bluuebunny/crossref_metadata_2025 huggingface dataset:
Capillary filtration coefficient, vascular resistance, and compliance in isolated mouse lungs
Authors: Parker James C. , Gillespie Mark N. , Taylor Aubrey E. , Martin Sherri L.
Published: December 2017

Although many recently produced transgenic mice possess gene alterations affecting pulmonary vascular function, there are few baseline measurements of vascular resistance and permeability. Therefore, we excised the lungs of C57/BL6 mice and perfused them with 5% bovine serum albumin in RPMI-1640 culture medium at a nominal flow of 0.5 ml/min and ventilated them with 20% O2-5% CO2-75% N2. The capillary filtration coefficient, a sensitive measurement of hydraulic conductivity, was unchanged over 2 h (0.33 ± 0.03 ml ⋅ min−1 ⋅ cmH2O−1 ⋅ 100 g−1) in a control group ventilated with low peak inflation pressures (PIP) but increased 4.3-fold after high PIP injury. Baseline pulmonary vascular resistance was 6.1 ± 0.4 cmH2O ⋅ ml−1 ⋅ min ⋅ 100 g−1 and was distributed 34% in large arteries, 18% in small arteries, 14% in small veins, and 34% in large veins on the basis of vascular occlusion pressures. Baseline vascular compliance was 5.4 ± 0.3 ml ⋅ cmH2O−1 ⋅ 100 g−1 and decreased significantly with increased vascular pressures. Baseline pulmonary vascular resistance was inversely related to both perfusate flow and microvascular pressure and increased to 202% of baseline after infusion of 10−4 M phenylephrine due to constriction of large arterial and venous segments. Thus isolated mouse lung vascular permeability, vascular resistance, and the longitudinal distribution of vascular resistance are similar to those in other species and respond in a predictable manner to microvascular injury and a vasoconstrictor agent.
Systemic hypoxia promotes leukocyte-endothelial adherence via reactive oxidant generation
Authors: Wood John G. , Johnson Jennifer S. , Mattioli Leone F. , Gonzalez Norberto C.
Published: December 2017

We recently demonstrated that systemic hypoxia during reduced inspired [Formula: see text] produces a rapid increase in leukocyte adherence to rat mesenteric venules. Evidence suggests that the mechanism of this response involves decreased nitric oxide (NO) levels. One possible pathway for NO depletion could involve increased reactive oxygen species (ROS) generation resulting in inactivation of NO. The overall goal of the present study was to examine the role of ROS in promoting leukocyte-endothelial adherence during systemic hypoxia. Experiments were designed to 1) evaluate changes in ROS generation in the mesenteric microcirculation during systemic hypoxia, 2) determine how the ROS signal changes when [Formula: see text] levels return to normal after a period of systemic hypoxia, 3) assess the effect of antioxidants on ROS generation during hypoxia, and 4) utilize antioxidants to examine the functional relationship between ROS generation and leukocyte adherence during hypoxia. The major findings from this study are that systemic hypoxia increases ROS generation within the mesenteric microcirculation and that antioxidants prevent the increase in leukocyte-endothelial adhesive interactions observed in hypoxia.
Catchlike-inducing train activation of human muscle during isotonic contractions: burst modulation
Authors: Lee Samuel C. K. , Becker Cara N. , Binder-Macleod Stuart A.
Published: December 2017

Stimulation trains that exploit the catchlike property [catchlike-inducing trains (CITs)] produce greater forces and rates of rise of force than do constant-frequency trains (CFTs) during isometric contractions and isovelocity movements. This study examined the effect of CITs during isotonic contractions in healthy subjects. Knee extension was electrically elicited against a load of 10% of maximum voluntary isometric contraction. The stimulation intensity was set to produce 20% of maximum voluntary isometric contraction. The muscle was tested before and after fatigue with a 6-pulse CFT and 6-pulse CITs that contained an initial doublet, triplet, or quadruplet. For prefatigue responses, the greatest isotonic performance was produced by CITs with initial doublets. When the muscles were fatigued, triplet CITs were best. CITs produce greater excursion, work, peak power, and average power than do CFTs, because CITs produced more rapid rates of rise of force. Faster rates of rise of force enabled the preload on the muscle to be exceeded earlier during the stimulation train.
Density dependence of forced expiratory flows in healthy infants and toddlers
Authors: Davis Stephanie , Jones Marcus , Kisling Jeff , Castile Robert , Tepper Robert S.
Published: December 2017

In older children and adults, density dependence (DD) of forced expiratory flow is present over the majority of the full flow-volume curve. In healthy subjects, DD occurs because the pressure drop from peripheral to central airways is primarily dependent on turbulence and convective acceleration rather than laminar resistance; however, an increase in peripheral resistance reduces DD. We measured DD of forced expiratory flow in 22 healthy infants to evaluate whether infants have low DD. Full forced expiratory maneuvers were obtained while the subjects breathed room air and then a mixture of 80% helium-20% oxygen. Flows at 50 and 75% of expired forced vital capacity (FVC) were measured, and the ratio of helium-oxygen to air flow was calculated (DD at 50 and 75% FVC). The mean (range) of DD at 50 and 75% FVC was 1.37 (1.22–1.54) and 1.23 (1.02–1.65), respectively, values similar to those reported in older children and adults. There were no significant relationships between DD and age. Our results suggest that infants, compared with older children and adults, have similar DD, a finding that suggests that infants do not have a greater ratio of peripheral-to-central airway resistance.
Stiffness-distortion sarcomere model for muscle simulation
Authors: Razumova Maria V. , Bukatina Anna E. , Campbell Kenneth B.
Published: December 2017

