American Journal of Physiology. Regulatory, Integrative and Comparative Physiology

This single-blind, crossover study aimed to measure and evaluate the short-term metabolic responses to continuous and intermittent hypoxic patterns in individuals with obesity. Indirect calorimetry was used to quantify changes in resting metabolic rate (RMR), carbohydrate (CHOox , %CHO) and fat oxidation (FATox , %FAT) in nine individuals with obesity pre- and post-: (i) breathing normoxic air [normoxic sham control (NS-control)]; (ii) breathing continuous hypoxia (CH); or (iii) breathing intermittent hypoxia (IH)...

Although Gaussian white noise (GWN) inputs offer a theoretical framework for identifying higher-order nonlinearity, an actual application to the data of the neural arc of the carotid sinus baroreflex did not succeed in fully predicting the well-known sigmoidal nonlinearity. In the present study, we assumed that the neural arc can be approximated by a cascade of a linear dynamic (LD) component and a nonlinear static (NS) component. We analyzed the data obtained using GWN inputs with a mean of 120 mmHg and standard deviations (SDs) of 10, 20, and 30 mmHg for 15 min each in anesthetized rats (n = 7)...

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Muscle mass is balanced between hypertrophy and atrophy by cellular processes, including activation of the protein kinase B-mechanistic target of rapamycin (Akt-mTOR) signaling cascade. Stressors apart from exercise and nutrition, such as heat stress, can stimulate the heat shock protein A (HSPA) and C (HSPC) families alongside hypertrophic signaling factors and muscle growth. The effects of heat stress on HSP expression and Akt-mTOR activation in human skeletal muscle and their magnitude of activation compared with known hypertrophic stimuli are unclear...

Exercise intolerance is a hallmark symptom of heart failure and to a large extent stems from reductions in cardiac output that occur due to the inherent ventricular dysfunction coupled with enhanced muscle metaboreflex-induced functional coronary vasoconstriction which limits increases in coronary blood flow. This creates a further mismatch between O2 delivery and O2 demand which may activate the Cardiac Sympathetic Afferent Reflex (CSAR) causing amplification of the already increased sympathetic activity in a positive-feedback fashion...

Laboratory mice are commonly used for studies emulating human metabolism. To render human energetics, their ratio of daily (DEE) to basal (BMR) energy expenditure of 1.7-1.8 should be maintained. However, the DEE/BMR ratio strongly depends on whether a given study utilizing a mouse model is carried out above, or below the lower critical temperature (LCT) of the thermoneutral zone, which is rarely considered in translational research. Here, we used mice artificially selected for high or low rates of BMR along with literature data to analyse the effect of ambient temperature on possible systematic bias in DEE/BMR...

Certain deep-diving marine mammals (i.e., northern elephant seal ( Mirounga angustirosis ), Weddell seal ( Leptonychotes weddellii )) have blood carbon monoxide (CO) levels that are comparable to those of chronic cigarette smokers. Most CO produced in humans is a by-product of heme degradation, which is released when red blood cells (RBC) are destroyed. Elevated CO can occur in humans when RBC lifespan decreases. The contribution of RBC turnover to CO concentrations in marine mammals is unknown. Here, we report the first RBC lifespans in two healthy, marine mammal species with different diving capacities and heme stores, the shallow diving bottlenose dolphin ( Tursiops truncatus ) and deep-diving beluga ( Delphinapterus leucas ), and relate the lifespans to the levels of CO in blood and breath...

To maintain heat balance during exercise, humans rely on skin blood flow and sweating to facilitate whole-body dry and evaporative heat exchange. These responses are modulated by the rise in body temperature (thermal factors), as well as several non-thermal factors implicated in the cardiovascular response to exercise (i.e., central command, mechanoreceptors, metaboreceptors). However, the way these non-thermal factors interact with thermal factors to maintain heat balance remains poorly understood. We therefore used direct calorimetry to quantify the effects of dose-dependent increases in the activation of these non-thermal stimuli on whole-body dry and evaporative heat exchange during dynamic exercise...

In addition to its role in substrate selection (carbohydrate vs. fat) for oxidative metabolism in muscle, acetylcarnitine production may be an important modulator of the energetic pathway by which ATP is produced. A combination of noninvasive magnetic resonance spectroscopy measures of cytosolic acetylcarnitine and ATP production pathways was used to investigate the link between [acetylcarnitine] and energy production in vivo . Intracellular metabolites were measured in the vastus lateralis muscle of 8 males (mean 28...

Autophagy is a vital cellular process, essential to maintaining cellular function during acute physiological stressors including exercise and heat stress. We previously showed that autophagy occurs during exercise in an intensity-dependent manner in peripheral blood mononuclear cells (PBMCs) from young men, with elevated responses in the heat. However, given autophagy declines with age, it is unclear whether a similar pattern of response occurs in older adults. Therefore, we evaluated autophagy and the cellular stress response (i...

