20 cats. Changes in mean glucose concentrations were strongly correlated with changes in mean lactate (r =.84; P

Enteral versus parenteral nutrition: comparison of energy metabolism in healthy subjects.

Continuous respiratory exchange measurements were performed on 10 healthy young women for 1 h before, 3 h during, and 3 h after either parenteral (iv) or intragastric (ig) administration of a nutrient mixture (52% glucose, 18% amino acid, and 30% lipid energy) infused at twice the postabsorptive resting energy expenditure (REE). REE rose from 0.98 +/- 0.02 (iv) and 0.99 +/- 0.02 kcal/min (ig) postabsorptively to 1.13 +/- 0.03 (iv) and 1.13 +/- 0.02 kcal/min (ig), resulting in nutrient-induced thermogenesis of 10 +/- 0.6 and 9.3 +/- 0.9%, respectively, when related to the metabolizable energy. The respiratory quotient rose from preinfusion values of 0.81 +/- 0.02 (iv) and 0.80 +/- 0.01 (ig) to 0.86 +/- 0.01 (iv) and 0.85 +/- 0.01 (ig). After nutrient administration the respiratory quotient fell significantly to below the preinfusion values. Plasma glucose and insulin concentrations rose during nutrient administration but were higher during the intravenous route. It is concluded that, although the response time to intragastric administration was delayed, the thermic effects and overall substrate oxidations were comparable during intravenous or intragastric administration, albeit, at lower plasma glucose and insulin concentrations via the intragastric route.

Thermogenic effect of amrinone in healthy men.

OBJECTIVES: The thermogenic effect of amrinone is unknown and its utilization in patients with severe cardiac failure could potentially increase oxygen requirements and therefore aggravate oxygen debt. Consequently, the present study was undertaken to assess the thermogenic response to amrinone at three different plasma concentrations under controlled conditions and to analyze amrinone's effects on various biochemical variables. DESIGN: A prospective, unblinded, controlled study. The initial control period was followed by three sequential, experimental treatments. SUBJECTS: Ten young, healthy, male volunteers with normal body weight. INTERVENTIONS: Three experimental periods. Amrinone was administered intravenously in progressive doses: a) 0.5 mg/kg followed by 5 micrograms/kg/min; b) 0.5 mg/kg followed by 10 micrograms/kg/min; and c) 1.0 mg/kg followed by 10 micrograms/kg/min. MEASUREMENTS AND MAIN RESULTS: Oxygen consumption (VO2) and CO2 production were continuously measured by means of a computerized indirect calorimeter. At the highest dose, amrinone produced a slight and significant (p < .01) increase in VO2 and in resting metabolic rate (+4.5% and +3.7%, respectively), while no change in CO2 production or in respiratory quotient occurred throughout the study. At the medium and high doses, amrinone increased plasma free fatty acid concentrations by 38% and 53%, respectively (p < .05). No variation in plasma glucose, lactate, insulin, norepinephrine, or epinephrine concentrations was observed during the study. CONCLUSIONS: Amrinone administered intravenously at therapeutic doses has minimal thermogenic and metabolic effects in humans without cardiac failure.

Role of the transcriptional factor C/EBPbeta in free fatty acid-elicited beta-cell failure.

Fatty acids can favour the development of Type 2 diabetes by reducing insulin secretion and inducing apoptosis of pancreatic beta-cells. Here, we show that sustained exposure of the beta-cell line MIN6 or of isolated pancreatic islets to the most abundant circulating fatty acid palmitate increases the level of C/EBPbeta, an insulin transcriptional repressor. In contrast, two unsaturated fatty acids, oleate and linoleate were without effect. The induction of C/EBPbeta elicited by palmitate was prevented by inhibiting the ERK1/2 MAP kinase pathway or by reducing mitochondrial fatty acid oxidation with an inhibitor of Carnitine Palmitoyl Transferase-1. Overexpression of C/EBPbeta mimicked the detrimental effects of palmitate and resulted in a drastic reduction in insulin promoter activity, impairment in the capacity to respond to secretory stimuli and an increase in apoptosis. Our data suggest a potential involvement of C/EBPbeta as mediator of the deleterious effects of unsaturated free fatty acids on beta-cell function.