A relatively simple method is presented for incorporating cross-bridge mechanisms into a muscle model. The method is based on representing force in a half sarcomere as the product of the stiffness of all parallel cross bridges and their average distortion. Differential equations for sarcomeric stiffness are derived from a three-state kinetic scheme for the cross-bridge cycle. Differential equations for average distortion are derived from a distortional balance that accounts for distortion entering and leaving due to cross-bridge cycling and for distortion imposed by shearing motion between thick and thin filaments. The distortion equations are unique and enable sarcomere mechanodynamics to be described by only a few ordinary differential equations. Model predictions of small-amplitude step and sinusoidal responses agreed well with previously described experimental results and allowed unique interpretations to be made of various response components. Similarly good results were obtained for model reproductions of force-velocity and large-amplitude step and ramp responses. The model allowed reasonable predictions of contractile behavior by taking into account what is understood to be basic muscle contractile mechanisms.
Exercise-induced arterial hypoxemia
Authors: Dempsey Jerome A. , Wagner Peter D.
Published: December 2017

Exercise-induced arterial hypoxemia (EIAH) at or near sea level is now recognized to occur in a significant number of fit, healthy subjects of both genders and of varying ages. Our review aims to define EIAH and to critically analyze what we currently understand, and do not understand, about its underlying mechanisms and its consequences to exercise performance. Based on the effects on maximal O2uptake of preventing EIAH, we suggest that mild EIAH be defined as an arterial O2saturation of 93–95% (or 3–4% <rest), moderate EIAH as 88–93%, and severe EIAH as <88%. Both an excessive alveolar-to-arterial[Formula: see text] difference (a-a Do2) (>25–30 Torr) and inadequate compensatory hyperventilation (arterial [Formula: see text] >35 Torr) commonly contribute to EIAH, as do acid- and temperature-induced shifts in O2dissociation at any given arterial [Formula: see text]. In turn, expiratory flow limitation presents a significant mechanical constraint to exercise hyperpnea, whereas ventilation-perfusion ratio maldistribution and diffusion limitation contribute about equally to the excessivea-a Do2. Exactly how diffusion limitation is incurred or how ventilation-perfusion ratio becomes maldistributed with heavy exercise remains unknown and controversial. Hypotheses linked to extravascular lung water accumulation or inflammatory changes in the “silent” zone of the lung's peripheral airways are in the early stages of exploration. Indirect evidence suggests that an inadequate hyperventilatory response is attributable to feedback inhibition triggered by mechanical constraints and/or reduced sensitivity to existing stimuli; but these mechanisms cannot be verified without a sensitive measure of central neural respiratory motor output. Finally, EIAH has detrimental effects on maximal O2uptake, but we have not yet determined the cause or even precisely identified which organ system, involved directly or indirectly with O2transport to muscle, is responsible for this limitation.
Diversity in levels of intracellular total creatine and triglycerides in human skeletal muscles observed by1H-MRS
Authors: Rico-Sanz Jesús , Thomas E. Louise , Jenkinson Gabriele , Mierisová Šárka , Iles Richard , Bell Jimmy D.
Published: December 2017

We used1H-magnetic resonance spectroscopy to noninvasively determine total creatine (TCr), choline-containing compounds (Cho), and intracellular (IT) and extracellular (between-muscle fibers) triglycerides (ET) in three human skeletal muscles. Subjects' ( n = 15 men) TCr concentrations in soleus [Sol; 100.2 ± 8.3 (SE) mmol/kg dry wt] were lower ( P < 0.05) than those in gastrocnemius (Gast; 125.3 ± 9.2 mmol/kg dry wt) and tibialis anterior (TA; 123.7 ± 8.8 mmol/kg dry wt). The Cho levels in Sol (35.8 ± 3.6 mmol/kg dry wt) and Gast (28.5 ± 3.5 mmol/kg dry wt) were higher ( P < 0.001 and P < 0.01, respectively) compared with TA (13.6 ± 2.4 mmol/kg dry wt). The IT values were found to be 44.8 ± 4.6 and 36.5 ± 4.2 mmol/kg dry wt in Sol and Gast, respectively. The IT values of TA (24.5 ± 4.5 mmol/kg dry wt) were lower than those of Sol ( P < 0.01) and Gast ( P < 0.05). There were no differences in ET [116.0 ± 11.2 (Sol), 119.1 ± 18.5 (Gast), and 91.4 ± 19.2 mmol/kg dry wt (TA)]. It is proposed that the differences in metabolite levels may be due to the differences in fiber-type composition and deposition of metabolites due to the adaptation of different muscles during locomotion.
Extracellular calcium modulates generation of reactive oxygen species by the contracting diaphragm
Authors: Supinski G. , Nethery D. , Stofan D. , DiMarco A.
Published: December 2017

Recent studies have indicated that free radicals may play an important role in the development of muscle dysfunction in many pathophysiological conditions. Because the degree of muscle dysfunction observed in some of these conditions appears to be both free radical dependent and modulated by extracellular calcium concentrations, we thought that there may be a link between these two phenomena; i.e., the propensity of a muscle to generate free radicals may be dependent on extracellular calcium concentrations. For this reason, we compared formation of reactive oxygen species (ROS; i.e., free radicals) by electrically stimulated rat diaphragms (trains of 20-Hz stimuli for 10 min, train rate 0.25 trains/s) incubated in organ baths filled with physiological solutions containing low (1 mM), normal (2.5 mM), or high (5 mM) calcium levels. Generation of ROS was assessed by measuring the conversion of hydroethidine to ethidium. We found ROS generation with contraction varied with the extracellular calcium level, with low ROS production (3.18 ± 0.40 ng ethidium/mg tissue) for low-calcium studies and with much higher ROS generation for normal-calcium (18.90 ± 2.70 ng/mg) or high-calcium (19.30 ± 4.50 ng/mg) studies ( P < 0.001). Control, noncontracting diaphragms (in 2.5 mM calcium) had little ROS production (3.40 ± 0.80 ng/mg; P < 0.001). To further investigate this issue, we added nimodipine (20 μM), an L-type calcium channel blocker, to contracting diaphragms (2.5 mM calcium bath) and found that nimodipine also suppressed ROS formation (2.56 ± 0.85 ng ethidium/mg tissue). These data indicate that ROS generation by the contracting diaphragm is strongly influenced by extracellular calcium concentrations and may be dependent on calcium transport through L-type calcium channels.
Influence of mild exercise at the lactate threshold on glucose effectiveness
Authors: Sakamoto Makoto , Higaki Yasuki , Nishida Yuichiro , Kiyonaga Akira , Shindo Munehiro , Tokuyama Kumpei , Tanaka Hiroaki
Published: December 2017

