Metabolic Rate Research Articles

Glucocorticoid excess alters metabolic rate and substrate utilization via 11β-HSD1

Systemic glucocorticoid excess causes several adverse metabolic conditions, most notably Cushing’s syndrome. These effects are amplified by the intracellular enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Here we determined the less well characterised effects of glucocorticoid excess, and the contribution of 11β-HSD1 amplification, on metabolic rate in mice. Male and female C57BL/6J (wild type, WT) and 11β-HSD1 knock out (11β-HSD1KO) mice were treated with high-dose corticosterone or a vehicle control for 3 weeks. Indirect calorimetry was conducted during the final week of treatment, with or without fasting, to determine the impact on metabolic rate. We found that corticosterone treatment elevated metabolic rate and promoted carbohydrate utilisation primarily in female WT mice, with effects more pronounced during the light phase. Corticosterone treatment also resulted in greater fat accumulation in female WT mice. Corticosterone induced hyperphagia was identified as a likely causal factor altering the respiratory exchange ratio (RER) but not energy expenditure (EE). Male and female 11β-HSD1KO mice were protected against these effects. We identify novel metabolic consequences of sustained glucocorticoid excess, identify a key mechanism of hyperphagia and demonstrate that 11β-HSD1 is required to manifest the full metabolic derangement.

Effects of calorie-restricted diet on health state and intestinal flora in Hashimoto's thyroiditis patients: Study protocol for a randomized controlled trial.

Hashimoto's thyroiditis (HT) is an autoimmune disease, characterized by abnormal elevation in thyroid peroxidase antibody and/or thyroglobulin antibody. In recent decades, HT disease has become more and more widespread. Patients always report multiple symptoms, even though their thyroid hormone levels are kept in normal ranges. However, no treatment exists to effectively reduce the levels of thyroid antibodies. Our study aims to determine whether calorie-restricted diet is helpful in improving health of HT patients. This is a 3-month randomized controlled trial. HT patients will be randomized into a calorie-restricted (CR) group or a calorie-unrestricted control group. All the participants will be instructed to consume a diet that includes a combination of 45-55% calories from carbohydrates, 20-30% from fats, and 15-25% from proteins, according to current Chinese Dietary Guidelines. Participants in CR group need to limit their calories intake equal to their basal energy expenditure, which means that their daily caloric intake will be limited by about 20-30%. The study population is planned to be 66 HT patients aged 18 to 65 years. The primary outcome is change of thyroid antibody levels from baseline. Secondary outcomes include the changes of non-hypothyroid symptoms scores, thyroid function indexes, morphology of thyroid, T lymphocyte subpopulations, inflammatory biomarkers and lipids from baseline to 12 weeks. This trial will have implications for nutrition treatment policy in regard to thyroid antibodies control, immune dysfunction and related non-hypothyroid symptoms improvement among HT patients.

P24-04 Quantifying rate and global profile of gut microbiota metabolism ex vivo by LC-MS/MS

P24-04 Quantifying rate and global profile of gut microbiota metabolism ex vivo by LC-MS/MS

PKM2 regulates metabolic flux and oxidative stress in the murine heart.

Cardiac metabolism ensures a continuous ATP supply, primarily using fatty acids in a healthy state and favoring glucose in pathological conditions. Pyruvate kinase muscle (PKM) controls the final step of glycolysis, with PKM1 being the main isoform in the heart. PKM2, elevated in various heart diseases, has been suggested to play a protective role in cardiac stress, but its function in basal cardiac metabolism remains unclear. We examined hearts from global PKM2 knockout (PKM2-/-) mice and found reduced intracellular glucose. Isotopic tracing of U-13C glucose revealed a shift to biosynthetic pathways in PKM2-/- cardiomyocytes. Total ATP content was two-thirds lower in PKM2-/- hearts, and functional analysis indicated reduced mitochondrial oxygen consumption. Total reactive oxygen species (ROS) and mitochondrial superoxide were also increased in PKM2-/- cardiomyocytes. Intriguingly, PKM2-/- hearts had preserved ejection fraction compared to controls. Mechanistically, increased calcium/calmodulin-dependent kinase II activity and phospholamban phosphorylation may contribute to higher sarcoendoplasmic reticulum calcium ATPase 2 pump activity in PKM2-/- hearts. Loss of PKM2 led to altered glucose metabolism, diminished mitochondrial function, and increased ROS in cardiomyocytes. These data suggest that cardiac PKM2 acts as an important rheostat to maintain ATP levels while limiting oxidative stress. Although loss of PKM2 did not impair baseline contractility, its absence may make hearts more sensitive to environmental stress or injury.