Role and therapeutic potential of microRNAs in diabetes.

The discovery in mammalian cells of hundreds of small RNA molecules, called microRNAs, with the potential to modulate the expression of the majority of the protein-coding genes has revolutionized many areas of biomedical research, including the diabetes field. MicroRNAs function as translational repressors and are emerging as key regulators of most, if not all, physiological processes. Moreover, alterations in the level or function of microRNAs are associated with an increasing number of diseases. Here, we describe the mechanisms governing the biogenesis and activities of microRNAs. We present evidence for the involvement of microRNAs in diabetes mellitus, by outlining the contribution of these small RNA molecules in the control of pancreatic beta-cell functions and by reviewing recent studies reporting changes in microRNA expression in tissues isolated from diabetes animal models. MicroRNAs hold great potential as therapeutic targets. We describe the strategies developed for the delivery of molecules mimicking or blocking the function of these tiny regulators of gene expression in living animals. In addition, because changes in serum microRNA profiles have been shown to occur in association with different human diseases, we also discuss the potential use of microRNAs as blood biomarkers for prevention and management of diabetes.

Étude de la fonction de GLUT8 sur un modèle de souris "knock-out"

Résumé GLUT8 est la première des nouvelles isoformes des GLUT récemment identifiés. Il est fortement exprimé dans les testicules et plus faiblement dans les blastocystes, le cerveau, particulièrement au niveau de l'hippocampe, et le coeur. En conditions basales, il est retenu dans un compartiment intracellulaire. Si on l'exprime en surface cellulaire, par la mutation du motif d'internalisation dileucine, il transporte le glucose avec une bonne affinité. Dans le but d'étudier sa fonction au niveau de l'organisme, nous avons créé un modèle de knock out conditionnel, en entourant le dernier exon du gène de GLUT8 par deux sites loxP. En croisant nos souris avec une souche de souris transgénique exprimant la cre-recombinase dans les cellules de la lignée germinale, nous avons généré un modèle de souris portant la délétion totale de GLUT8 de manière constitutionnelle. Les statistiques effectuées sur les premières naissances indiquent qu'une partie des souris knock out ne survit pas, suggérant un rôle de GLUT8 au niveau du développement embryonnaire. Les souris qui ont survécu ne présentent toutefois pas d'anomalies durant la croissance et sont fertiles. Elles ont des taux de glucose et d'insuline sanguins normaux. Au niveau cérébral, la structure de l'hippocampe n'est pas modifiée par la suppression de GLUT8, cependant, les souris GLUT8-/- présentent une prolifération cellulaire augmentée dans le gyrus denté. Cette augmentation de division cellulaire pourrait être la réponse adaptée à une éventuelle augmentation de la mort cellulaire au niveau de l'hippocampe. Elles ne semblent toutefois pas présenter de défauts cognitifs majeurs dans le bassin de Morris en conditions normales. Toutefois, en conditions de jeûne, elles tendent à une meilleure mémorisation à court terme. Les études morphologiques et histologiques au niveau cardiaque n'ont pas révélé de d'hypertrophie au niveau ventriculaire. La stimulation de la contraction à l'isoprotérénol n'a pas mis en évidence de défaut d'adaptation des coeurs GLUT8-/-. Cependant l'analyse fonctionnelle par électrocardiogramme, en conditions basales, a montré une augmentation de la durée de l'onde P, suggérant un défaut dans la dépolarisation des oreillettes. Nos résultats indiquent que GLUT8 ne joue pas un rôle prédominant dans la survie et la fonction basale des souris. Il pourrait jouer un rôle plus important dans des situations stressantes pour l'organisme, comme l'hypoglycémie ou les conditions d'ischémie qui induiraient son expression à la membrane plasmique et stimuleraient le captage du glucose. Abstract GLUT8 was the first of the recently identified isoform of the GLUT family proteins. It is strongly expressed in the testis. It is also found at a lower level in the blastocyst, in heart and in the brain. Under basal conditions, it is retained in the intracellular compartment, but when the internalization motif dileucine is mutated, GLUT8 translocates to the plasma membrane and transports glucose with a relatively high affinity. To study its function in vivo, we created a conditional knock out mouse model. To do so, we targeted the last exon of the GLUT8 gene with two loxP sites. We