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In the USA, as many as 20 % of recruits sustain stress fractures during basic training. In addition, approximately one-third of female recruits develop Fe deficiency upon completion of training. Fe is a cofactor in bone collagen formation and vitamin D activation, thus we hypothesised Fe deficiency may be contributing to altered bone microarchitecture and mechanics during 12-weeks of increased mechanical loading. Three-week old female Sprague Dawley rats were assigned to one of four groups: Fe-adequate sedentary, Fe-deficient sedentary, Fe-adequate exercise and Fe-deficient exercise. Exercise consisted of high-intensity treadmill running (54 min 3×/week). After 12-weeks, serum bone turnover markers, femoral geometry and microarchitecture, mechanical properties and fracture toughness and tibiae mineral composition and morphometry were measured. Fe deficiency increased the bone resorption markers C-terminal telopeptide type I collagen and tartate-resistant acid phosphatase 5b (TRAcP 5b). In exercised rats, Fe deficiency further increased bone TRAcP 5b, while in Fe-adequate rats, exercise increased the bone formation marker procollagen type I N-terminal propeptide. In the femur, exercise increased cortical thickness and maximum load. In the tibia, Fe deficiency increased the rate of bone formation, mineral apposition and Zn content. These data show that the femur and tibia structure and mechanical properties are not negatively impacted by Fe deficiency despite a decrease in tibiae Fe content and increase in serum bone resorption markers during 12-weeks of high-intensity running in young growing female rats.

Objective Carbon monoxide (CO) may counteract obesity and metabolic dysfunction in rodents consuming high-fat diets, but the skeletal effects are not understood. This study investigated whether low-dose inhaled CO (250 ppm) with or without moderate intensity aerobic exercise (3 h/wk) would limit diet-induced obesity and metabolic dysregulation and preserve bone health. Methods Obesity-resistant (OR) rats served as controls, and obesity-prone (OP) rats were randomized to sedentary, sedentary plus CO, exercise, or CO plus exercise. For 10 weeks, OP rats consumed a high-fat, high-sucrose diet, whereas OR rats consumed a low-fat control diet. Measurements included indicators of obesity and metabolism, bone turnover markers, femoral geometry and microarchitecture, bone mechanical properties, and tibial morphometry. Results A high-fat, high-sucrose diet led to obesity, hyperinsulinemia, and hyperleptinemia, without impacting bone. CO alone led only to a modest reduction in weight gain. Exercise attenuated weight gain and improved the metabolic profile; however, bone fragility increased. Combined CO and exercise led to body mass reduction and a metabolic state similar to control OR rats and prevented the exercise-induced increase in bone fragility. Conclusions CO and aerobic exercise training prevent obesity and metabolic sequelae of nutrient excess while stabilizing bone physiology.

Inducible heme oxygenase (HO)-1 catalyzes the breakdown of heme to biliverdin, iron, and carbon monoxide (CO). CO binds to cytochrome c oxidase and alters mitochondrial redox balance and coordinately regulates mitochondrial quality control (MQC) during oxidant stress and inflammation. The hypothesis presented is that the skeletal muscle HO-1/CO system helps modulate components in the MQC cycle during metabolic stress.

Stress fractures are common overuse injuries caused by repetitive bone loading. These fractures are of particular concern for military recruits and athletes resulting in attrition in up to 60% of recruits that sustain a fracture. Army and Navy recruits supplemented with daily calcium and vitamin D (Ca + D) demonstrated improved bone strength and reduced stress fractures. The aim of the current study was to evaluate whether Ca + D supplementation improves measures of bone health in recruits undergoing United States Marine Corps initial military training (IMT), and whether the effect of supplementation on indices of bone health varied by season. One-hundred ninety-seven Marine recruits (n = 107 males, n = 90 females, mean age = 18.9 ± 1.6 y) were randomized to receive either Ca + D fortified snack bars (2000 mg Ca and 1000 IU vitamin D per day) or placebo divided into twice daily doses during 12 weeks of IMT. Anthropometrics, fasted blood samples, and peripheral quantitative computed tomography (pQCT) scans of the tibial metaphysis and diaphysis were collected upon entrance to- and post-training (12 weeks later). Half of the volunteers entered training in July and the other half started in February. Time-by-group interactions were observed for vitamin D status (25OHD) and the bone turnover markers, BAP, TRAP and OCN. 25OHD increased and BAP, TRAP and OCN all decreased in the Ca + D group (p .05). Training increased distal tibia volumetric BMD (+1.9 ± 2.8%), BMC (+2.0 ± 3.1%), and bone strength index (BSI; +4.0 ± 4.0%) and diaphyseal BMC (+1.0 ± 2.2%) and polar stress strain index (SSIp; +0.7 ± 2.1%) independent of Ca + D supplementation (p .05 for all). When analyzed by season, change in BSI was greater in the Ca + D group as compared to placebo in the summer iteration only (T*G; p .05). No other effects of supplementation on bone tissue were observed. When categorized by tertile of percent change in BSI, recruits demonstrating the greatest changes in BSI and 25OHD entered training with the lowest levels of 25OHD (p .05). Over all, these results suggest that Ca + D supplementation reduced some markers of bone formation and resorption and the decline in 25OHD over training in volunteers that started training in the summer was prevented by supplementation. Baseline 25OHD and trajectory may impact bone responses to IMT, but little effect of Ca + D supplementation was observed at the investigated doses.

