bluuebunny/crossref_metadata_2025 huggingface dataset:
Chronic and acute exercise do not alter Ca2+regulatory systems and ectonucleotidase activities in rat heart
Authors: Delgado Jerónimo , Saborido Ana , Morán María , Megías Alicia
Published: December 2017

The purpose of this investigation was to examine the effects of chronic and acute exercise on the main components involved in excitation-contraction coupling and relaxation in rat heart. Sixty male Wistar rats were divided into a sedentary (S) and three 12-wk treadmill-trained groups (T-1, moderate intensity; T-2, high intensity; T-3, interval running). After 12-wk, 15 rats from the S group and 15 rats from the T-2 group were subjected to a single treadmill-exercise session until exhaustion before being killed at 0, 24, or 48 h (acute exercise). The remaining animals were killed 48 h after the last standard exercise session (chronic exercise). The efficacy of the training programs was confirmed by an increase in treadmill endurance time and in skeletal muscle citrate synthase activity. None of the exercise programs modified heart weight or cardiac oxidative capacity. [3H]PN200–110 and [3H]ryanodine binding to cardiac homogenates indicated that the density of L-type and sarcoplasmic reticulum (SR) Ca2+channels was the same in S and trained rats. The SR Ca2+-ATPase activity was also unmodified. Finally, the activities of the ectoenzymes Mg2+-ATPase and 5′-nucleotidase, which are involved in degradation of extracellular nucleotides, were not affected by either of the running programs. After the acute exercise session, no changes were detected in either of the tested parameters in heart homogenates of S and T-2 animals. We conclude that neither treadmill-exercise training for 12 wk nor exhaustive exercise alters the density of Ca2+channels involved in excitation-contraction coupling or the SR Ca2+-ATPase and the ectonucleotidase activities in rat heart.
Wall thickness referenced to myocardial volume: a new noninvasive framework for cardiac mechanics
Authors: Denslow Stewart , Balaji Seshadri , Hewett Kenneth W.
Published: December 2017

Dimensional variables measured for study of left ventricular mechanics are subject to errors arising from difficulty in determining zero-stress dimensions for use as a reference. Based on a method validated for measurements within individuals, we have devised an approach that facilitates comparison between individuals while minimizing random scatter. We define an exact mathematical index of strain, ln( h0/ h), using wall thickness ( h) referenced to extrapolated wall thickness at zero-luminal volume ( h0). Noninvasive data from rabbits, pigs, and humans all yielded highly similar myocardial stress, ln( h0/ h), and work values. The stress-ln( h0/ h) relationship during afterload variation was constant among individual pigs with a twofold variation in ventricular mass. Stress-ln( h0/ h) data from our analysis displayed lower scatter than either pressure-volume data normalized to myocardial mass or stress-ln( h0/ h) data referenced to end-diastolic dimensions. A Frank-Starling-like curve with high correlation ( r2= 0.96) was constructed from single points from different pigs, suggesting a low level of size and intersubject scatter. This method offers high precision for noninvasive characterization of ventricular and myocardial mechanics and for comparisons between subjects and between species.
Effects of endurance exercise training on muscle glycogen accumulation in humans
Authors: Greiwe Jeffrey S. , Hickner Robert C. , Hansen Polly A. , Racette Susan B. , Chen May M. , Holloszy John O.
Published: December 2017

