Niels Jacob Aachmann-Andersen

Bed rest reduces metabolic protein content and abolishes exercise-induced mRNA responses in human skeletal muscle.

The aim was to test the hypothesis that 7 days of bed rest reduces mitochondrial number and expression and activity of oxidative proteins in human skeletal muscle but that exercise-induced intracellular signaling as well as mRNA and microRNA (miR) responses are maintained after bed rest. Twelve young, healthy male subjects completed 7 days of bed rest with vastus lateralis muscle biopsies taken before and after bed rest. In addition, muscle biopsies were obtained from six of the subjects prior to, immediately after, and 3 h after 45 min of one-legged knee extensor exercise performed before and after bed rest. Maximal oxygen uptake decreased by 4%, and exercise endurance decreased nonsignificantly, by 11%, by bed rest. Bed rest reduced skeletal muscle mitochondrial DNA/nuclear DNA content 15%, hexokinase II and sirtuin 1 protein content ∼45%, 3-hydroxyacyl-CoA dehydrogenase and citrate synthase activity ∼8%, and miR-1 and miR-133a content ∼10%. However, cytochrome c and vascular endothelial growth factor (VEGF) protein content as well as capillarization did not change significantly with bed rest. Acute exercise increased AMP-activated protein kinase phosphorylation, peroxisome proliferator activated receptor-γ coactivator-1α, and VEGF mRNA content in skeletal muscle before bed rest, but the responses were abolished after bed rest. The present findings indicate that only 7 days of physical inactivity reduces skeletal muscle metabolic capacity as well as abolishes exercise-induced adaptive gene responses, likely reflecting an interference with the ability of skeletal muscle to adapt to exercise.

Alterations of systemic and muscle iron metabolism in human subjects treated with low-dose recombinant erythropoietin

The high iron demand associated with enhanced erythropoiesis during high-altitude hypoxia leads to skeletal muscle iron mobilization and decrease in myoglobin protein levels. To investigate the effect of enhanced erythropoiesis on systemic and muscle iron metabolism under nonhypoxic conditions, 8 healthy volunteers were treated with recombinant erythropoietin (rhEpo) for 1 month. As expected, the treatment efficiently increased erythropoiesis and stimulated bone marrow iron use. It was also associated with a prompt and considerable decrease in urinary hepcidin and a slight transient increase in GDF-15. The increased iron use and reduced hepcidin levels suggested increased iron mobilization, but the treatment was associated with increased muscle iron and L ferritin levels. The muscle expression of transferrin receptor and ferroportin was up-regulated by rhEpo administration, whereas no appreciable change in myoglobin levels was observed, which suggests unaltered muscle oxygen homeostasis. In conclusion, under rhEpo stimulation, the changes in the expression of muscle iron proteins indicate the occurrence of skeletal muscle iron accumulation despite the remarkable hepcidin suppression that may be mediated by several factors, such as rhEpo or decreased transferrin saturation or both.

Sex Hormone-Binding Globulin Levels Predict Insulin Sensitivity, Disposition Index and Cardiovascular Risk During Puberty

OBJECTIVE Early puberty is associated with increased risk of subsequent cardiovascular disease. Low sex hormone–binding globulin (SHBG) levels are a feature of early puberty and of conditions associated with increased cardiovascular risk. The aim of the present study was to evaluate SHBG as a predictor of glucose metabolism and metabolic risk during puberty. RESEARCH DESIGN AND METHODS This was a cross-sectional study on 132 healthy Caucasian children and adolescents evaluated by an oral glucose tolerance test, a dual-energy X-ray absorptiometry scan, direct oxygen uptake measurement during cycle ergometry, and fasting blood samples. RESULTS SHBG levels declined with advancement of puberty in both boys (P < 0.001) and girls (P = 0.019). SHBG was significantly positively associated with insulin sensitivity in boys (P < 0.001) and girls (P < 0.001). In addition, SHBG was a strong predictor of insulin sensitivity (P = 0.001) and the only predictor of the disposition index (P = 0.031) after adjustment for puberty, fat mass, and aerobic fitness. SHBG was significantly negatively associated with metabolic risk (P = 0.032) and with hypersensitive C-reactive protein levels (P = 0.030) after adjustment for relevant confounders. CONCLUSIONS SHBG was a strong predictor of insulin sensitivity and metabolic risk during puberty. Thus, we hypothesize that SHBG integrates the marked changes in glucose metabolism and body composition that occur during the pubertal transition.