In silico modeling the potential clinical effect of growth factor treatment on the metabolism of human nucleus pulposus cells.

While growth factors have the potential to halt degeneration and decrease inflammation in animal models, the literature investigating the effect of dosage on human cells is lacking. Moreover, despite the completion of clinical trials using growth differentiation factor-5 (GDF-5), no results have been publicly released. The overall objective was to quantitatively assess the effect of three clinically relevant concentrations of GDF-5 (0.25, 1, and 2 mg) as a therapeutic for disc regeneration. Firstly, this work experimentally determined the effects of GDF-5 concentration on the metabolic and matrix synthesis rates of human nucleus pulposus (NP) cells. Secondly, in silico modeling was employed to predict the subsequent regenerative effect of different GDF-5 treatments (± cells). This study suggests a trend of increased matrix synthesis with 0.25 and 1 mg of GDF-5. However, 2 mg of GDF-5 significantly upregulates oxygen consumption. Despite this, in silico models highlight the potential of growth factors in promoting matrix synthesis compared to cell-only treatments, without significantly perturbing the nutrient microenvironment. This work elucidates the potential of GDF-5 on human NP cells. Although the results did not reveal statistical differences across all doses, the variability and response among donors is an interesting finding. It highlights the complexity of human response to biological treatments and reinforces the need for further human research and personalized approaches. Furthermore, this study raises a crucial question about whether these potential biologics are more regenerative in nature or better suited as prophylactic therapies for younger patient groups. Biological agents exhibit unique characteristics and features, demanding tailored development strategies and individualized assessments rather than a one-size-fits-all approach. Therefore, the journey to realizing the full potential of biological therapies is long and costly. Nonetheless, it holds the promise of revolutionizing spinal healthcare and improving the quality of life for patients suffering from discogenic back pain.

Effects of Mesozooplankton Growth and Reproduction on Plankton and Organic Carbon Dynamics in a Marine Biogeochemical Model

AbstractMarine mesozooplankton play an important role for marine ecosystem functioning and global biogeochemical cycles. Their size structure, varying spatially and temporally, heavily impacts biogeochemical processes and ecosystem services. Mesozooplankton exhibit size changes throughout their life cycle, affecting metabolic rates and functional traits. Despite this variability, many models oversimplify mesozooplankton as a single, unchanging size class, potentially biasing carbon flux estimates. Here, we include mesozooplankton ontogenetic growth and reproduction into a 3‐dimensional global ocean biogeochemical model, PISCES‐MOG, and investigate the subsequent effects on simulated mesozooplankton phenology, plankton distribution, and organic carbon export. Utilizing an ensemble of statistical predictive models calibrated with a global set of observations, we generated monthly climatologies of mesozooplankton biomass to evaluate the simulations of PISCES‐MOG. Our analyses reveal that the model and observation‐based biomass distributions are consistent ( = 0.40, total epipelagic biomass: 137 TgC from observations vs. 232 TgC in the model), with similar seasonality (later bloom as latitude increases poleward). Including ontogenetic growth in the model induced cohort dynamics and variable seasonal dynamics across mesozooplankton size classes and altered the relative contribution of carbon cycling pathways. Younger and smaller mesozooplankton transitioned to microzooplankton in PISCES‐MOG, resulting in a change in particle size distribution, characterized by a decrease in large particulate organic carbon (POC) and an increase in small POC generation. Consequently, carbon export from the surface was reduced by 10%. This study underscores the importance of accounting for ontogenetic growth and reproduction in models, highlighting the interconnectedness between mesozooplankton size, phenology, and their effects on marine carbon cycling.