Heat stress causes mitochondrial dysfunction and increases mitochondrial production of reactive oxygen species (ROS), both of which contribute to heat-induced skeletal muscle injury. In this study, we tested whether either astaxanthin or quercetin, two dietary antioxidants, could ameliorate heat-induced skeletal muscle oxidative injury. In mouse C2C12 myoblasts exposed to 43°C heat stress, astaxanthin inhibited heat-induced ROS production in a concentration-dependent manner (1-20 μM), whereas the ROS levels remained high in cells treated with quercetin over a range of concentrations (2-100 µM). Because mitochondria are both the main source and a primary target of heat-induced ROS, we then tested the effects of astaxanthin and quercetin on mitochondrial integrity and function, under both normal temperature (37°C) and heat stress conditions. Quercetin treatment at 37°C induced mitochondrial fragmentation and decreased membrane potential (ΔΨ m ), accompanied by reduced protein expression of the master regulator of mitochondrial biogenesis peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). It also induced cleavage of mitochondrial inner-membrane fusion protein OPA1. In contrast, astaxanthin at 37°C increased protein expression of PGC-1α and mitochondrial transcription factor A (TFAM), and maintained tubular structure and normal ΔΨm . Under 43°C heat stress conditions, whereas quercetin failed to rescue C2C12 cells from injury, astaxanthin treatment prevented heat-induced mitochondrial fragmentation and depolarization, and apoptotic cell death. We also isolated rat flexor digitorum brevis myofibers and confirmed the data from C2C12 myoblasts that astaxanthin but not quercetin preserves mitochondrial integrity and function and ameliorates heat-induced skeletal muscle injury. These results confirm that mitochondria may be a potential therapeutic target for heat-related illness and suggest that astaxanthin may potentially be an effective preventive strategy.

Nutrient excess increases skeletal muscle oxidant production and mitochondrial fragmentation that may result in impaired mitochondrial function, a hallmark of skeletal muscle insulin resistance. This led us to explore whether an endogenous gas molecule, carbon monoxide (CO), which is thought to prevent weight gain and metabolic dysfunction in mice consuming high-fat diets, alters mitochondrial morphology and respiration in C2C12 myoblasts exposed to high glucose (15.6 mM) and high fat (250 µM BSA-palmitate) (HGHF). Also, skeletal muscle mitochondrial morphology, distribution, respiration, and energy expenditure were examined in obese resistant (OR) and obese prone (OP) rats that consumed a high-fat and high-sucrose diet for 10 wk with or without intermittent low-dose inhaled CO and/or exercise training. In cells exposed to HGHF, superoxide production, mitochondrial membrane potential (ΔΨm), mitochondrial fission regulatory protein dynamin-related protein 1 (Drp1) and mitochondrial fragmentation increased, while mitochondrial respiratory capacity was reduced. CO decreased HGHF-induced superoxide production, Drp1 protein levels and mitochondrial fragmentation, maintained ΔΨm, and increased mitochondrial respiratory capacity. In comparison with lean OR rats, OP rats had smaller skeletal muscle mitochondria that contained disorganized cristae, a normal mitochondrial distribution, but reduced citrate synthase protein expression, normal respiratory responses, and a lower energy expenditure. The combination of inhaled CO and exercise produced the greatest effect on mitochondrial morphology, increasing ADP-stimulated respiration in the presence of pyruvate, and preventing a decline in resting energy expenditure. These data support a therapeutic role for CO and exercise in preserving mitochondrial morphology and respiration during metabolic overload.