The purpose of this investigation was to determine whether endurance exercise training increases the ability of human skeletal muscle to accumulate glycogen after exercise. Subjects (4 women and 2 men, 31 ± 8 yr old) performed high-intensity stationary cycling 3 days/wk and continuous running 3 days/wk for 10 wk. Muscle glycogen concentration was measured after a glycogen-depleting exercise bout before and after endurance training. Muscle glycogen accumulation rate from 15 min to 6 h after exercise was twofold higher ( P < 0.05) in the trained than in the untrained state: 10.5 ± 0.2 and 4.5 ± 1.3 mmol ⋅ kg wet wt−1⋅ h−1, respectively. Muscle glycogen concentration was higher ( P < 0.05) in the trained than in the untrained state at 15 min, 6 h, and 48 h after exercise. Muscle GLUT-4 content after exercise was twofold higher ( P < 0.05) in the trained than in the untrained state (10.7 ± 1.2 and 4.7 ± 0.7 optical density units, respectively) and was correlated with muscle glycogen concentration 6 h after exercise ( r = 0.64, P < 0.05). Total glycogen synthase activity and the percentage of glycogen synthase I were not significantly different before and after training at 15 min, 6 h, and 48 h after exercise. We conclude that endurance exercise training enhances the capacity of human skeletal muscle to accumulate glycogen after glycogen-depleting exercise.
Effect of diet on fat cell size and hormone-sensitive lipase activity
Authors: Berger Joshua J. , Barnard R. James
Published: December 2017

This study was designed to examine the relationship between diet-induced insulin resistance/hyperinsulinemia, fat cell hypertrophy, and hormone-sensitive lipase (HSL) to elucidate whether an attenuated HSL activity leads to obesity. Female Fischer 344 rats were fed either a low-fat, complex-carbohydrate diet or a high-fat, refined-sugar (HFS) diet for 2 wk, 2 mo, or 6 mo. Adipose tissue morphology and HSL activity as well as plasma free fatty acid and glycerol levels were determined at these times. No differences between groups were seen after 2 wk except the previously reported hyperinsulinemia in the HFS animals. At both 2 and 6 mo, the HFS animals demonstrated adipocyte hypertrophy. Basal and stimulated HSL activities and plasma glycerol were significantly elevated in the HFS group. There was a positive correlation between adipocyte size and HSL activity for both basal and stimulated states. These results demonstrate that an attenuated HSL activity is not observed with the onset of insulin resistance/hyperinsulinemia and therefore does not play a role in the development of obesity.
Increased extracellular water compartment, relative to intracellular water compartment, after weight reduction
Authors: Lichtenbelt Wouter D. Van Marken , Fogelholm Mikael
Published: December 2017

The hydration of fat free mass (FFM) and extracellular (ECW) and intracellular water (ICW) compartments were studied in 30 obese premenopausal women before and after a 3-mo weight-reduction program and again after a 9-mo weight-maintenance program. Body fat was determined by a four-compartment model. Total body water and ECW were determined by deuterium dilution and bromide dilution, respectively. After the weight-reduction period, mean weight loss was 12.8 kg, and body fat was reduced on average by 10.9 kg. During weight maintenance, changes in body mass and body fat were not significant. Before weight reduction, mean ECW/ICW ratio was relatively high (0.78 ± 0.10). During the the study, total body water and ICW did not change significantly. ECW did not change significantly after weight reduction, but 12 mo after the start ECW was significantly increased by 1 liter. The ECW/ICW ratio increased to 0.87 ± 0.12 ( month 12). The hydration of the FFM increased from 74 ± 1 to 77 ± 2% during the weight reduction and remained elevated during weight maintenance. In conclusion, the ECW/ICW ratio and the hydration of the FFM, did not normalize during weight reduction and weight maintenance.
Isoproterenol improves ability of lung to clear edema in rats exposed to hyperoxia
Authors: Saldías F. J. , Comellas A. , Ridge K. M. , Lecuona E. , Sznajder J. I.
Published: December 2017