When less is more for dietary Lactobacillus rhamnosus IMC 501: The complex role gut microbiota play in energy budgets and allostasis of early juvenile Mozambique Tilapia (Oreochromis mossambicus)

In aquaculture, exposure to stressors results in heightened neuroendocrine responses, increasing metabolic activities and reducing growth to offset additional stressor-related energetic costs for allostasis. Supplementation with probiotics increases metabolic expenditures from elevated fish digestion and upregulated immune systems, but effects of the probiotics concentrations on energy budgets remains unknown. This study used respirometry to determine the effects of five different probiotic concentrations: T0 control (0 × 1011 CFU/g), T1 (5 × 1011 CFU/g), T2 (10 × 1011 CFU/g), T3 (15 × 1011 CFU/g), and T4 (20 × 1011 CFU/g) of a dietary single-strain probiotic (Lactobacillus rhamnosus IMC 501) on feed consumption, and the proportion of feed intake energy (C) allocated to growth (G), and routine metabolic rates (Rr), in the energy budgets of early juvenile (1-3 g wet weight) Mozambique tilapia (Oreochromis mossambicus), weekly over a 28-day experimental period. Two-factor ANOVA analyses revealed that the amount of feed intake energy (C) increased in probiotic treatments over controls. Allocation of feed energy for growth (G) differed among treatments, but not with time, but for routine metabolic activities (Rr), allocation of feed energy differed among treatments and over time. Increases of somatic tissue (TTW) was highest in the T2 treatment (intermediate concentration), while Rr was highest in the T3 and T4 (highest concentration) treatments, but only after 14–21 days of supplementation. Within energy budgets, the highest proportion of feed energy was allocated to growth in all treatments (G; mean ± SE, 43.0 ± 3.1 %), followed by routine metabolic activities (Rr; mean ± SE, 26.12 ± 2.1 %). Overall, the mean net mass-specific cost of growth (cr) (mgO2l−1 g−1) was highest, and the net growth efficiency (% KN) was lowest, in the T3 and T4 treatments indicating that higher probiotic concentrations were related to higher allostatic loads (AL) compared to lower probiotic treatments (T1, T2). Overall, our results revealed that the proportion of C allocated to G and Rr varied differently with probiotic concentration, was tightly related to gut bacteria metabolic expenditures, and highlighted the importance of carefully evaluating the probiotic concentrations for optimization of growth performance in Mozambique tilapia aquaculture.

Inferring the metabolic rate of bone

Inferring the metabolic rate of bone

Brain energy metabolism as an underlying basis of slow and fast cognitive phenotypes in honeybees.

In the context of slow-fast behavioral variation, fast individuals are hypothesized to be those who prioritize speed over accuracy while slow individuals are those which do the opposite. Since energy metabolism is a critical component of neural and cognitive functioning, this predicts such differences in cognitive style to be reflected at the level of the brain. We tested this idea in honeybees by first classifying individuals into slow and fast cognitive phenotypes based on a learning assay and then measuring their brain respiration with high-resolution respirometry. Our results broadly show that inter-individual differences in cognition are reflected in differences in brain mass and accompanying energy use at the level of the brain and the whole animal. Larger brains had lower mass-specific energy usage and bees with larger brains had a higher metabolic rate. These differences in brain respiration and brain mass were, in turn, associated with cognitive differences, such that bees with larger brains were fast cognitive phenotypes whereas those with smaller brains were slow cognitive phenotypes. We discuss these results in the context of the role of energy in brain functioning and slow-fast decision making and speed accuracy trade-off.