BACKGROUND: Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and the mitochondrial electron transport chain are the primary sources of reactive oxygen species (ROS). Previous studies have shown that severe heat exposure damages mitochondria and causes excessive mitochondrial ROS production that contributes to the pathogenesis of heat-related illnesses. OBJECTIVES: We tested whether the antioxidant curcumin could protect against heat-induced mitochondrial dysfunction and skeletal muscle injury, and characterized the possible mechanism. METHODS: Mouse C2C12 myoblasts and rat flexor digitorum brevis (FDB) myofibers were treated with 5 μM curcumin; adult male C57BL/6J mice received daily curcumin (15, 50, or 100 mg/kg body weight) by gavage for 10 consecutive days. We compared ROS levels and mitochondrial morphology and function between treatment and nontreatment groups under unheated or heat conditions, and investigated the upstream mechanism and the downstream effect of curcumin-regulated ROS production. RESULTS: In C2C12 myoblasts, curcumin prevented heat-induced mitochondrial fragmentation, ROS overproduction, and apoptosis (all P

Aims The interplay between hyper-glycemia and -lipidemia in diabetes mellitus (DM) is important in simulating diabetic conditions. However, cell culture media typically contain supraphysiological levels of glucose to stimulate cellular growth, which also desensitizes cells to elevated glucose levels. Moreover, creating hyperlipidemic conditions in vitro requires specialized carriers because unbound lipids form micelles when introduced to liquid media. This study sought to develop a novel method for simulating DM conditions in vitro. Materials and methods We acclimated the C2C12 mouse myoblasts to culture medium with 5.6 mM glucose, which mimics physiological levels, and created a bovine serum albumin-palmitic acid conjugate for lipid transport to explore the effects of hyperlipidemia. We simulated diabetic conditions in vitro by using both hyper–glycemic and –lipidemic conditions and compared the results to that of only hyperglycemic or hyperlipidemic conditions. Key findings Acclimated cells exposed to these hyper-glycemic (15 mM glucose) and/or -lipidemic (0.25 mM palmitate) conditions for 2 h showed increased mitochondrial fragmentation and membrane potential as well as elevated reactive oxygen species production compared to control cells. These findings suggest altered mitochondrial morphology and function, which have been confirmed using isolated rat flexor digitorum brevis myofibers. Hyper-glycemic and/or -lipidemic stimulations for 24 h significantly increased mitogen-activated protein kinase kinase MEK 1/2 protein expression, upregulated the early pro-apoptotic transcription factor C/EBP homologous protein (CHOP), and induced apoptosis. Significance Our results further support and confirm the utility of this method which will allow for subsequent investigations studying the effects of hyper-glycemia and/or -lipidemia in vitro.

A reduction in oxygen transport contributes to impaired exercise capacity at high altitude. Since blood flow is mediated, in part, by nitric oxide (NO), we hypothesized that sodium nitrate provided before forearm grip exercise performed at a simulated altitude of 4300 m (hypobaric hypoxia (HH)) would increase forearm blood flow and oxygenation, and decrease the decrement in grip performance. In a double-blind, randomized crossover study, 10 healthy subjects (9 males and 1 female) performed continuous (CGrip) and repeated rhythmic (RGrip) isometric forearm exercise until task failure in normobaric normoxia (NN), 2.5 h following consumption of placebo and sodium nitrate (15 mmol) in HH, and then again post-HH at sea-level pressure. Measurements included forearm blood flow (FBF) and anterior forearm tissue oxygenation (StO2), mean arterial blood pressure (MAP), arterial blood O2 saturation (SpO2), plasma NO reaction products (NOx) and nitrite, and exhaled NO (PENO). Compared to baseline testing in NN, performing CGrip and RGrip exercise in HH resulted in significant reductions in forearm blood flow, SaO2 and StO2, responses that were accompanied by significant performance decrements (∼10%) in both CGrip and RGrip exercise. In spite of a 10-fold increase in plasma NOx levels and a significant decrease in MAP during CGrip exercise following nitrate consumption, there were no significant main effects of treatment (placebo vs. sodium nitrate) for forearm blood flow, SpO2, StO2, or grip performance. PENO remained unchanged between NN, HH and post-HH conditions with placebo, but increased (∼24%) following nitrate supplementation in HH and post-HH. These data do not support a benefit in consuming a single dose of supplemental nitrate on forearm blood flow and isometric exercise in healthy adults at a simulated altitude of 4300 m.

Breathing oxygen at partial pressures ≥2.5 atmospheres absolute, which can occur in diving and hyperbaric oxygen (HBO2) therapy, can rapidly become toxic to the central nervous system (CNS). This neurotoxicity culminates in generalized EEG epileptiform discharges, tonic-clonic convulsions and ultimately death. Increased production of neuronal nitric oxide (NO) has been implicated in eliciting hyperoxic seizures by altering the equilibrium between glutamatergic and GABAergic synaptic transmission. Inhibition of glutamic acid decarboxylase (GAD) activity in HBO2 promotes this imbalance; however, the mechanisms by which this occurs is unknown. Therefore, we conducted a series of experiments using mice, a species that is highly susceptible to CNS oxygen toxicity, to explore the possibility that NO modulates GABA metabolism. Mice were exposed to 100% oxygen at 4 ATA for various durations, and brain GAD and GABA transaminase (GABA-T) activity, as well as S-nitrosylation of GAD65 and GAD67 were determined. HBO2 inhibited GAD activity by 50% and this was negatively correlated with S-nitrosylation of GAD65, whereas GABA-T activity and S-nitrosylation of GAD67 were unaltered. These results suggest a new mechanism by which NO alters GABA metabolism, leading to neuroexcitation and seizures in HBO2.