then crossed these mice with a transgenic model expressing the cre-recombinase in the gem' line to generate a constitutional total knock out mouse. The statistics made on the first breedings showed that some of the knock out mice do not survive, suggesting a role of GLUT8 in the embryonic development. Conversely mice who survive do not show developmental defects and they are fertile with normal glucose and insulin blood levels. In the brain, the general structure of the hippocampus is not modified by the deletion of GLUT8. However, GLUT8-/- mice show an increase in the cell proliferation in the dentate gyms. This cell proliferation could be due to an increase in the cell death in the hippocampus. When tested in the morris water maze, these mice do not show any cognitive defects in the basal conditions, but they have a tendency to learn better in fasted conditions. The morphological and histological studies made at the heart level did not show any cardiac hypertrophy in the ventricles. The stimulation with isoproterenol did not show any adaptation defects in the GLUT8-/- hearts. However, the functional analysis made in basal conditions with the electrocardiogram showed an increase in the P wave length, suggesting a defect in the atrial depolarization in the knock out mice. Overall, our results show that GLUT8 does not play an important role in the basal general functions in the mice, but might play a more important role during whole organism stress. Hypoglycaemia or ischemia, for example could stimulate the GLUT8 translocation to the plasma membrane to increase specifically glucose uptake. Résumé tout public Les différentes cellules de l'organisme possèdent des propriétés particulières, qui leur permettent de maintenir les fonctions de l'organe auquel elles appartiennent. La membrane plasmique qui les délimite sélectionne les substances qui vont pénétrer à l'intérieur de la cellule et permet ainsi de maintenir un environnement interne constant. Le glucose est une source d'énergie importante pour la cellule et doit pouvoir pénétrer à l'intérieur de la cellule. Il utilise pour cela des protéines de transport qui le feront passer de part et d'autre de la membrane. Les protéines de la famille des GLUT (pour GLUcose Transporter) possèdent cette capacité. GLUT8 est un membre de la famille des GLUT identifié récemment. Il possède la capacité de transporter le glucose quand il se présente à la surface de la cellule. Il est principalement exprimé dans les testicules, dans le coeur et le cerveau et durant le développement embryonnaire. Son rôle n'est toutefois pas encore défini. Ce travail consiste à étudier la fonction de GLUT8 au niveau de l'organisme entier. Nous avons créé un modèle de souris dans lesquelles l'expression de GLUT8 a été supprimée pour mettre en évidence son importance dans le maintien de l'intégrité des fonctions du corps. Les observations effectuées sur les souris qui n'expriment plus GLUT8 nous indiquent que leurs cellules prolifèrent plus vite au niveau de l'hippocampe. L'hippocampe est une structure située dans le cerveau qui est impliquée dans les phénomènes d'apprentissage. Les souris qui ont été testées dans des tâches d'apprentissage n'ont malgré cela pas montré une amélioration de la mémorisation. Dans le coeur, la suppression de GLUT8 semble présenter un défaut quand on mesure l'activité électrique du coeur par électrocardiogramme. Toutefois, ils fonctionnent normalement et ne présentent pas de défauts morphologiques en conditions normales. Les expériences effectuées sur les modèles de souris indiquent que GLUT8 ne jouerait pas un rôle prédominant dans le fonctionnement normal du corps. Il pourrait exercer sa fonction dans des situations plus particulières comme l'hypoglycémie, où il permettrait une meilleure capacité à transporter le glucose dans les cellules.

The required beta cell research for improving treatment of type 2 diabetes.

In healthy individuals, insulin resistance is associated with physiological conditions such as pregnancy or body weight gain and triggers an increase in beta cell number and insulin secretion capacity to preserve normoglycaemia. Failure of this beta cell compensation capacity is a fundamental cause of diabetic hyperglycaemia. Incomplete understanding of the molecular mechanisms controlling the plasticity of adult beta cells mechanisms and how these cells fail during the pathogenesis of diabetes strongly limits the ability to develop new beta cell-specific therapies. Here, current knowledge of the signalling pathways controlling beta cell plasticity is reviewed, and possible directions for future research are discussed.