The effect of a single bout of mild exercise on glucose effectiveness (SG) and insulin sensitivity (SI) was studied in six young male subjects by using a minimal model. An intravenous glucose tolerance test was performed under two conditions as follows: 1) 25 min after a bout of exercise on a cycle ergometer at the lactate threshold level for 60 min (Ex) and 2) without any prior exercise (Con). Leg blood flow (LBF) was also measured by strain-gauge plethysmography simultaneously with blood sampling. SI did not significantly change after exercise (18.1 ± 1.5 vs. 17.7 ± 1.9 × 10−5 min/pM), whereas SG significantly increased (0.016 ± 0.002 vs. 0.025 ± 0.002 min−1, P < 0.01). The increased blood flow after exercise remained high during the time period for measurement of the glucose disappearance constant and may be a determinant of SG. The incremental lactate area under the curve until insulin loading was also significantly higher in Ex than in Con (2.6 ± 0.9 vs. −3.5 ± 1.5 mM/min, P < 0.05). These results suggest that increased SG after mild exercise may be due, at least in part, to increased LBF and lactate production under a hyperglycemic state.
Role of neutrophils in xanthine/xanthine oxidase-induced oxidant injury in isolated rabbit lungs
Authors: Kishi Masashi , Richard Lois F. , Webster Robert O. , Dahms Thomas E.
Published: December 2017

Reactive oxygen species have been shown to play an important role in the pathogenesis of lung injury. This study was designed to clarify the role of intrapulmonary neutrophils in the development of xanthine/xanthine oxidase (X/XO)-induced lung injury in isolated buffer-perfused rabbit lungs. We measured microvascular fluid filtration coefficient ( K f) and wet-to-dry weight ratio to assess lung injury. X/XO induced a significant increase in K f and wet-to-dry weight ratio in neutrophil-replete lungs, whereas the lung injury was attenuated in neutrophil-depleted lungs. A neutrophil elastase inhibitor, ONO-5046, also attenuated the lung injury. In addition, X/XO induced a transient pulmonary arterial pressure (Ppa) increase. The thromboxane inhibitor OKY-046 attenuated the Ppa increase but did not alter the increase in permeability. Neutrophil depletion reduced the K f increase but had no effect on the Ppa increase. These results suggest that intrapulmonary neutrophils activated by X/XO play a major role in development of the lung injury, that neutrophil elastase is involved in the injury, and that the X/XO-induced vasoconstriction is independent of intrapulmonary neutrophils.
Effects of genetic selection and voluntary activity on the medial gastrocnemius muscle in house mice
Authors: Zhan Wen-Zhi , Swallow John G. , Garland Theodore , Proctor David N. , Carter Patrick A. , Sieck Gary C.
Published: December 2017

In a previous study (J. G. Swallow, T. Garland, Jr., P. A. Carter, W.-Z. Zhan, and G. C. Sieck, J. Appl. Physiol.84: 69–76, 1998), we found that in house mice both genetic selection (10 generations of artificial selection for high voluntary activity on running wheels) and access to running wheels (7–8 weeks) elicited a modest increase in maximal oxygen consumption. Based on these results, we hypothesized that genetic selection would affect the changes in endurance and oxidative capacity of the medial gastrocnemius (MG) muscle induced by wheel access (training response). Wheel access increased the isotonic endurance of the MG in both genetically selected and random-bred (control) mice. However, this exercise-induced improvement in isotonic endurance of the MG was similar between genetically selected and control mice. Wheel access also increased the succinate dehydrogenase activity of MG muscle fibers in both selected and control lines. However, this exercise-induced increase in succinate dehydrogenase activity was comparable between genetically selected and control animals. Taken together, these results indicate that the modest increase in maximal oxygen consumption associated with genetic selection is not reflected by the training-induced changes in oxidative capacity and endurance of MG muscle fibers.
A method of endotracheal intubation and pulmonary functional assessment for repeated studies in mice
Authors: Brown Robert H. , Walters Dianne M. , Greenberg Robert S. , Mitzner Wayne
Published: December 2017

The ability to successfully intubate the trachea of mice and control their ventilation is important for longitudinal studies requiring recovery from anesthesia and repeated pulmonary function measurements or other evaluations, such as the use of radiological imaging (e.g., computed tomography or magnetic resonance imaging). We describe a method for rapid and repeated intubation of mice, with subsequent pulmonary function measurements at baseline and after an agonist challenge. We describe a simply constructed metal blade used as a laryngoscope to facilitate oropharyngeal exposure, transillumination of the neck to facilitate visualization of the trachea through the oropharynx, readily available polyethylene tubing to intubate the trachea, and a simple solenoid ventilator to maintain physiological ventilation and assess respiratory resistance and compliance. Brief infusions of acetylcholine through a needle into the jugular vein are used to assess the responsiveness of the airway smooth muscle.
Severe diabetes prohibits elevations in muscle protein synthesis after acute resistance exercise in rats
Authors: Fedele Mark J. , Hernandez Jazmir M. , Lang Charles H. , Vary Thomas C. , Kimball Scot R. , Jefferson Leonard S. , Farrell Peter A.
Published: December 2017