Hyperbaric oxygen (HBO2) is acutely toxic to the central nervous system, culminating in EEG spikes and tonic-clonic convulsions. GABA enhancers and sodium channel antagonists improve seizure latencies in HBO2 when administered individually, while combining antiepileptic drugs from different functional classes can provide greater seizure latency. We examined the combined effectiveness of GABA enhancers (tiagabine and gabapentin) with sodium channel antagonists (carbamazepine and lamotrigine) in delaying HBO2-induced seizures. A series of experiments in C57BL/6 mice exposed to 100% oxygen at 5 atmospheres absolute (ATA) were performed. We predicted equally effective doses from individual drug-dose response curves, and the combinations of tiagabine + carbamazepine or lamotrigine were tested to determine the maximally effective combined doses to be used in subsequent experiments designed to identify the type of pharmacodynamic interaction for three fixed-ratio combinations (1:3, 1:1, and 3:1) using isobolographic analysis. For both combinations, the maximally effective combined doses increased seizure latency over controls > 5-fold and were determined to interact synergistically for fixed ratios 1:1 and 3:1, additive for 1:3. These results led us to explore whether the benefits of these drug combinations could be extended to the lungs, since a centrally mediated mechanism is believed to mediate hyperoxic-induced cardiogenic lung injury. Indeed, both combinations attenuated bronchoalveolar lavage protein content by ~ 50%. Combining tiagabine with carbamazepine or lamotrigine not only affords greater antiseizure protection in HBO2 but also allows for lower doses to be used, minimizing side effects, and attenuating acute lung injury.

Vitamin D's role in regulating immune responses may increase during periods of elevated psychological and physiological stress. Due to the high demands placed on US Marine Corps recruits undergoing 12 weeks of basic military training, we hypothesized that vitamin D status would be related to markers of innate mucosal immunity, and daily vitamin D supplementation would augment immune responses during training. Males (n = 75) and females (n = 74) entering recruit basic training during the summer and winter volunteered to participate in a randomized, double-blind, placebo-controlled study. Subjects received either 1000 IU vitamin D3 + 2000 mg calcium/d (n = 73) or placebo (n = 76) for 12 weeks. Saliva samples were collected pre-training, during (weeks 4 and 8), and post-training (week 12) in order to determine salivary SIgA and cathelicidin (indices of mucosal immunity) and α-amylase (indicator of stress). Initial (baseline) and post-training serum 25(OH)D levels were measured. Results were as follows: serum 25(OH)D levels were 37% higher in recruits entering training in summer compared with winter. A positive relationship was observed between baseline 25(OH)D levels and SIgA secretion rates (-SR). When stress levels were high during summer training, baseline 25(OH)D levels contributed to an increase in salivary secretory immunoglobulin A secretion rates (SIgA-SR) and cathelicidin-SR, the latter only in males. Vitamin D supplementation contributed to the changes in SIgA-SR and cathelicidin-SR, specifically SIgA-SR was higher in the treatment group. These data highlight the importance of vitamin D and mucosal immune responses during arduous basic military training when stress levels are increased.