Exposure of adult rats to 100% O2results in lung injury and decreases active sodium transport and lung edema clearance. It has been reported that β-adrenergic agonists increase lung edema clearance in normal rat lungs by upregulating alveolar epithelial Na+-K+-ATPase function. This study was designed to examine whether isoproterenol (Iso) affects lung edema clearance in rats exposed to 100% O2for 64 h. Active Na+transport and lung edema clearance decreased by ∼44% in rats exposed to acute hyperoxia. Iso (10−6M) increased the ability of the lung to clear edema in room-air-breathing rats (from 0.50 ± 0.02 to 0.99 ± 0.05 ml/h) and in rats exposed to 100% O2(from 0.28 ± 0.03 to 0.86 ± 0.09 ml/h; P < 0.001). Disruption of intracellular microtubular transport of ion-transporting proteins by colchicine (0.25 mg/100 g body wt) inhibited the stimulatory effects of Iso in hyperoxia-injured rat lungs, whereas the isomer β-lumicolchicine, which does not affect microtubular transport, did not inhibit active Na+transport stimulated by Iso. Accordingly, Iso restored the lung’s ability to clear edema after hyperoxic lung injury, probably by stimulation of the recruitment of ion-transporting proteins (Na+-K+-ATPase) from intracellular pools to the plasma membrane in rat alveolar epithelium.
Carotid baroreflex function during prolonged exercise
Authors: Norton K. H. , Gallagher K. M. , Smith S. A. , Querry R. G. , Welch-O’Connor R. M. , Raven P. B.
Published: December 2017

The present investigation was designed to uncouple the hemodynamic physiological effects of thermoregulation from the effects of a progressively increasing central command activation during prolonged exercise. Subjects performed two 1-h bouts of leg cycling exercise with 1) no intervention and 2) continuous infusion of a dextran solution to maintain central venous pressure constant at the 10-min pressure. Volume infusion resulted in a significant reduction in the decrement in mean arterial pressure seen in the control exercise bout (6.7 ± 1.8 vs. 11.6± 1.3 mmHg, respectively). However, indexes of central command such as heart rate and ratings of perceived exertion rose to a similar extent during both exercise conditions. In addition, the carotid-cardiac baroreflex stimulus-response relationship, as measured by using the neck pressure-neck suction technique, was reset from rest to 10 min of exercise and was further reset from 10 to 50 min of exercise in both exercise conditions, with the operating point being shifted toward the reflex threshold. We conclude that the progressive resetting of the carotid baroreflex and the shift of the reflex operating point render the carotid-cardiac reflex ineffectual in counteracting the continued decrement in mean arterial pressure that occurs during the prolonged exercise.
Microdialysis and the measurement of muscle interstitial K+ during rest and exercise in humans
Authors: Green Simon , Bülow Jens , Saltin Bengt
Published: December 2017

The purpose of this study was to examine whether microdialysis and the internal reference thallium-201 (201Tl) could accurately measure muscle interstitial K+([Formula: see text]) before, during, and after exercise. The relative loss of201Tl and simultaneous relative recovery of K+ were measured in vitro for 12 microdialysis probes that were bathed in Ringer acetate medium and perfused at various flows (3–10 μl/min).201Tl loss was linearly related to K+ recovery, and their level of agreement was not different from zero. Microdialysis and201Tl were then used to measure[Formula: see text] in the gastrocnemius medialis muscle of four humans during rest and static plantar flexion exercise. At rest, [Formula: see text] was 3.9–4.3 mmol/l when the perfusate flow was 2 or 5 μl/min. During exercise,[Formula: see text] increased from 6.9 ± 0.4 to 7.5 ± 0.3 mmol/l at low to high intensity and declined to 5.2 ± 0.3 mmol/l after exercise. These results suggest that large changes in[Formula: see text] in human skeletal muscle can be accurately measured by using microdialysis and201Tl.
Impact of acute exercise intensity on pulsatile growth hormone release in men
Authors: Pritzlaff Cathy J. , Wideman Laurie , Weltman Judy Y. , Abbott Robert D. , Gutgesell Margaret E. , Hartman Mark L. , Veldhuis Johannes D. , Weltman Arthur
Published: December 2017