This study determined whether rates of protein synthesis increase after acute resistance exercise in skeletal muscle from severely diabetic rats. Previous studies consistently show that postexercise rates of protein synthesis are elevated in nondiabetic and moderately diabetic rats. Severely diabetic rats performed acute resistance exercise ( n= 8) or remained sedentary ( n = 8). A group of nondiabetic age-matched rats served as controls ( n = 9). Rates of protein synthesis were measured 16 h after exercise. Plasma glucose concentrations were >500 mg/dl in the diabetic rats. Rates of protein synthesis (nmol phenylalanine incorporated ⋅ g muscle−1⋅ h−1, means ± SE) were not different between exercised (117 ± 7) and sedentary (106 ± 9) diabetic rats but were significantly ( P < 0.05) lower than in sedentary nondiabetic rats (162 ± 9) and in exercised nondiabetic rats (197 ± 7). Circulating insulin concentrations were 442 ± 65 pM in nondiabetic rats and 53 ± 11 and 72 ± 19 pM in sedentary and exercised diabetic rats, respectively. Plasma insulin-like growth factor I concentrations were reduced by 33% in diabetic rats compared with nondiabetic rats, and there was no difference between exercised and sedentary diabetic rats. Muscle insulin-like growth factor I was not affected by resistance exercise in diabetic rats. The results show that there is a critical concentration of insulin below which rates of protein synthesis begin to decline in vivo. In contrast to previous studies using less diabetic rats, severely diabetic rats cannot increase rates of protein synthesis after acute resistance exercise.
Effect of creatine loading on neuromuscular fatigue threshold
Authors: Stout Jeffrey , Eckerson Joan , Ebersole Kyle , Moore Geri , Perry Sharon , Housh Terry , Bull Anthony , Cramer Joel , Batheja Ash
Published: December 2017

The purpose of this investigation was to determine the effect of creatine (Cr) loading on the onset of neuromuscular fatigue by monitoring electromyographic fatigue curves from the vastus lateralis muscle using the physical working capacity at the fatigue threshold (PWCFT) test. Using a double-blind random design, 15 women athletes [mean age 19.0 ± 2.0 (SD) yr] from the university crew team received a placebo ( n = 8; 20 g glucose) or Cr ( n = 7; 5 g Cr monohydrate + 20 g glucose) four times per day for 5 consecutive days. Analysis of covariance was used to analyze the data (covaried for presupplementation PWCFT values). The adjusted mean postsupplementation PWCFT value for the Cr group (mean = 186 W) was significantly ( P < 0.05) higher than that of the placebo group (mean = 155 W). These findings suggest that Cr loading may delay the onset of neuromuscular fatigue.
Effect of acute postexercise ethanol intoxication on the neuroendocrine response to resistance exercise
Authors: Koziris L. Perry , Kraemer William J. , Gordon Scott E. , Incledon Thomas , Knuttgen Howard G.
Published: December 2017

This investigation was conducted to determine the effect of postexercise ethanol intoxication (21.97 ± 1.09 mmol/l blood) on the response of selected aspects of the neuroendocrine system to a resistance exercise (Ex) session. Nine resistance-trained men (25.0 ± 1.4 yr, 179.4 ± 3.4 cm, 79.7 ± 3.3 kg) were used to compare three 3-day treatments: control, Ex, and ethanol after exercise (ExEt). Blood was collected serially from an antecubital vein before exercise, immediately after exercise, and for pooled analysis at 20–40 (2 samples), 60–120 (4 samples), and 140–300 (9 samples) min after exercise on day 1 and in the morning (2 samples each) on days 2 and 3. Ethanol did not increase circulating epinephrine, norepinephrine, or cortisol concentration (Cort) above Ex elevations. At 60–120 min, only ExEt Cort was greater than control Cort. Concentrations of testosterone, luteinizing hormone, and corticotropin were not affected by either treatment. It is concluded that, although this blood ethanol concentration is insufficient to acutely increase Cort above that caused by Ex alone, it appears that ethanol may have a prolonged effect beyond the Ex response. This blood ethanol concentration does not further stimulate the sympathoadrenal system during the postexercise response.
Preexercise medium-chain triglyceride ingestion does not alter muscle glycogen use during exercise
Authors: Horowitz Jeffrey F. , Mora-Rodriguez Ricardo , Byerley Lauri O. , Coyle Edward F.
Published: December 2017

This investigation determined whether ingestion of a tolerable amount of medium-chain triglycerides (MCT; ∼25 g) reduces the rate of muscle glycogen use during high-intensity exercise. On two occasions, seven well-trained men cycled for 30 min at 84% maximal O2uptake. Exactly 1 h before exercise, they ingested either 1) carbohydrate (CHO; 0.72 g sucrose/kg) or 2) MCT+CHO [0.36 g tricaprin (C10:0)/kg plus 0.72 g sucrose/kg]. The change in glycogen concentration was measured in biopsies taken from the vastus lateralis before and after exercise. Additionally, glycogen oxidation was calculated as the difference between total carbohydrate oxidation and the rate of glucose disappearance from plasma (Rdglucose), as measured by stable isotope dilution techniques. The change in muscle glycogen concentration was not different during MCT+CHO and CHO (42.0 ± 4.6 vs. 38.8 ± 4.0 μmol glucosyl units/g wet wt). Furthermore, calculated glycogen oxidation was also similar (331 ± 18 vs. 329 ± 15 μmol ⋅ kg−1⋅ min−1). The coingestion of MCT+CHO did increase ( P < 0.05) Rdglucose at rest compared with CHO (26.9 ± 1.5 vs. 20.7 ± 0.7 μmol ⋅kg−1⋅ min−1), yet during exercise Rdglucose was not different during the two trials. Therefore, the addition of a small amount of MCT to a preexercise CHO meal did not reduce muscle glycogen oxidation during high-intensity exercise, but it did increase glucose uptake at rest.
Research in the exercise sciences: Where do we go from here?
Authors: Baldwin Kenneth M.
Published: December 2017