Exposure to extreme hyperbaric oxygen (HBO2) >5–6 atmospheres absolute (ATA) produces baroreflex impairment, sympathetic hyperactivation, hypertension, tachycardia, and cerebral hyperemia, known as phase II, culminating in seizures. We hypothesized that attenuation of the effects of high sympathetic outflow would preserve regional cerebral blood flow (rCBF) and protect against HBO2-induced seizures. To explore this possibility, we tested four adrenoceptor antagonists in conscious and anesthetized rats exposed to HBO2at 5 and 6 ATA, respectively: phentolamine (nonselective α1and α2), prazosin (selective α1), propranolol (nonselective β1and β2), and atenolol (selective β1). In conscious rats, four drug doses were administered to rats before HBO2exposures, and seizure latencies were recorded. Drug doses that provided similar protection against seizures were administered before HBO2exposures in anesthetized rats to determine the effects of adrenoceptor blockade on mean arterial pressure, heart rate, rCBF, and EEG spikes. All four drugs modified cardiovascular and rCBF responses in HBO2that aligned with epileptiform discharges, but only phentolamine and propranolol effectively increased EEG spike latencies by ~20 and 36 min, respectively. When phentolamine and propranolol were delivered during HBO2at the onset of phase II, only propranolol led to sustained reductions in heart rate and rCBF, preventing the appearance of epileptiform discharges. The enhanced effectiveness of propranolol may extend beyond β-adrenoceptor blockade, i.e., membrane stability and reduced metabolic activity. These results indicate that adrenoceptor drug pretreatment will minimize the effects of excessive sympathetic outflow on rCBF and extend HBO2exposure time.NEW & NOTEWORTHY Blocking adrenergic receptors with phentolamine (nonselective α1and α2), prazosin (selective α1), propranolol (nonselective β1and β2), and atenolol (selective β1) modified cardiovascular and regional cerebral blood flow (rCBF) responses in hyperbaric oxygen (HBO2) at 6 atmospheres absolute (ATA); however, only phentolamine and propranolol extended EEG spike latencies. When these two agents were delivered at the onset of sympathetic hyperactivation, only propranolol reduced heart rate and rCBF throughout the exposure and prevented epileptiform discharges. These data validate the strong role of adrenergic control of cardiovascular function and rCBF in extreme HBO2and the potential use of antiadrenergic drugs to prevent seizures.

The interplay between hyper-glycemia and -lipidemia in diabetes mellitus (DM) is important in simulating diabetic conditions. However, cell culture media typically contain supraphysiological levels of glucose to stimulate cellular growth, which also desensitizes cells to elevated glucose levels. Moreover, creating hyperlipidemic conditions in vitro requires specialized carriers because unbound lipids form micelles when introduced to liquid media. This study sought to develop a novel method for simulating DM conditions in vitro.We acclimated the CAcclimated cells exposed to these hyper-glycemic (15 mM glucose) and/or -lipidemic (0.25 mM palmitate) conditions for 2 h showed increased mitochondrial fragmentation and membrane potential as well as elevated reactive oxygen species production compared to control cells. These findings suggest altered mitochondrial morphology and function, which have been confirmed using isolated rat flexor digitorum brevis myofibers. Hyper-glycemic and/or -lipidemic stimulations for 24 h significantly increased mitogen-activated protein kinase kinase MEK 1/2 protein expression, upregulated the early pro-apoptotic transcription factor C/EBP homologous protein (CHOP), and induced apoptosis.Our results further support and confirm the utility of this method which will allow for subsequent investigations studying the effects of hyper-glycemia and/or -lipidemia in vitro.

The endogenous vasodilator and signaling molecule nitric oxide has been implicated in cerebral hyperemia, sympathoexcitation, and seizures induced by hyperbaric oxygen (HBO2) at or above 3 atmospheres absolute (ATA). It is unknown whether these events in the onset of central nervous system oxygen toxicity originate within specific brain structures and whether blood flow is diverted to the brain from peripheral organs with high basal flow, such as the kidney. To explore these questions, total and regional cerebral blood flow (CBF) were measured in brain structures of the central autonomic network in anesthetized rats in HBO2at 6 ATA. Electroencephalogram (EEG) recordings, cardiovascular hemodynamics, and renal blood flow (RBF) were also monitored. As expected, mean arterial blood pressure and total and regional CBF increased preceding EEG spikes while RBF was unaltered. Of the brain structures examined, the earliest rise in CBF occurred in the striatum, suggesting increased neuronal activation. Continuous unilateral or bilateral striatal infusion of the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester attenuated CBF responses in that structure, but global EEG discharges persisted and did not differ from controls. Our novel findings indicate that: 1) cerebral hyperemia in extreme HBO2in rats does not occur at the expense of renal perfusion, highlighting the remarkable autoregulatory capability of the kidney, and 2) in spite of a sentinel increase in striatal blood flow, additional brain structure(s) likely govern the pathogenesis of HBO2-induced seizures because EEG discharge latency was unchanged by local blockade of striatal nitric oxide production and concomitant hyperemia.