Maternal obesity increases the risk of adverse pregnancy outcomes. The mechanisms that contribute to this elevated risk are unclear but may be related to greater activity of the sympathetic nervous system, which is associated with hypertensive disorders of pregnancy. We hypothesized that resting muscle sympathetic nerve activity (MSNA) would be greater in women with obesity during pregnancy when compared with normal-weight women. Blood pressure, heart rate and MSNA were recorded during 5 min of supine rest in 14 normal-weight women (body mass index [BMI] 22...

Asthma is a disorder of the airways characterized by chronic airway inflammation, hyperresponsiveness, and variable recurring airway obstruction. Treatment options for asthma include pharmacological strategies, whereas nonpharmacological strategies are limited. Established pharmacological approaches to treating asthma may cause unwanted side effects and do not always afford adequate protection against asthma, possibly because of an individual's variable response to medications. A potential nonpharmacological intervention that is most available and cost effective is inspiratory muscle training (IMT), which is a technique targeted at increasing the strength and endurance of the diaphragm and accessory muscles of inspiration...

Identification of the breathing cycle forms the basis of any breath-by-breath gas exchange analysis. Classically, the breathing cycle is defined as the time interval between the beginning of two consecutive inspiration phases. Based on this definition, several research groups have developed algorithms designed to estimate the volume and rate of gas transferred across the alveolar membrane ("alveolar gas exchange"); however, most algorithms require measurement of lung volume at the beginning of the i th breath ( VLi- 1 ; i...

BACKGROUND: Whole-body exercise provides protection against endothelial ischemia-reperfusion (IR) injury. In this crossover study, we examined the effects of 1) single bout of local exercise (handgrip, squats) on endothelial responses to IR , and 2) if 7 days of daily exercise bolsters these effects in individuals with cardiovascular disease (CVD) risk factors. METHODS: Fifteen participants (9 women, 58±5 years, ≥2 CVD risk factors) attended the laboratory for 6 visits...

Cannabidiol (CBD) use has grown exponentially more popular in the last two decades, particularly amongst older adults (>55 years), though very little is known about the effects of CBD use during age-associated metabolic dysfunction. Additionally, synthetic analogues of CBD have generated great interest because they can offer a chemically pure product, which is free of plant-associated contaminants. To assess the effects of a synthetic analogue of CBD (H4CBD) on advanced metabolic dysfunction, a cohort of 41-week-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats were administered 200 mg H4CBD/kg by oral gavage for 4 weeks...

Hydrogen peroxide (H2 O2 ) and calcium ions (Ca2+ ) are functional regulators of skeletal muscle contraction and metabolism. Although H2 O2 is one of the activators of the type-1 ryanodine receptor (RyR1) in the Ca2+ release channel, the interdependence between H2 O2 and Ca2+ dynamics remains unclear. This study tested the following hypotheses using an in vivo model of mouse tibialis anterior (TA) skeletal muscle. 1. Under resting conditions, elevated cytosolic H2 O2 concentration ([H2 O2 ]cyto ) leads to a concentration-dependent increase in cytosolic Ca2+ concentration ([Ca2+ ]cyto ) through its effect on RyR1...

INTRODUCTION: There is growing interest in how breathing pace, pattern, and training (e.g., device-guided or -resisted breathing) affect cardiovascular health. It is unknown whether the route of breathing (nasal versus oral) affects prognostic cardiovascular variables. Because nasal breathing can improve other physiological variables (e.g., airway dilation), we hypothesized that nasal compared with oral breathing would acutely lower blood pressure (BP) and improve heart rate variability (HRV) metrics...

Moderate-to-heavy episodic ("binge") drinking is the most common form of alcohol consumption in the United States. Alcohol at binge drinking concentrations reduces brain artery diameter in vivo and in vitro in many species including rats, mice and humans. Despite the critical role played by brain vessels in maintaining neuronal function, there is a shortage of methodologies to simultaneously assess neuron and blood vessel function in deep brain regions. Here, we investigate cerebrovascular responses to ethanol by choosing a deep brain region that is implicated in alcohol-disruption of brain function, the hippocampal CA1, and describe the process for obtaining simultaneous imaging of pyramidal neuron activity and diameter of nearby microvessels in freely moving mice via a dual-color miniscope...

The sleep-wake cycle of human subjects was artificially split into two episodes by imposing an 8-h light and 4-h dark cycle (LD 8:4) twice a day for 7 days, which was followed by a 3 day free-running session. Sleep was permitted only in the dark period. The subjects in the ordinary group were exposed to ordinary light (ca. 500 lux) in the 8-h light period, and those in the bright light group to bright (ca. 5,000 lux) and ordinary light alternatively with bright light after the 1st dark period (24:00 - 4:00 h)...

The oviduct of the Chinese brown frog (Rana dybowskii) expands in pre-hibernation rather than in pre-spawning, which is one of the physiological phenomena that occur in preparation for hibernation. Steroid hormones are known to regulate oviductal development. Cholesterol synthesis and steroidogenesis may play important role in the expansion of the oviduct before hibernation. In this study, we investigated the expression patterns of the markers that are involved in the de novo steroid synthesis pathway in the oviduct of R...