Seasonal and between-population variation in heat tolerance and cooling efficiency in a Mediterranean songbird

Discrete populations of widely distributed species may inhabit areas with marked differences in climatic conditions across geographic and seasonal scales, which could result in intraspecific variation in thermal physiology reflecting genetic adaptation, phenotypic plasticity, or both. However, few studies have evaluated inter-population variation in physiological responses to heat. We evaluated within- and inter-population seasonal variation in heat tolerance, cooling efficiency and other key thermoregulatory traits in two Mediterranean populations of Great tit Parus major experiencing contrasting thermal environments: a lowland population subject to hotter summers and a higher annual thermal amplitude than a montane population. Specifically, we measured heat tolerance limits (HTL), body temperature, resting metabolic rate, evaporative water loss, and evaporative cooling efficiency (the ratio between evaporative heat loss to metabolic heat production) within and above the thermoneutral zone during winter and summer. Heat tolerance during summer was greater in lowland than in montane birds; indeed, lowland birds seasonally increased this trait to a significant level, while montane ones did to a lesser extent. Besides, lowland birds showed greater evaporative cooling efficiency during summer (possibly due in part to reductions in total endogenous heat load), while surprisingly montane ones showed the opposite trend. Thus, lowland birds displayed greater seasonal flexibility in HTL, body temperature and resting metabolic rate above thermoneutrality, thus giving some support to the climatic variability hypothesis — that flexibility in thermoregulatory traits should increase with climatic variability. Our results partially support the idea that songbirds’ adaptive thermoregulation in the heat is flexible, highlighting the importance of considering intraspecific variation in thermoregulatory traits when modelling the future distribution and persistence of species under different climate change scenarios.

The hydroperiod gradient drives species sorting in pace-of-life strategies but not in stressor sensitivity in Lestes damselfly larvae

Many species sort along environmental gradients, whereby species traits are predicted to shift as integrated sets of life-history, behavioural and physiological traits thereby making up a fast-to-slow pace-of-life continuum. This has also been predicted to cause species differences in stressor sensitivity along such gradients with a faster pace-of-life causing a higher sensitivity. We tested for predictable differences in pace-of-life and in stressor sensitivity for a set of four Lestes damselfly species that separate along the hydroperiod gradient. We reared in a common-garden experiment, larvae of two vernal pond specialists, L. dryas and L. barbarus, and two hydroperiod generalists, L. sponsa and L. virens, and exposed them to transient food deprivation and pesticide exposure, and monitored a set of life-history, behavioural and physiological traits both in the larvae and in the adults. Consistent with the time constraints imposed by the shorter hydroperiod of their habitat, the vernal pond specialists showed a faster pace-of-life (faster growth and development, and higher activity levels) than the hydroperiod generalists. Yet, in contrast with theory, this was not associated with a higher metabolic rate and a lower energy budget, neither with a higher oxidative damage to lipids. Both food deprivation and pesticide exposure were experienced as stressors, and species showed compensatory responses to cope with the transient food deprivation, including compensatory growth and delayed development. Nevertheless, the sensitivity to these stressors could not be predicted based on the difference in pace-of-life strategy between the vernal pond specialists and the hydroperiod generalists because of a decoupling of life-history and physiological traits. Our study indicates that while pace-of-life strategies change largely predictably along the hydroperiod gradient, these are not reliable predictors of species sensitivity to stressors. This highlights the need to consider also physiological traits to arrive at a generalizable predictive framework of species sensitivity to global change.

Targeted Temperature Management for Out-of-Hospital Cardiac Arrest Survivors.

Targeted temperature management (TTM), specifically therapeutic hypothermia, has been proposed to provide neuroprotective and mortality benefits for out-of-hospital cardiac arrest (OHCA) survivors. This proposition was based on small-scale trials from the early 2000s, leading to its incorporation into various international guidelines. The proposed neuroprotective mechanisms include reducing cerebral metabolic rate, stabilizing the blood-brain barrier, reducing the release of excitatory neurotransmitters, and suppressing apoptotic pathways. However, these early trials have been criticized for their high risk of bias and lack of standardized protocols. Recent evidence from more rigorously controlled randomized trials indicates no significant association between hypothermia and improved neurological outcomes or survival rates. This review explores the latest clinical evidence on TTM for OHCA patients, discussing the pathophysiology, evaluating the effectiveness of hypothermia through various clinical trials, and providing recommendations for future research and clinical practice.