Submariners spend prolonged periods submerged without sunlight exposure and may benefit from vitamin D supplementation to maintain vitamin D status. The primary objective of this study was to determine the efficacy of daily vitamin D supplementation on maintenance of 25-hydroxyvitamin D (25(OH)D) during a 3-month submarine patrol. Submariners were randomly divided into three groups: placebo (n = 16), 1,000 IU/day (n = 20), or 2,000 IU/day (n = 17). Anthropometrics, self-reported dietary calcium and vitamin D intake, serum markers of vitamin D and bone metabolism, and peripheral quantitative computed tomography (pQCT) parameters of the tibia were determined before and after the patrol. Prior to departure, 49 % of the subjects were vitamin D insufficient (

Confined space, limited exercise equipment, rotating shift work and reduced sleep may affect cardiometabolic health in submariners. To test this hypothesis, 53 male U.S. Submariners (20–39 years) were studied before and after a 3-month routine submarine patrol. Measures included anthropometrics, dietary and physical activity, biomarkers of cardiometabolic health, energy and appetite regulation, and inflammation. Before deployment, 62% of submariners had a body fat % (BF%) ≥ 25% (obesity), and of this group, 30% met the criteria for metabolic syndrome. In obese volunteers, insulin, the homeostatic model assessment of insulin resistance (HOMA-IR), leptin, the leptin/adiponectin ratio, and pro-inflammatory chemokines growth-related oncogene and macrophage-derived chemokine were significantly higher compared to non-obese submariners. Following the patrol, a significant mean reduction in body mass (5%) and fat-mass (11%) occurred in the obese group as a result of reduced energy intake (~2000 kJ) during the patrol; and, independent of group, modest improvements in serum lipids and a mean reduction in interferon γ-induced protein 10 and monocyte chemotactic protein 1 were observed. Since 43% of the submariners remained obese, and 18% continued to meet the criteria for metabolic syndrome following the patrol, the magnitude of weight loss was insufficient to completely abolish metabolic dysfunction. Submergence up to 3-months, however, does not appear to be the cause of obesity, which is similar to that of the general population.

TO THE EDITOR: The debate between Scott et al. (6) and Llanos et al. (4) highlights the remarkable ability of birds and mammals to adapt and survive at high altitudes and cope with reduced oxygen (O2) availability. Scott and colleagues (6) make a compelling argument that birds are far superior to mammals at adapting and thriving in hypoxic environments, both at rest and during exercise. While their argument is supported by comparisons between birds and terrestrial mammals, it ignores marine mammals. Marine mammals such as seals are routinely exposed to and tolerate long bouts of hypoxia during breath-hold diving. For example, elephant seals may dive to depths of nearly 1,600 m and occasionally remain submerged for 2 h (3). Moreover, marine mammals can be exposed to partial pressures of arterial oxygen (PaO2) as low as 12 mmHg during free dives (5), which is less than the 20 mmHg observed in the bar-headed goose (6). Interestingly, a PaO2 of 12 mmHg observed in elephant seals corresponds to arterial saturations and O2 content of only 8% and 2.7 ml O2/dl (5). Thus marine mammals such as the elephant seal demonstrate a remarkable hypoxia tolerance. The integration of several key physiological adaptations including 1) substantially greater myoglobin concentrations compared to other mammals, 2) reductions in metabolism, 3) a greater reliance on aerobic metabolism (i.e., less lactate production), 4) a host of dramatic acute cardiovascular adjustments; and 5) an increased intrinsic cerebral hypoxia tolerance allow marine mammals to thrive in hypoxic environments and enable long deep dives (1–3).

This study sought to elucidate the effects of a low- and high-load jump resistance exercise (RE) training protocol on cancellous bone of the proximal tibia metaphysis (PTM) and femoral neck (FN). Sprague-Dawley rats (male, 6 mo old) were randomly assigned to high-load RE (HRE; n = 16), low-load RE (LRE; n = 15), or sedentary cage control (CC; n = 11) groups. Animals in the HRE and LRE groups performed 15 sessions of jump RE during 5 wk of training. PTM cancellous volumetric bone mineral density (vBMD), assessed by in vivo peripheral quantitative computed tomography scans, significantly increased in both exercise groups (+9%; P < 0.001), resulting in part from 130% (HRE; P = 0.003) and 213% (LRE; P < 0.0001) greater bone formation (measured by standard histomorphometry) vs. CC. Additionally, mineralizing surface (%MS/BS) and mineral apposition rate were higher (50–90%) in HRE and LRE animals compared with controls. PTM bone microarchitecture was enhanced with LRE, resulting in greater trabecular thickness ( P = 0.03) and bone volume fraction (BV/TV; P = 0.04) vs. CC. Resorption surface was reduced by nearly 50% in both exercise paradigms. Increased PTM bone mass in the LRE group translated into a 161% greater elastic modulus ( P = 0.04) vs. CC. LRE and HRE increased FN vBMD (10%; P < 0.0001) and bone mineral content (∼20%; P < 0.0001) and resulted in significantly greater FN strength vs. CC. For the vast majority of variables, there was no difference in the cancellous bone response between the two exercise groups, although LRE resulted in significantly greater body mass accrual and bone formation response. These results suggest that jumping at minimal resistance provides a similar anabolic stimulus to cancellous bone as jumping at loads exceeding body mass.