The goal of this article is to provide a perspective on how research involving the acute and chronic effects of exercise (referred to as “exercise sciences”) on the structure and function of organs systems will evolve in the next century. Within the last 30 years, exercise-related research has rapidly transitioned from an organ to a subcellular/molecular focus. Thus future research will continue to be heavily influenced by molecular biology tools, fueled by both emerging technologies (e.g., “gene-chip microarrays”) designed to dissect gene function on a macro scale as well as by the completion of the human genome project in which the ∼80,000 genes comprising humans will be completely sequenced. These successes will drive the emerging fields of functional genomics (the dissecting of a gene's identity and function) and proteomics (the study of the properties of proteins). Funding levels at the National Institutes of Health will likely increase in order to expand these emerging fields as well as provide avenues for translating fundamental knowledge into solving the complexities of a number of degenerative diseases influenced heavily by activity/inactivity factors such as cardiopulmonary disease, diabetes, obesity, and the debilitating disorders associated with aging. Thus there are many challenges facing future exercise scientists who must harness the new technologies and take an aggressive stance in bringing this important field to the forefront.
Gender differences in glucoregulatory responses to intense exercise
Authors: Marliss Errol B. , Kreisman Stuart H. , Manzon Anthony , Halter Jeffrey B. , Vranic Mladen , Nessim Sharon J.
Published: December 2017

We compared glucoregulatory responses to intense exercise (14 min at 88% maximum O2 uptake) between genders (16 men, 12 women). Analysis of covariance of maximum O2 uptake showed no gender effect, with 82% of variance due to fat-free mass (FFM). Glycemia rose comparably during exercise but was higher in women during recovery ( P = 0.02). Glucose production [rate of appearance (Ra); in mg/min] increased markedly in both; stepwise multiple regression and analysis of covariance of Ra (peak and incremental area under the curve) showed no effect of gender, body weight, or FFM. Glucose uptake [rate of disappearance (Rd)] increased less than Ra and slower in women. Rdarea under the curve related to FFM ( P = 0.01) but not gender or body weight. Norepinephrine and epinephrine responses (13–18× baseline) were the same and correlated significantly with Ra. Exercise insulin and glucagon changes were slight, but postexercise hyperinsulinemia was greater in women ( P = 0.018), along with higher Rd. Therefore, intense exercise glucoregulation is qualitatively similar between genders, with a “feed-forward” regulation of Ra (consistent with catecholamine mediation). However, women have a lesser Rdresponse, related to FFM. This combination leads to greater recovery-period hyperglycemia and hyperinsulinemia.
Myosin heavy chain composition of skeletal muscles in young rats growing under hypobaric hypoxia conditions
Authors: Bigard A. X. , Sanchez H. , Birot O. , Serrurier B.
Published: December 2017

This study investigated the effects of voluntary wheel running on the myosin heavy chain (MHC) composition of the soleus (Sol) and plantaris muscles (Pla) in rats developing under hypobaric choronic hypoxia (CH) conditions during 4 wk in comparison with those of control rats maintained under local barometric pressure conditions (C) or rats pair-fed an equivalent quantity of food to that consumed by CH animals (PF). Compared with C animals, sedentary rats subjected to CH conditions showed a significant decrease in type I MHC in Sol (−12%, P < 0.01). Although strongly decreased under hypoxia, spontaneous running activity increased the expression of type I MHC ( P < 0.01) so that no difference in the MHC profile of Sol was shown between CH active and C active rats. The MHC distribution in Sol of PF rats was not significantly different from that found in C animals. CH resulted in a significant decrease in type I ( P < 0.01) and type IIA ( P < 0.005) MHC, concomitant with an increase in type IIB MHC in Pla ( P < 0.001), compared with C and PF animals. In contrast to results in Sol muscle, this slow-to-fast shift in the MHC profile was unaffected by spontaneous running activity. These results suggest that running exercise suppresses the hypoxia-induced slow-to-fast transition in the MHC expression in Sol muscles only. The hypoxia-induced decrease in food intake has no major influence on MHC expression in developing rats.
An investigation of pulmonary surfactant physicochemical behavior under airway reopening conditions
Authors: Ghadiali Samir N. , Gaver Donald P.
Published: December 2017

Airway reopening mechanics depend on surfactant physicochemical properties. During reopening, the progression of a finger of air down an airway creates an interface that is continually expanding into the bulk fluid. Conventional surfactometers are not capable of evaluating physicochemical behavior under these conditions. To study these aspects, we investigated the pressure required to push a semi-infinite bubble of air down a fluid-filled cylindrical capillary of radius R. The ionic surfactant SDS and pulmonary surfactant analogsl-α-dipalmitoylphosphatidylcholine and Infasurf were investigated. We found that the nonequilibrium adsorption of surfactant can create a large nonequilibrium normal stress and a surface shear stress (Marangoni stress) that increase the bubble pressure. The nonphysiological surfactant SDS is capable of eliminating the normal stress and partially reducing the Marangoni stress. The main component of pulmonary surfactant,l-α-dipalmitoylphosphatidylcholine, is not capable of reducing either stress, demonstrating slow adsorption properties. The clinically relevant surfactant Infasurf is shown to have intermediate adsorption properties, such that the nonequilibrium normal stress is reduced but the Marangoni stress remains large. Infasurf's behavior suggests that an optimal surfactant solution will have sorption properties that are fast enough to reduce the reopening pressure that may damage airway wall epithelial cells but slow enough to maintain the Marangoni stress that enhances airway stability.
Apoptosis in microvascular endothelial cells of perfused rabbit lungs with acute hydrostatic edema
Authors: Gotoh Naoki , Kambara Kenjiro , Jiang Xiao-Wen , Ohno Michiya , Emura Shoichi , Fujiwara Takako , Fujiwara Hisayoshi
Published: December 2017