Impact of the Growth Hormone Receptor Exon 3 Deletion Gene Polymorphism on Glucose Metabolism, Lipids, and Insulin-Like Growth Factor-I Levels during Puberty

CONTEXT The GH/IGF-I axis has major impact on insulin sensitivity and insulin secretion. Recently a polymorphism in the GH receptor gene (GHR), a genomic deletion of exon 3 (GHRd3), has been linked to increased responsiveness to GH. OBJECTIVE The objective of the present study was to evaluate the impact of the GHRd3 gene polymorphism on insulin sensitivity, insulin secretion, lipids, and IGF-I levels in healthy children and adolescents. DESIGN This was cross-sectional and was part of the COPENHAGEN puberty study. SETTING The study was conducted at a tertiary center for pediatric endocrinology. PARTICIPANTS Participants included 142 healthy Caucasian subjects (65 boys) aged 8.5-16.1 yr. INTERVENTIONS Standard 2-h oral glucose tolerance tests were preformed. GHR genotypes were determined by multiplex PCR. Main outcome measures were insulin sensitivity, insulin secretion, serum lipids, and IGF-I levels. RESULTS Insulin secretion was higher in children and adolescents with a least one GHRd3 allele, even after adjustment for age, sex, pubertal stage, and insulin sensitivity (P = 0.018). Disposition index was higher in GHRd3-positive subjects (P = 0.026). In addition, the GHRd3 allele was associated with higher triglyceride (P = 0.028), but not IGF-I levels. CONCLUSION The presence of at least one GHRd3 allele was associated with higher insulin secretion for a given degree of insulin sensitivity in healthy children and adolescents during puberty. In addition, the presence of the GHRd3 allele was associated with a higher disposition index. Thus, this common polymorphism in the GHR gene might play a role for pancreatic beta-cell compensatory capacity.

Acute hypoxia increases the cerebral metabolic rate – a magnetic resonance imaging study:

The aim of the present study was to examine changes in cerebral metabolism by magnetic resonance imaging of healthy subjects during inhalation of 10% O2 hypoxic air. Hypoxic exposure elevates cerebral perfusion, but its effect on energy metabolism has been less investigated. Magnetic resonance imaging techniques were used to measure global cerebral blood flow and the venous oxygen saturation in the sagittal sinus. Global cerebral metabolic rate of oxygen was quantified from cerebral blood flow and arteriovenous oxygen saturation difference. Concentrations of lactate, glutamate, N-acetylaspartate, creatine and phosphocreatine were measured in the visual cortex by magnetic resonance spectroscopy. Twenty-three young healthy males were scanned for 60 min during normoxia, followed by 40 min of breathing hypoxic air. Inhalation of hypoxic air resulted in an increase in cerebral blood flow of 15.5% (p = 0.058), and an increase in cerebral metabolic rate of oxygen of 8.5% (p = 0.035). Cerebral lactate concentration increased by 180.3% ( p < 10 - 6 ), glutamate increased by 4.7% ( p < 10 - 4 ) and creatine and phosphocreatine decreased by 15.2% (p < 10 - 3 ). The N-acetylaspartate concentration was unchanged (p = 0.36). In conclusion, acute hypoxia in healthy subjects increased perfusion and metabolic rate, which could represent an increase in neuronal activity. We conclude that marked changes in brain homeostasis occur in the healthy human brain during exposure to acute hypoxia.

Comparison of global cerebral blood flow measured by phase-contrast mapping MRI with 15O-H2O positron emission tomography

To compare mean global cerebral blood flow (CBF) measured by phase‐contrast mapping magnetic resonance imaging (PCM MRI) and by 15O‐H2O positron emission tomography (PET) in healthy subjects. PCM MRI is increasingly being used to measure mean global CBF, but has not been validated in vivo against an accepted reference technique.