Impaired insulin sensitivity measured by estimated glucose disposal rate is associated with decreased myocardial mechano-energetic efficiency in non-diabetic individuals

Background and aimsImpaired myocardial mechano-energetic efficiency (MEE) has been associated with cardiac insulin resistance measured by dynamic positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) combined with euglycemic–hyperinsulinemic clamp. Estimate glucose disposal rate (eGDR) index has a good correlation with whole-body insulin sensitivity. It remains unsettled whether eGDR index is a suitable proxy of cardiac insulin sensitivity as well as its association with myocardial MEE. The aims of this study were: 1) to compare eGDR index with HOMA-IR, QUICKI and FIRI indexes for association with myocardial glucose metabolic rate (MrGlu); and 2) to determine the association of eGDR index with myocardial MEE. MethodsWe evaluated MrGlu using PET with 18F-FDG combined with euglycemic–hyperinsulinemic clamp in 50 individuals without history of coronary heart disease. Myocardial MEE per gram of left ventricular mass (MEEi) was measured in 1181 subjects by echocardiography. eGDR (mg kg-1/min) was calculated as: 21.158 - (0.09 × waist circumference in cm) - (3.407 × hypertension, 1 = yes 0 = no) - (0.551 × HbA1c%). ResultseGDR index was more strongly associated with myocardial MrGlu than HOMA-IR, QUICKI, and FIRI indexes (r = -0.662, r = -0.492, r = 0.570, and r = -0.492, respectively). Individuals in the lower tertiles of eGDR exhibited a significant reduction of MEEi as compared to those in the highest tertile (P < 0.001). In a stepwise multivariate linear regression analysis eGDR index was the major determinant of MEEi independently of well-established cardio-metabolic risk factors. ConclusionsThese data suggest that the eGDR index may be a useful marker to identifying individuals at high cardiovascular risk.

Comparative analysis of basal metabolic rate measurement methods in overweight and obese individuals: A retrospective study.

The global prevalence of overweight and obesity is on the rise, presenting significant health challenges worldwide. Obesity is associated with various chronic diseases and imposes substantial economic burdens on society. Accurate assessment of basal metabolic rate (BMR) is crucial for effective weight management strategies. This retrospective study, conducted at Baskent University Hospital between October 2019 and October 2023, analyzed data from 133 overweight and obese individuals. Various methods including indirect calorimetry (IC), predictive equations (Harris-Benedict and Mifflin-St Jeor), and bioelectrical impedance analysis (BIA) were used to estimate BMR. Additionally, demographic, clinical, and body composition data were recorded. The mean BMR measured using IC was 1581 ± 322 kcal/day, which was significantly lower than the BMR estimated by other methods such as BIA (1765.8 ± 344.09 kcal/day), Harris-Benedict (1787.64 ± 341.4 kcal/day), and Mifflin-St Jeor equations (1690.08 ± 296.36 kcal/day) (P < .001). Among the predictive equations, the Mifflin-St Jeor method provided BMR estimates closest to the gold standard IC. When BMR measurement methods were compared to IC, 36.8% of measurements with the Harris-Benedict equation method, 50.4% with the Mifflin-St Jeor equation method, and 36.1% with the BIA method were within ± 10% agreement with IC measurements. Significant correlations were found between BMR and body composition parameters such as fat-free mass, muscle mass, and fat mass (R = 0.681, P < .001; R = 0.699, P < .001; R = 0.595, P < .001, respectively). Regression analysis identified that variables such as weight, height, body mass index, and muscle mass significantly predicted BMR measured by IC, accounting for 69.1% of the variance. This study underscores the challenges in assessing BMR in overweight and obese individuals. While IC remains the gold standard, predictive equations and BIA offer alternative methods. The Mifflin-St Jeor equation emerged as a practical option, closely aligning with IC results. However, discrepancies between methods and the influence of body composition highlight the importance of individualized approaches to BMR assessment in weight management strategies.