We test the hypothesis that microvascular endothelial cells may undergo apoptosis in response to acute pulmonary venous hypertension. The isolated rabbit lungs were perfused in situ for 4 h with left atrial pressure of 0, 10, or 20 mmHg at a constant blood flow. Edema formation was monitored by lung weight gain. To assay for apoptosis, we performed agarose gel electrophoresis of DNA, in situ nick end labeling of DNA strand breaks, and electron microscopy. We also examined the levels of expression of Bcl-2, a suppressor of apoptosis, in microvascular endothelial cells using an immunohistochemical technique. In a vascular pressure-dependent fashion, we found apoptosis in endothelial cells of alveolar septal capillaries, as well as expression of Bcl-2 in arteriolar and venular endothelial cells. We conclude that acute pulmonary venous hypertension induces apoptosis in capillary endothelial cells but not in arteriolar and venular endothelial cells, suggesting that microvascular endothelial cell apoptosis is dependent on the levels of Bcl-2 expression and influences the formation or resolution of acute hydrostatic lung edema.
Decreased thin filament density and length in human atrophic soleus muscle fibers after spaceflight
Authors: Riley Danny A. , Bain James L. W. , Thompson Joyce L. , Fitts Robert H. , Widrick Jeffrey J. , Trappe Scott W. , Trappe Todd A. , Costill David L.
Published: December 2017

Soleus muscle fibers were examined electron microscopically from pre- and postflight biopsies of four astronauts orbited for 17 days during the Life and Microgravity Sciences Spacelab Mission (June 1996). Myofilament density and spacing were normalized to a 2.4-μm sarcomere length. Thick filament density (∼1,062 filaments/μm2) and spacing (∼32.5 nm) were unchanged by spaceflight. Preflight thin filament density (2,976/μm2) decreased significantly ( P < 0.01) to 2,215/μm2 in the overlap A band region as a result of a 17% filament loss and a 9% increase in short filaments. Normal fibers had 13% short thin filaments. The 26% decrease in thin filaments is consistent with preliminary findings of a 14% increase in the myosin-to-actin ratio. Lower thin filament density was calculated to increase thick-to-thin filament spacing in vivo from 17 to 23 nm. Decreased density is postulated to promote earlier cross-bridge detachment and faster contraction velocity. Atrophic fibers may be more susceptible to sarcomere reloading damage, because force per thin filament is estimated to increase by 23%.
Effects of swimming training on three superoxide dismutase isoenzymes in mouse tissues
Authors: Nakao Chitose , Ookawara Tomomi , Kizaki Takako , Oh-Ishi Shuji , Miyazaki Hiromi , Haga Shuhkoh , Sato Yuzo , Ji Li Li , Ohno Hideki
Published: December 2017

The purpose of the present study was to investigate the effects of swimming training on the changes in three superoxide dismutase (SOD) isoenzymes in mice. The trained mice underwent a 6-wk swimming program (1 h/day, 5 days/wk) in water at 35–36°C. Immunoreactive extracellular SOD (EC-SOD), copper- and zinc-containing SOD (CuZn-SOD), and manganese-containing SOD (Mn-SOD) contents and their mRNA abundance were determined in serum, heart, lung, liver, kidney, and gastrocnemius muscle. EC-SOD content in liver and kidney was significantly increased with training. After training, CuZn-SOD content rose significantly only in kidney but decreased significantly in heart, lung, and liver. Mn-SOD content showed a significant increase in lung, kidney, and skeletal muscle but a significant decrease in liver. In most tissues, however, the changes in SOD isoenzyme contents were not concomitant with those in their mRNA levels. The results obtained thus suggest that, except for kidney, the responses in mouse tissues of three SOD isoenzymes (protein levels and mRNA abundance) to swimming training are different and that kidney may be one of the most sensitive organs to adapt to oxidative stress during physical training, although the mechanism remains vague.
Cutaneous blood flow during exercise is higher in endurance-trained humans
Authors: Fritzsche Ricardo G. , Coyle Edward F.
Published: December 2017