Hypoxia increases exercise heart rate despite combined inhibition of β-adrenergic and muscarinic receptors

Hypoxia increases the heart rate response to exercise, but the mechanism(s) remains unclear. We tested the hypothesis that the tachycardic effect of hypoxia persists during separate, but not combined, inhibition of β-adrenergic and muscarinic receptors. Nine subjects performed incremental exercise to exhaustion in normoxia and hypoxia (fraction of inspired O2 = 12%) after intravenous administration of 1) no drugs (Cont), 2) propranolol (Prop), 3) glycopyrrolate (Glyc), or 4) Prop + Glyc. HR increased with exercise in all drug conditions (P < 0.001) but was always higher at a given workload in hypoxia than normoxia (P < 0.001). Averaged over all workloads, the difference between hypoxia and normoxia was 19.8 ± 13.8 beats/min during Cont and similar (17.2 ± 7.7 beats/min, P = 0.95) during Prop but smaller (P < 0.001) during Glyc and Prop + Glyc (9.8 ± 9.6 and 8.1 ± 7.6 beats/min, respectively). Cardiac output was enhanced by hypoxia (P < 0.002) to an extent that was similar between Cont, Glyc, and Prop + Glyc (2.3 ± 1.9, 1.7 ± 1.8, and 2.3 ± 1.2 l/min, respectively, P > 0.4) but larger during Prop (3.4 ± 1.6 l/min, P = 0.004). Our results demonstrate that the tachycardic effect of hypoxia during exercise partially relies on vagal withdrawal. Conversely, sympathoexcitation either does not contribute or increases heart rate through mechanisms other than β-adrenergic transmission. A potential candidate is α-adrenergic transmission, which could also explain why a tachycardic effect of hypoxia persists during combined β-adrenergic and muscarinic receptor inhibition.

Transient impairment of the axolemma following regional anaesthesia by lidocaine in humans

We tested the recovery of motor axon conduction and multiple measures of excitability by ‘threshold‐tracking’ after ultrasound‐guided distal median nerve regional anaesthesia by lidocaine. Lidocaine caused a transient conduction failure that recovered completely by 3 h, whereas excitability recovered only partially by 6 h and fully by 24 h. The up to 7‐fold increase in threshold after complete recovery of conduction was associated with excitability changes that could only partially be explained by block of the voltage‐gated Na+ channel (VGSC). Mathematical modelling indicated that, apart from a reduction in the number of functioning VGSCs, lidocaine also caused a decrease of passive membrane resistance and an increase of capacitance. Our data suggest that lidocaine, even at clinical ‘sub‐blocking’ concentrations, could cause a reversible structural impairment of the axolemma.

Adverse metabolic risk profiles in greenlandic inuit children compared to danish children

During recent decades, the prevalence of metabolic morbidity has increased rapidly in adult Greenlandic Inuit. To what extent this is also reflected in the juvenile Inuit population is unknown. The objective was, therefore, in the comparison with Danish children, to evaluate metabolic profiles in Greenlandic Inuit children from the capital in the southern and from the northern most villages

Detection of erythropoietin misuse by the Athlete Biological Passport combined with reticulocyte percentage

The sensitivity of the adaptive model of the Athlete Biological Passport (ABP) and reticulocyte percentage (ret%) in detection of recombinant human erythropoietin (rHuEPO) misuse was evaluated using both a long-term normal dose and a brief high dose treatment regime. Sixteen subjects received either 65 IU rHuEPO × kg-1 every second day for two weeks (normal-dose), 390 IU rHuEPO × kg-1 on three consecutive days (high-dose), or frequent placebo treatment for 13 days in a randomized, placebo-controlled, double-blind crossover design. Blood variables were measured 4, 11, and 25 days following treatment initiation. The ABP based on haemoglobin concentration ([Hb]) and OFF-hr score ([Hb] - 60 × √ret%) yielded atypical profiles following both normal-dose and high-dose treatment (0 %, 31 %, 13 % vs. 21 %, 33 %, 20 % at days 4, 11, and 25 after normal and high dose, respectively). Including ret% as a stand-alone marker for atypical blood profiles increased (P < 0.05) the sensitivity of the adaptive model at day 11 to 63 % and 67 % for normal-dose and high-dose rHuEPO administration, respectively. In conclusion, ~30 % of subjects injecting a normal-dose rHuEPO for two weeks or a high-dose rHuEPO for three days will present an atypical ABP profile. Including ret% as a stand-alone parameter improves the sensitivity two-fold. Copyright