Physiological and behavioral responses to social isolation and starvation in a social fish

Changes in the social environment, such as segregating an individual who would typically reside within a social group, may elicit physiological and behavioral responses to external stimulus such as starvation. However, such changes in phenotypic traits receive a little attention in social fish. Here, we used qingbo (Spinibarbus sinensis) with high level of sociability as animal model in order to examine the physiological and behavioral responses of this fish species to social environment (isolation vs. grouping) and nutritional state (well-fed vs. starvation). We found that differences in the reduction of body masses between the group-reared and the isolation-reared fish during periods of starvation can be partially attributed to variations in water volume within the tanks. Additionally, the decrease in standard metabolic rate was more pronounced in the group-reared fish compared to the isolation-reared fish when deprived of food, except for maximum metabolic rate and aerobic scope. Interestingly, only the group-reared fish experienced a decline in constant acceleration swimming performance after food deprivation, while this was not observed in the isolated fish. Neither social isolation nor starvation had any impact on personality expression (e.g., exploration, activity, and boldness). However, both exploration and boldness exhibited temporal effects with an increase in these two personality traits. Social isolation tended to elevate anxiety-like behavior levels. Both social isolation and starvation did not affect upper thermal tolerance; however, starvation enhanced cold resistance of the fish. Our findings contribute to a better understanding of how social environment combined with trophic stress influences phenotypic traits and may offer valuable insights into animal welfare considerations for both natural habitats and aquaculture practices.

Temperature-dependent in vitro hepatocytotoxicity of insecticides in bats

Heterothermic insectivorous bats are supposed to experience differential adverse effects of insecticidal pollutants depending on their seasonal and/or daily variation of metabolic and detoxification rates. Here, we investigated effects of imidacloprid, cypermethrin and fipronil on Nyctalus noctula bat-derived hepatocytes through cytotoxicity, cell inhibition and death at different concentrations (0.01, 0.1, 1, 10, 100, 1000 μg/ml), exposure times (10, 24, 48 hrs), incubation temperatures simulating hibernation (8 °C), daily torpor (20 °C), normothermy (37 °C) and active flight (40 °C), and cytochrome P450 addition. Toxic effects were significantly influenced by temperature (p < 0.05), with strong cytotoxicity after 10 hour exposure to fipronil or cypermethrin at 37 and 40 °C, cell replication inhibition (all insecticides at 8 °C) and cellular stimulation, with slight culture proliferation after 48 hours (all insecticides at 40 °C). Replacing protected chiropterans with cell cultures is a way to assess and extrapolate risks of insecticides for bats.

No effect of circulating leptin on energy metabolism in normal weight or overweight/obese lactating mothers: The case-control Breastmilk and the Link to Overweight/Obesity and Maternal diet (BLOOM) study

Pregnancy and lactation are associated with metabolic changes, including alterations in energy metabolism, which are closely linked to body mass and composition due to hormonal status. Therefore, the objective of this study was to investigate the energy metabolism in exclusively or predominantly breastfeeding mothers with normal weight (NW) and overweight/obesity (OW/OB) and evaluate its associations with fasting serum leptin. This cross-sectional BLOOM study was conducted among 39 mothers (N=19 NW, N=20 OW/OB) in 15.5±1.2 weeks of lactation. The leptin was analyzed in a blood sample using an enzyme-linked immunosorbent assay, body composition was analyzed by dual-energy X-ray absorptiometry, and resting metabolic rate (RMR) was measured by indirect calorimetry method. The average RMR for all groups was 1747.5 ± 281.9 kcal/d, with a statistically significant difference between groups (1932.7 ± 222.6 vs. 1550.5 ± 190.6, p<0.001, respectively in the OW/OB and NW group). The OW/OB mothers had higher oxygen uptake (VO2) and exhaled carbon dioxide (VCO2), but not respiratory quotient (RQ), carbohydrate (CHO%) and lipid oxidation (FAT%). When analyzing correlations stratified by BMI category, we found that serum leptin was correlated with CHO% negatively, and with FAT% positively in the NW but not in OW/OB mothers. Additionally, serum leptin was a significant predictor of RMR, VCO2, VO2, CHO%, and RMR/kg of total body weight. However, after adjusting for confounders, the observed associations were no longer statistically significant (RMR: β=0.113, 95% CI -0.354 - 0.319; VO2: β=0.141, 95% CI -0.462 - 0.744; VCO2: β=0.238, 95% CI -0.411 - 0.888; CHO%: β=-0.146, 95% CI -0.151 - 0.444; RMR/kg of total body weight: β= -0.294, 95% CI -0.831 - 0.244). Our results did not support the hypothesis that leptin plays a role in regulating energy homeostasis during lactation.