Molecular mechanism of myosin Va recruitment to dense core secretory granules.

The brain-spliced isoform of Myosin Va (BR-MyoVa) plays an important role in the transport of dense core secretory granules (SGs) to the plasma membrane in hormone and neuropeptide-producing cells. The molecular composition of the protein complex that recruits BR-MyoVa to SGs and regulates its function has not been identified to date. We have identified interaction between SG-associated proteins granuphilin-a/b (Gran-a/b), BR-MyoVa and Rab27a, a member of the Rab family of GTPases. Gran-a/b-BR-MyoVa interaction is direct, involves regions downstream of the Rab27-binding domain, and the C-terminal part of Gran-a determines exon specificity. MyoVa and Gran-a/b are partially colocalised on SGs and disruption of Gran-a/b-BR-MyoVa binding results in a perinuclear accumulation of SGs which augments nutrient-stimulated hormone secretion in pancreatic beta-cells. These results indicate the existence of at least another binding partner of BR-MyoVa that was identified as rabphilin-3A (Rph-3A). BR-MyoVa-Rph-3A interaction is also direct and enhanced when secretion is activated. The BR-MyoVa-Rph-3A and BR-MyoVa-Gran-a/b complexes are linked to a different subset of SGs, and simultaneous inhibition of these complexes nearly completely blocks stimulated hormone release. This study demonstrates that multiple binding partners of BR-MyoVa regulate SG transport, and this molecular mechanism is universally used by neuronal, endocrine and neuroendocrine cells.

Role of islet microRNAs in diabetes: which model for which question?

MicroRNAs are important regulators of gene expression. The vast majority of the cells in our body rely on hundreds of these tiny non-coding RNA molecules to precisely adjust their protein repertoire and faithfully accomplish their tasks. Indeed, alterations in the microRNA profile can lead to cellular dysfunction that favours the appearance of several diseases. A specific set of microRNAs plays a crucial role in pancreatic beta cell differentiation and is essential for the fine-tuning of insulin secretion and for compensatory beta cell mass expansion in response to insulin resistance. Recently, several independent studies reported alterations in microRNA levels in the islets of animal models of diabetes and in islets isolated from diabetic patients. Surprisingly, many of the changes in microRNA expression observed in animal models of diabetes were not detected in the islets of diabetic patients and vice versa. These findings are unlikely to merely reflect species differences because microRNAs are highly conserved in mammals. These puzzling results are most probably explained by fundamental differences in the experimental approaches which selectively highlight the microRNAs directly contributing to diabetes development, the microRNAs predisposing individuals to the disease or the microRNAs displaying expression changes subsequent to the development of diabetes. In this review we will highlight the suitability of the different models for addressing each of these questions and propose future strategies that should allow us to obtain a better understanding of the contribution of microRNAs to the development of diabetes mellitus in humans.

Dietary obesity-associated Hif1α activation in adipocytes restricts fatty acid oxidation and energy expenditure via suppression of the Sirt2-NAD+ system.

Dietary obesity is a major factor in the development of type 2 diabetes and is associated with intra-adipose tissue hypoxia and activation of hypoxia-inducible factor 1α (HIF1α). Here we report that, in mice, Hif1α activation in visceral white adipocytes is critical to maintain dietary obesity and associated pathologies, including glucose intolerance, insulin resistance, and cardiomyopathy. This function of Hif1α is linked to its capacity to suppress β-oxidation, in part, through transcriptional repression of sirtuin 2 (Sirt2) NAD(+)-dependent deacetylase. Reduced Sirt2 function directly translates into diminished deacetylation of PPARγ coactivator 1α (Pgc1α) and expression of β-oxidation and mitochondrial genes. Importantly, visceral adipose tissue from human obese subjects is characterized by high levels of HIF1α and low levels of SIRT2. Thus, by negatively regulating the Sirt2-Pgc1α regulatory axis, Hif1α negates adipocyte-intrinsic pathways of fatty acid catabolism, thereby creating a metabolic state supporting the development of obesity.

Continuous versus single bolus enteral nutrition: comparison of energy metabolism in humans.