Aim: The purpose of this study was to determine the anabolic response of a single bout of high intensity resistance exercise (RE) following 5 weeks of RE training. Methods: To complete these studies, Sprague–Dawley rats were assigned by body mass to RE, exercise control (EC), or sedentary cage control (CC) groups and studied over 36 h after 5 weeks of RE (squat-like) training. Cumulative (final 36 h) fractional rates of muscle protein synthesis (FSR) were determined by 2H2O, and acute (16 h post-RE) rates of muscle protein synthesis (RPS) were determined by flooding with l-[2,3,4,5,6-3H]phenylalanine. Regulators of peptide-chain initiation, 4E-BP1, eIF4E and the association of the two were determined by Western blotting and immunoprecipitation respectively. Results: No differences were observed with acute measures of RPS obtained 16 h following the final exercise bout in the plantaris or soleus muscles (P > 0.05). Consistent with this observation, 4E-BP1 was similarly phosphorylated and bound to eIF4E among all groups. However, upon determination of the cumulative response, FSR was significantly increased in the plantaris of RE vs. EC and CC (0.929 ± 0.094, 0.384 ± 0.039, 0.300 ± 0.022% h−1 respectively; P

A comprehensive understanding of animal growth requires adequate knowledge of protein synthesis (PS), which in fish, has traditionally been determined by the flooding dose method. However, this procedure is limited to short-term assessments and may not accurately describe fish growth over extended periods of time. Since deuterium oxide ((2)H(2)O) has been used to non-invasively quantify PS in mammals over short- and long-term periods, we aimed at determining if (2)H(2)O could also be used to measure PS in channel catfish. Fish were stocked in a 40-L aquarium with approximately 4% (2)H(2)O and sampled at 4, 8 and 24h (n=6 at each time period) to determine (2)H-labeling of body water (plasma), as well as protein-free and protein-bound (2)H-labeled alanine. The labeling of body water reflected that of aquarium water and the labeling of protein-free alanine remained constant over 24h and was approximately 3.8 times greater than that of body water. By measuring (2)H-labeled alanine incorporation after 24h of (2)H(2)O exposure we were able to calculate a rate of PS: 0.04+/-0.01% h(-1). These results demonstrate that PS in fish can be effectively measured using (2)H(2)O and, because this method yields integrative measures of PS, is relatively inexpensive and accounts for perturbations such as feeding, it is a novel and practical assessment option.

A hookah smoker who was treated for severe carbon monoxide poisoning with hyperbaric oxygen reported using a different type of charcoal prior to hospital admission, i.e., quick-light charcoal. This finding led to a study aimed at determining whether CO production differs between charcoals commonly used for hookah smoking, natural and quick-light. Our hypothesis was that quick-light charcoal produces significantly more CO than natural charcoal. A medium-sized hookah, activated charcoal filter, calibrated syringe, CO gas analyzer and infrared thermometer were assembled in series. A single 9-10 g briquette of either natural or quick-light charcoal was placed atop the hookah bowl and ignited. CO output (ppm) and temperature (degrees C) were measured in three-minute intervals over 90 minutes. The mean CO levels produced by quick-light charcoal over 90 minutes was significantly higher (3728 ± 2028) compared to natural charcoal (1730 ± 501 ppm, p = 0.016). However, the temperature was significantly greater when burning natural charcoal (292 ± 87) compared to quick-light charcoal (247 ± 92 degrees C, p = 0.013). The high levels of CO produced when using quick-light charcoals may be contributing to the increase in reported hospital admissions for severe CO poisoning.

An imbalance between glutamatergic and g-aminobutyric acid (GABA)ergic synaptic transmission is associated with hyperbaric oxygen (HBO2) induced seizures. Here we explored the impact of S-nitrosyla...

Background While awaiting rescue from a disabled submarine, survivors will likely endure an atmosphere of rising CO2 that will result in CO2 toxicity once the available emergency CO2 scrubbing materials are exhausted. Propranolol is a beta-blocker that may increase survival time by reducing metabolic CO2 production (VCO2). The purpose of this study was to determine if propranolol reduces resting VCO2 in healthy men. Methods Eight healthy men completed a counterbalanced, randomized, placebo-controlled, double-blinded crossover study in which each subject received propranolol (40 mg twice daily) or placebo (lactose pill twice daily) over 72 h. The alternate condition was separated by a minimum 96-h washout period. Resting VCO2, oxygen consumption (VO2), ventilation (VE), respiration rate (RR), respiratory exchange ratio (RER), mean arterial pressure (MAP), heart rate (HR), and cardiac output (Q) were measured each morning and afternoon. Results When compared to placebo, propranolol significantly reduced VCO2 (-6.5%), MAP (-3.6%), HR (-10.4%), and Q (-8.2%); however, there were no significant differences in VO2, RR, VE, or RER. Discussion These results show that 40 mg of propranolol taken twice daily reduces resting VCO2 in healthy men and suggests that this treatment strategy may increase survival time in a disabled submarine scenario.