This study determined whether cutaneous blood flow during exercise is different in endurance-trained (Tr) compared with untrained (Untr) subjects. Ten Tr and ten Untr men (62.4 ± 1.7 and 44.2 ± 1.8 ml ⋅ kg− 1 ⋅ min− 1, respectively; P < 0.05) underwent three 20-min cycling-exercise bouts at 50, 70, and 90% peak oxygen uptake in this order, with 30 min rest in between. The environmental conditions were neutral (∼23–24°C, 50% relative humidity, front and back fans at 2.5 m/s). Because of technical difficulties, only seven Tr and seven Untr subjects completed all forearm blood flow and laser-Doppler cutaneous blood flow (CBF) measurements. Albeit similar at rest, at the end of all three exercise bouts, forearm blood flow was ∼40% higher in Tr compared with Untr subjects (50%: 4.64 ± 0.50 vs. 3.17 ± 0.20, 70%: 6.17 ± 0.61 vs. 4.41 ± 0.37, 90%: 6.77 ± 0.62 vs. 5.01 ± 0.37 ml ⋅ 100 ml− 1 ⋅ min− 1, respectively; n = 7; all P < 0.05). CBF was also higher in Tr compared with Untr subjects at all relative intensities ( n = 7; all P < 0.05). However, esophageal temperature was not different in Tr compared with Untr subjects at the end of any of the aforementioned exercise bouts (50%: 37.8 ± 0.1 vs. 37.9 ± 0.1°C, 70%: 38.1 ± 0.1 vs. 38.1 ± 0.1°C, and 90%: 38.8 ± 0.1 vs. 38.6 ± 0.1°C, respectively). We conclude that a higher CBF may allow Tr subjects to achieve an esophageal temperature similar to that of Untr, despite their higher metabolic rates and thus higher heat production rates, during exercise at 50–90% peak oxygen uptake.
Mechanical properties of the tracheal mucosal membrane in the rabbit. II. Morphometric analysis
Authors: Wang Lu , Pinder Kenneth L. , Bert Joel L. , Okazawa Mitsushi , Paré Peter D.
Published: December 2017

Folding of the airway mucosal membrane provides a mechanical load that impedes airway smooth muscle contraction. Mechanical testing of rabbit tracheal mucosal membrane showed that the membrane is stiffer in the longitudinal than in the circumferential direction of the airway. To explain this difference in the mechanical properties, we studied the morphological structure of the rabbit tracheal mucosal membrane in both longitudinal and circumferential directions. The collagen fibers were found to form a random meshwork, which would not account for differences in stiffness in the longitudinal and circumferential directions. The volume fraction of the elastic fibers was measured using a point-counting technique. The orientation of the elastic fibers in the tissue samples was measured using a new method based on simple geometry and probability. The results showed that the volume fraction of the elastic fibers in the rabbit tracheal mucosal membrane was ∼5% and that the elastic fibers were mainly oriented in the longitudinal direction. Age had no statistically significant effect on either the volume fraction or the orientation of the elastic fibers. Linear correlations were found between the steady-state stiffness and the quantity of the elastic fibers oriented in the direction of testing.
Regional ventilation-perfusion distribution is more uniform in the prone position
Authors: Mure Margareta , Domino Karen B. , Lindahl Sten G. E. , Hlastala Michael P. , Altemeier William A. , Glenny Robb W.
Published: December 2017

The arterial blood[Formula: see text] is increased in the prone position in animals and humans because of an improvement in ventilation (V˙a) and perfusion (Q˙) matching. However, the mechanism of improvedV˙a/Q˙ is unknown. This experiment measured regionalV˙a/Q˙ heterogeneity and the correlation between V˙a andQ˙ in supine and prone positions in pigs. Eight ketamine-diazepam-anesthetized, mechanically ventilated pigs were studied in supine and prone positions in random order. RegionalV˙a and Q˙ were measured using fluorescent-labeled aerosols and radioactive-labeled microspheres, respectively. The lungs were dried at total lung capacity and cubed into 603–967 small (∼1.7-cm3) pieces. In the prone position the homogeneity of the ventilation distribution increased ( P = 0.030) and the correlation betweenV˙a and Q˙ increased (correlation coefficient = 0.72 ± 0.08 and 0.82 ± 0.06 in supine and prone positions, respectively, P = 0.03). The homogeneity of the V˙a/Q˙distribution increased in the prone position ( P = 0.028). We conclude that the improvement inV˙a/Q˙ matching in the prone position is secondary to increased homogeneity of theV˙a distribution and increased correlation of regional V˙a andQ˙.
Interaction between left and right intercostal muscles in airway pressure generation
Authors: Cappello Matteo , de Troyer André
Published: December 2017

The interactions between the different rib cage inspiratory muscles in the generation of pleural pressure remain largely unknown. In the present study, we have assessed in dogs the interactions between the parasternal intercostals and the interosseous intercostals situated on the right and left sides of the sternum. For each set of muscles, the changes in airway opening pressure (ΔPao) obtained during separate right and left activation were added, and the calculated values (predicted ΔPao) were then compared with the ΔPao values obtained during symmetric, bilateral activation (measured ΔPao). When the parasternal intercostals in one or two interspaces were activated, the measured ΔPao was commonly greater than the predicted value. The difference, however, was only 10%. When the interosseous intercostals were activated, the measured ΔPao was nearly equal to the predicted value. These observations strengthen our previous conclusion that the pressure changes produced by the rib cage inspiratory muscles are essentially additive. As a corollary, the rib cage can be considered as a linear elastic structure over a wide range of distortion.
In vivo estimation of contraction velocity of human vastus lateralis muscle during “isokinetic” action
Authors: Ichinose Y. , Kawakami Y. , Ito M. , Kanehisa H. , Fukunaga T.
Published: December 2017

To determine the shortening velocities of fascicles of the vastus lateralis muscle (VL) during isokinetic knee extension, six male subjects were requested to extend the knee with maximal effort at angular velocities of 30 and 150°/s. By using an ultrasonic apparatus, longitudinal images of the VL were produced every 30 ms during knee extension, and the fascicle length and angle of pennation were obtained from these images. The shortening fascicle length with extension of the knee (from 98 to 13° of knee angle; full extension = 0°) was greater (43 mm) at 30°/s than at 150°/s (35 mm). Even when the angular velocity remained constant during the isokinetic range of motion, the fascicle velocity was found to change from 39 to 77 mm/s at 150°/s and from 6 to 19 mm/s at 30°/s. The force exerted by a fascicle changed with the length of the fascicle at changing angular velocities. The peak values of fascicle force and velocity were observed at ∼90 mm of fascicle length. In conclusion, even if the angular velocity of knee extension is kept constant, the shortening velocity of a fascicle is dependent on the force applied to the muscle-tendon complex, and the phenomenon is considered to be caused mainly by the elongation of the elastic element (tendinous tissue).
Cellular adaptations in fat tissue of exercise-trained miniature swine: role of excess energy intake
Authors: Carey Gale B.
Published: December 2017