Divergent metabolism estimates from dissolved oxygen and inorganic carbon: Implications for river carbon cycling

AbstractRivers efficiently collect, process, and transport terrestrial‐derived carbon. River ecosystem metabolism is the primary mechanism for processing carbon. Diel cycles of dissolved oxygen (DO) have been used for decades to infer river ecosystem metabolic rates, which are routinely used to predict metabolism of carbon dioxide (CO2) with uncertainties of the assumed stoichiometry ranging by a factor of 4. Dissolved inorganic carbon (DIC) has been less used to directly infer metabolism because it is more difficult to quantify, involves the complexity of inorganic carbon speciation, and as shown in this study, likely requires a two‐station approach. Here, we developed DIC metabolism models using single‐ and two‐station approaches. We compared metabolism estimates based on simultaneous DO and DIC monitoring in the Upper Clark Fork River (USA), which also allowed us to estimate ecosystem‐level photosynthetic and respiratory quotients (PQE and RQE). We observed that metabolism estimates from DIC varied more between single‐ and two‐station approaches than estimates from DO. Due to carbonate buffering, CO2 is slower to equilibrate with the atmosphere compared to DO, likely incorporating a longer distance of upstream heterogeneity. Reach‐averaged PQE ranged from 1.5 to 2.0, while RQE ranged from 0.8 to 1.5. Gross primary production from DO was larger than that from DIC, as was net ecosystem production by . The river was autotrophic based on DO but heterotrophic based on DIC, complicating our understanding of how metabolism regulated CO2 production. We suggest future studies simultaneously model metabolism from DO and DIC to understand carbon processing in rivers.

Chronic cold exposure causes left ventricular hypertrophy that appears to be physiological.

Exposure to winter cold causes an increase in energy demands to meet the challenge of thermoregulation. In small rodents, this increase in cardiac output leads to a profound cardiac hypertrophy, 2-3x that typically seen with exercise training. The nature of this hypertrophy and its relevance to winter mortality remains unclear. Our goal was to characterize cold-induced cardiac hypertrophy and to assess its similarity to either exercise-induced (physiological) hypertrophy or the pathological hypertrophy of hypertension. We hypothesized that cold-induced hypertrophy will most closely resemble exercise-induced hypertrophy, but be another unique pathway for physiological cardiac growth. We found that cold-induced hypertrophy was largely reversed after return to warm temperatures. Further, metabolic rates were elevated while gene expression and mitochondrial enzyme activities indicative of pathology were absent. A gene expression panel comparing hearts of exercised and cold exposed mice further suggests that these activities are similar, although not identical. In conclusion, we found that chronic cold led to a phenotype that most closely resembled physiological hypertrophy, with enhanced metabolic rate, without induction of fetal genes , but with decreased expression of genes associated with fatty acid oxidation, suggesting that heart failure is not a cause of winter mortality in small rodents and identifying a novel approach for the study of cardiac growth.

Association between change in heart rate over years and life span in the Paris Prospective 1, the Whitehall 1, and Framingham studies.

Heart rate, a measure of the frequency of the cardiac cycle, reflects the health of the cardiovascular system, metabolic rate, and activity of the autonomic nervous system. Whether changes in resting heart rate are related to lifespan has not yet been explored to our best knowledge. In this study, we examined the association between resting heart rate and lifespan using linear regression in the Paris Prospective Study I, the Whitehall I Study, and the Framingham Heart Study. We used Cox proportional hazards regression to relate changes in heart rate over years to mortality risk. We observed a statistically significant association between increases in resting heart rate over a 5-year period and risk of mortality in the Paris Prospective Study I (HR mortality per 10 bpm increase over time: 1.20; 95% CI: 1.13 to 1.27) and over an 8-year period in the Framingham Heart Study (HR: 1.13; 95% CI: 1.07 to 1.19 for men and HR: 1.09; 95% CI: 1.04 to 1.15 for women), after adjusting for classical risk factors and resting heart rate. Our study shows that men and women who increase their resting heart rate over time increase their risk of mortality.