Metabolic risk factors associated with insulin resistance syndrome may attenuate augmentations in skeletal muscle protein anabolism following contractile activity. The purpose of this study was to investigate whether or not the anabolic response, as defined by an increase in cumulative fractional protein synthesis rates (24-h FSR) following resistance exercise (RE), is blunted in skeletal muscle of a well-established rodent model of insulin resistance syndrome. Four-month-old lean ( Fa/?) and obese ( fa/fa) Zucker rats engaged in four lower body RE sessions over 8 days, with the last bout occurring 16 h prior to muscle harvest. A priming dose of deuterium oxide (2H2O) and 2H2O-enriched drinking water were administered 24 h prior to euthanization for assessment of cumulative FSR. Fractional synthesis rates of mixed (−5%), mitochondrial (−1%), and cytosolic (+15%), but not myofibrillar, proteins (−16%, P = 0.012) were normal or elevated in gastrocnemius muscle of unexercised obese rats. No statistical differences were found in the anabolic response of cytosolic and myofibrillar subfractions between phenotypes, but obese rats were not able to augment 24-h FSR of mitochondria to the same extent as lean rats following RE (+14% vs. +28%, respectively). We conclude that the mature obese Zucker rat exhibits a mild, myofibrillar-specific suppression in basal FSR and a blunted mitochondrial response to contractile activity in mixed gastrocnemius muscle. These findings underscore the importance of assessing synthesis rates of specific myocellular subfractions to fully elucidate perturbations in basal protein turnover rates and differential adaptations to exercise stimuli in metabolic disease.

The primary objective of this investigation was to determine whether 2H2O and phenylalanine (Phe) flooding dose methods yield comparable fractional rates of protein synthesis (FSR) in skeletal muscle following a single bout of high-intensity resistance exercise (RE). Sprague-Dawley rats were assigned by body mass to either 4-h control (CON 4 h; n = 6), 4-h resistance exercise (RE 4 h; n = 6), 24-h control (CON 24 h; n = 6), or 24-h resistance exercise (RE 24 h; n = 6). The RE groups were operantly conditioned to engage in a single bout of high-intensity, “squat-like” RE. All rats were given an intraperitoneal injection of 99.9% 2H2O and provided 4.0% 2H2O drinking water for either 24 ( n = 12) or 4 h ( n = 12) prior to receiving a flooding dose of l-[2,3,4,5,6-3H]Phe 16 h post-RE. Neither method detected an effect of RE on FSR in the mixed gastrocnemius, plantaris, or soleus muscle. Aside from the qualitative similarities between methods, the 4-h 2H2O FSR measurements, when expressed in percent per hour, were quantitatively greater than the 24-h 2H2O and Phe flooding in all muscles ( P < 0.001), and the 24-h 2H2O was greater than the Phe flooding dose in the mixed gastrocnemius and plantaris ( P < 0.05). In contrast, the actual percentage of newly synthesized protein was significantly higher in the 24- vs. 4-h 2H2O and Phe flooding dose groups ( P < 0.001). These results suggest that the methodologies provide “qualitatively” similar results when a perturbation such as RE is studied. However, due to potential quantitative differences between methods, the experimental question should determine what approach should be used.

Background:We recently reported a strong positive association of dietary cholesterol and skeletal muscle responses to resistance training (Riechman, 2007). To confirm these findings we conducted a ...

Skeletal muscle protein synthesis has generally been determined by the precursor:product labeling approach using labeled amino acids (e.g., [13C]leucine or [13C]-, [15N]-, or [2H]phenylalanine) as the tracers. Although reliable for determining rates of protein synthesis, this methodological approach requires experiments to be conducted in a controlled environment, and as a result, has limited our understanding of muscle protein renewal under free-living conditions over extended periods of time (i.e., integrative/cumulative assessments). An alternative tracer, 2H2O, has been successfully used to measure rates of muscle protein synthesis in mice, rats, fish and humans. Moreover, perturbations such as feeding and exercise have been included in these measurements without exclusion of common environmental and biological factors. In this review, we discuss the principle behind using 2H2O to measure muscle protein synthesis and highlight recent investigations that have examined the effects of feeding and exercise. The framework provided in this review should assist muscle biologists in designing experiments that advance our understanding of conditions in which anabolism is altered (e.g., exercise, feeding, growth, debilitating and metabolic pathologies).