Continuous respiratory exchange measurements were performed on five women and five men for 1 h before and 6 h after the administration of a milkshake (53% carbohydrates, 30% lipid, and 17% protein energy) given either as a single bolus dose or continuously during 3 h using a nasogastric tube. The energy administered corresponded to 2.3 times the postabsorptive resting energy expenditure. Resting energy expenditure, respiratory quotient, plasma glucose, and insulin concentrations increased sooner and steeper, and plasma free fatty acids levels decreased earlier with the meal ingested as a single dose than with continuous administration. The magnitude of nutrient-induced thermogenesis was greater (P less than 0.01) with the single dose (means +/- SE, 10.0 +/- 0.6%) than with the continuous administration (8.1 +/- 0.5%). The overall (6 h) substrate balances were not significantly different between the two modes of administration. It is concluded that the mode of enteral nutrient administration influences the immediate thermogenic response as well as changes in respiratory quotient, glycemia, and insulinemia; however, the overall nutrient balance was not affected by the mode of enteral nutrient administration.

Clustering of cardiovascular risk factors mimicking the human metabolic syndrome X in eNOS null mice.

AIMS/HYPOTHESIS: The metabolic syndrome comprises a clustering of cardiovascular risk factors but the underlying mechanism is not known. Mice with targeted disruption of endothelial nitric oxide synthase (eNOS) are hypertensive and insulin resistant. We wondered, whether eNOS deficiency in mice is associated with a phenotype mimicking the human metabolic syndrome. METHODS AND RESULTS: In addition to arterial pressure and insulin sensitivity (euglycaemic hyperinsulinaemic clamp), we measured the plasma concentration of leptin, insulin, cholesterol, triglycerides, free fatty acids, fibrinogen and uric acid in 10 to 12 week old eNOS-/- and wild type mice. We also assessed glucose tolerance under basal conditions and following a metabolic stress with a high fat diet. As expected eNOS-/- mice were hypertensive and insulin resistant, as evidenced by fasting hyperinsulinaemia and a roughly 30 percent lower steady state glucose infusion rate during the clamp. eNOS-/- mice had a 1.5 to 2-fold elevation of the cholesterol, triglyceride and free fatty acid plasma concentration. Even though body weight was comparable, the leptin plasma level was 30% higher in eNOS-/- than in wild type mice. Finally, uric acid and fibrinogen were elevated in the eNOS-/- mice. Whereas under basal conditions, glucose tolerance was comparable in knock out and control mice, on a high fat diet, knock out mice became significantly more glucose intolerant than control mice. CONCLUSIONS: A single gene defect, eNOS deficiency, causes a clustering of cardiovascular risk factors in young mice. We speculate that defective nitric oxide synthesis could trigger many of the abnormalities making up the metabolic syndrome in humans.

Tomosyn-1 is involved in a post-docking event required for pancreatic beta-cell exocytosis.

Although the assembly of a ternary complex between the SNARE proteins syntaxin-1, SNAP25 and VAMP2 is known to be crucial for insulin exocytosis, the mechanisms controlling this key event are poorly understood. We found that pancreatic beta-cells express different isoforms of tomosyn-1, a syntaxin-1-binding protein possessing a SNARE-like motif. Using atomic force microscopy we show that the SNARE-like domain of tomosyn-1 can form a complex with syntaxin-1 and SNAP25 but displays binding forces that are weaker than those observed for VAMP2 (237+/-13 versus 279+/-3 pN). In pancreatic beta-cells tomosyn-1 was found to be concentrated in cellular compartments enriched in insulin-containing secretory granules. Silencing of tomosyn-1 in the rat beta-cell line INS-1E by RNA interference did not affect the number of secretory granules docked at the plasma membrane but led to a reduction in stimulus-induced exocytosis. Replacement of endogenous tomosyn-1 with mouse tomosyn-1, which differs in the nucleotide sequence from its rat homologue and escapes silencing, restored a normal secretory rate. Taken together, our data suggest that tomosyn-1 is involved in a post-docking event that prepares secretory granules for fusion and is necessary to sustain exocytosis of pancreatic beta-cells in response to insulin secretagogues.