To investigate the effects of exercise intensity on growth hormone (GH) release, 10 male subjects were tested on 6 randomly ordered occasions [1 control condition (C), 5 exercise conditions (Ex)]. Serum GH concentrations were measured in samples obtained at 10-min intervals between 0700 and 0900 (baseline) and 0900 and 1300 (exercise+ recovery). Integrated GH concentrations (IGHC) were calculated by trapezoidal reconstruction. During Ex subjects exercised for 30 min (0900–0930) at one of the following intensities [normalized to the lactate threshold (LT)]: 25 and 75% of the difference between LT and rest (0.25LT and 0.75LT, respectively), at LT, and at 25 and 75% of the difference between LT and peak (1.25LT and 1.75LT, respectively). No differences were observed among conditions for baseline IGHC. Exercise+recovery IGHC (mean ± SE: C = 250 ± 60; 0.25LT = 203 ± 69; 0.75LT = 448 ± 125; LT = 452 ± 119; 1.25LT = 512 ± 121; 1.75LT = 713 ± 115 μg ⋅ l−1 ⋅ min−1) increased linearly with increasing exercise intensity ( P < 0.05). Deconvolution analysis revealed that increasing exercise intensity resulted in a linear increase in the mass of GH secreted per pulse and GH production rate [production rate increased from 16.5 ± 4.5 (C) to 32.1 ± 5.2 μg ⋅ distribution volume−1 ⋅ min−1(1.75LT), P < 0.05], with no changes in GH pulse frequency or half-life of elimination. We conclude that the GH secretory response to exercise is related to exercise intensity in a linear dose-response pattern in young men.
Human fetuses have nonlinear cardiac dynamics
Authors: Groome Lynn J. , Mooney Donna M. , Holland Scherri B. , Smith Lisa A. , Atterbury Jana L. , Loizou Philip C.
Published: December 2017

Approximate entropy (ApEn) is a statistic that quantifies regularity in time series data, and this parameter has several features that make it attractive for analyzing physiological systems. In this study, ApEn was used to detect nonlinearities in the heart rate (HR) patterns of 12 low-risk human fetuses between 38 and 40 wk of gestation. The fetal cardiac electrical signal was sampled at a rate of 1,024 Hz by using Ag-AgCl electrodes positioned across the mother’s abdomen, and fetal R waves were extracted by using adaptive signal processing techniques. To test for nonlinearity, ApEn for the original HR time series was compared with ApEn for three dynamic models: temporally uncorrelated noise, linearly correlated noise, and linearly correlated noise with nonlinear distortion. Each model had the same mean and SD in HR as the original time series, and one model also preserved the Fourier power spectrum. We estimated that noise accounted for 17.2–44.5% of the total between-fetus variance in ApEn. Nevertheless, ApEn for the original time series data still differed significantly from ApEn for the three dynamic models for both group comparisons and individual fetuses. We concluded that the HR time series, in low-risk human fetuses, could not be modeled as temporally uncorrelated noise, linearly correlated noise, or static filtering of linearly correlated noise.
Ratio of active to passive muscle shortening in the canine diaphragm
Authors: Boriek Aladin M. , Rodarte Joseph R. , Wilson Theodore A.
Published: December 2017