This study examined the influence of energy expenditure and energy intake on cellular mechanisms regulating adipose tissue metabolism. 1 Twenty-four swine were assigned to restricted-fed sedentary, restricted-fed exercise-trained, full-fed sedentary, or full-fed exercise-trained groups. After 3 mo of treatment, adipocytes were isolated and adipocyte size, adenosine A1receptor characteristics, and lipolytic sensitivity were measured. Swine were infused with epinephrine during which adipose tissue extracellular adenosine, plasma fatty acids, and plasma glycerol were measured. Results revealed that adipocytes isolated from restricted-fed exercised swine had a smaller diameter, a lower number of A1receptors, and a greater sensitivity to lipolytic stimulation, compared with adipocytes from full-fed exercised swine. Extracellular adenosine levels were transiently increased on infusion of epinephrine in adipose tissue of restricted-fed exercised but not full-fed exercised swine. These results suggest a role for adenosine in explaining the discrepancy between in vitro and in vivo lipolysis findings and underscore the notion that excess energy intake dampens the lipolytic sensitivity of adipocytes to β-agonists and adenosine, even if accompanied by exercise training.
Effects of spaceflight and thyroid deficiency on hindlimb development. I. Muscle mass and IGF-I expression
Authors: Adams G. R. , McCue S. A. , Bodell P. W. , Zeng M. , Baldwin K. M.
Published: December 2017

Thyroid deficiency (TD) in neonatal rats causes reduced growth of skeletal muscle that is disproportionately greater than that for other tissues (G. R. Adams, S. A. McCue, M. Zeng, and K. M. Baldwin. Am. J. Physiol. Regulatory Integrative Comp. Physiol. 276: R954–R961, 1999). TD depresses plasma insulin-like growth factor I (IGF-I) levels, suggesting a mechanism for this effect. We hypothesized that TD and exposure to spaceflight (SF) would interact to reduce skeletal muscle growth via a reduction in IGF-I levels. Neonatal rats were flown in space for 16 days. There was a similar, nonadditive reduction in the growth of the body (∼50%) and muscle weight (fast muscles, ∼60%) with either TD or SF. In the soleus muscle, either SF or TD alone resulted in growth reductions that were augmented by SF-TD interactions. There were strong correlations between 1) muscle mass and muscle IGF-I levels and 2) circulating IGF-I and body weight. These results indicate that either hypothyroidism or exposure to SF will limit the somatic and muscle-specific growth of neonatal rats. The impact of these perturbations on skeletal muscle growth is relatively greater than the effect on somatic growth. The mechanisms by which either TD or SF impact growth appear to have a common pathway involving the control of plasma and muscle IGF-I concentrations.
Carotid baroreflex control of heart rate and blood pressure during ES leg cycling in paraplegics
Authors: Raymond Jacqui , Davis Glen M. , van der Plas Martinus N. , Groeller Herbert , Simcox Scott
Published: December 2017

This study investigated control of heart rate (HR) and mean arterial pressure (MAP) at rest and during electrical stimulation (ES) leg cycling exercise (LCE) in paraplegics (Para). Seven men with complete spinal lesions (T5–T11) and six able-bodied (AB) men participated in this study. Beat-to-beat changes in HR and MAP were recorded during carotid sinus perturbation. Carotid baroreflex function curves were derived at rest and during ES-LCE for Para and during voluntary cycling (Vol) for AB. From rest to ES-LCE, oxygen uptake (V˙o 2) increased (by 0.43 l/min) and HR rose (by 11 beats/min), yet MAP remained unchanged. In AB, Vol increased V˙o 2 (by 0.53 l/min), HR (by 22 beats/min), and MAP (by 8 mmHg). ES-LCE did not alter the carotid sinus pressure (CSP)-MAP relationship, but it displaced the CSP-HR relationship upward relative to rest. No rightward shift was observed during ES-LCE. Vol by AB produced an upward and rightward displacement of the CSP-MAP and CSP-HR relationships relative to rest. These findings suggested that the carotid sinus baroreflex was not reset during ES-LCE in Para.
Pulmonary vascular response of the coati to chronic hypoxia
Authors: Hanson Wendy L. , Boggs Dona F. , Kay J. Michael , Hofmeister Stephen E. , Okada Osamu , Wagner Wiltz W.
Published: December 2017

The unusually muscular pulmonary arteries normally present in cattle and swine residing at low altitude are associated with a rapid development of severe pulmonary hypertension when those animals are moved to high altitude. Because these species lack collateral ventilation, they appear to have an increased dependence on hypoxic vasoconstriction to maintain normal ventilation-perfusion balance, which, in turn, maintains thickened arterial walls. The only other species known to lack collateral ventilation is the coati, which, similarly, has thick-walled pulmonary arteries. We tested the hypothesis that coatis will develop severe high-altitude pulmonary hypertension by exposing six of these animals ( Nasua narica) to a simulated altitude of 4,900 m for 6 wk. After the exposure, pulmonary arterial pressures were hardly elevated, right ventricular hypertrophy was minimal, there was no muscularization of pulmonary arterioles, and, most surprising of all, there was a decrease in medial thickness of muscular pulmonary arteries. These unexpected results break a consistent cross-species pattern in which animals with thick muscular pulmonary arteries at low altitude develop severe pulmonary hypertension at high altitude.