Active and passive shortening of muscle bundles in the canine diaphragm were measured with the objective of testing a consequence of the minimal-work hypothesis: namely, that the ratio of active to passive shortening is the same for all active muscles. Lengths of six muscle bundles in the costal diaphragm and two muscle bundles in the crural diaphragm of each of four bred-for-research beagle dogs were measured by the radiopaque marker technique during the following maneuvers: a passive deflation maneuver from total lung capacity to functional residual capacity, quiet breathing, and forceful inspiratory efforts against an occluded airway at different lung volumes. Shortening per liter increase in lung volume was, on average, 70% greater during quiet breathing than during passive inflation in the prone posture and 40% greater in the supine posture. For the prone posture, the ratio of active to passive shortening was larger in the ventral and midcostal diaphragm than at the dorsal end of the costal diaphragm. For both postures, active shortening during quiet breathing was poorly correlated with passive shortening. However, shortening during forceful inspiratory efforts was highly correlated with passive shortening. The average ratios of active to passive shortening were 1.23 ± 0.02 and 1.32 ± 0.03 for the prone and supine postures, respectively. These data, taken together with the data reported in the companion paper (T. A. Wilson, M. Angelillo, A. Legrand, and A. De Troyer, J. Appl. Physiol. 87: 554-560, 1999), support the hypothesis that, during forceful inspiratory efforts, the inspiratory muscles drive the chest wall along the minimal-work trajectory.
Effects of continuous negative airway pressure on lung volume and respiratory resistance
Authors: Lorino Anne Marie , Hamoudi Kamel , Lofaso Frédéric , Dahan Estelle , Mariette Christian , Harf Alain , Lorino Hubert
Published: December 2017

This study was designed to determine the responses of lung volume and respiratory resistance (Rrs) to decreasing levels of continuous negative airway pressure (CNAP). Twenty normal subjects were studied in the basal state and under CNAP levels of −5, −10, and −15 hPa. Rrs was measured by the forced oscillation technique (4–32 Hz). End-expiratory lung volume (EELV) and tidal volume (Vt) were measured by whole body plethysmography. Rrs was extrapolated to 0 Hz (R0) and estimated at 16 Hz (R16) by linear regression analysis of Rrs vs. frequency. Specific Rrs, SR0and SR16, were then calculated as R0(EELV + Vt/2) and R16(EELV + Vt/2), respectively. EELV significantly decreased, whereas R0, R16, SR0, and SR16significantly increased, as the CNAP level decreased ( P < 0.0001 for all). At the lowest CNAP level, R0and R16reached 198 ± 13 and 175 ± 9% of their respective basal values. The CNAP-induced increase in R0was significantly higher than that in R16( P < 0.004). Our results demonstrate that the CNAP-induced increase in Rrs does not result from a direct lung volume effect only and strongly suggest the involvement of other factors affecting both intrathoracic and extrathoracic airway caliber.
Effect of epinephrine on alveolar liquid clearance in the rat
Authors: Charron Paul D. , Fawley J. Phillip , Maron Michael B.
Published: December 2017

Endogenous epinephrine has been found to increase alveolar liquid clearance (ALC) in several pulmonary edema models. In this study, we infused epinephrine intravenously for 1 h in anesthetized rats to produce plasma epinephrine concentrations commonly observed in this species under stressful conditions and measured ALC by mass balance. Epinephrine increased ALC from 31.5 ± 3.2 to 48.9 ± 1.1 (SE)% of the instilled volume ( P < 0.05). The increased ALC was prevented by either propranolol or amiloride. To determine whether ALC returns to normal after plasma epinephrine concentration normalizes, we measured ALC 2 h after stopping an initial 1-h epinephrine infusion and found ALC to be at baseline values. Finally, to determine whether desensitization of the liquid clearance response occurs, we evaluated the effects of both repeated 1-h infusions and a continuous 4-h infusion of epinephrine on ALC and found no reduction in ALC under either condition. We conclude that epinephrine increases ALC by stimulating β-adrenoceptors and sodium transport, that the increase is reversible once plasma epinephrine concentration normalizes, and that desensitization of the ALC response does not appear to occur after 4 h of continuous epinephrine exposure.
Immune changes in humans during cold exposure: effects of prior heating and exercise
Authors: Brenner I. K. M. , Castellani J. W. , Gabaree C. , Young A. J. , Zamecnik J. , Shephard R. J. , Shek P. N.
Published: December 2017

This study examined the immunological responses to cold exposure together with the effects of pretreatment with either passive heating or exercise (with and without a thermal clamp). On four separate occasions, seven healthy men [mean age 24.0 ± 1.9 (SE) yr, peak oxygen consumption = 45.7 ± 2.0 ml ⋅ kg−1 ⋅ min−1] sat for 2 h in a climatic chamber maintained at 5°C. Before exposure, subjects participated in one of four pretreatment conditions. For the thermoneutral control condition, subjects remained seated for 1 h in a water bath at 35°C. In another pretreatment, subjects were passively heated in a warm (38°C) water bath for 1 h. In two other pretreatments, subjects exercised for 1 h at 55% peak oxygen consumption (once immersed in 18°C water and once in 35°C water). Core temperature rose by 1°C during passive heating and during exercise in 35°C water and remained stable during exercise in 18°C water (thermal clamping). Subsequent cold exposure induced a leukocytosis and granulocytosis, an increase in natural killer cell count and activity, and a rise in circulating levels of interleukin-6. Pretreatment with exercise in 18°C water augmented the leukocyte, granulocyte, and monocyte response. These results indicate that acute cold exposure has immunostimulating effects and that, with thermal clamping, pretreatment with physical exercise can enhance this response. Increases in levels of circulating norepinephrine may account for the changes observed during cold exposure and their modification by changes in initial status.
Chronic exposure to sidestream tobacco smoke augments lung C-fiber responsiveness in young guinea pigs
Authors: Mutoh T. , Bonham A. C. , Kott K. S. , Joad J. P.
Published: December 2017

Children chronically exposed to environmental tobacco smoke (ETS) have more coughs, wheezes, and airway obstruction, which may result in part from stimulation of lung C fibers. We examined the effect of chronic exposure to sidestream tobacco smoke (SS, a surrogate for ETS) on lung C-fiber responsiveness in guinea pigs, in which dynamic compliance (Cdyn), lung resistance, tracheal pressure, arterial blood pressure, and heart rate were also monitored. Guinea pigs were exposed to SS (1 mg/mm3total suspended particulates) or filtered air 5 days/wk from 1 to 6 wk of age. They were then anesthetized, and lung C fibers ( n = 55), identified by a conduction velocity of <2.0 m/s, were tested for responsiveness to chemical and mechanical stimuli. SS exposure doubled C-fiber responsiveness to left atrial capsaicin ( P = 0.02) and lung hyperinflation ( P = 0.03) but had no effect on responsiveness to inhaled capsaicin or bradykinin or on baseline activity. The data indicate that chronically exposing young guinea pigs to SS enhances C-fiber sensitivity to certain stimuli and may help explain respiratory symptoms in children exposed to ETS.
Peroxynitrite induces contractile dysfunction and lipid peroxidation in the diaphragm
Authors: Supinski G. , Stofan D. , Callahan L. A. , Nethery D. , Nosek T. M. , DiMarco A.
Published: December 2017

Peroxynitrite may be generated in and around muscles in several pathophysiological conditions (e.g., sepsis) and may induce muscle dysfunction in these disease states. The effect of peroxynitrite on muscle force generation has not been directly assessed. The purpose of the present study was to assess the effects of peroxynitrite administration on diaphragmatic force-generating capacity in 1) intact diaphragm muscle fiber bundles (to model the effects produced by exposure of muscles to extracellular peroxynitrite) and 2) single skinned diaphragm muscle fibers (to model the effects of intracellular peroxynitrite on contractile protein function) by examining the effects of both peroxynitrite and a peroxynitrite-generating solution, 3-morpholinosydnonimine, on force vs. pCa characteristics. In intact diaphragm preparations, peroxynitrite reduced diaphragm force generation and increased muscle levels of 4-hydroxynonenal (an index of lipid peroxidation). In skinned fibers, both peroxynitrite and 3-morpholinosydnonimine reduced maximum calcium-activated force. These data indicate that peroxynitrite is capable of producing significant diaphragmatic contractile dysfunction. We speculate that peroxynitrite-mediated alterations may be responsible for much of the muscle dysfunction seen in pathophysiological conditions such as sepsis.
Effects of caffeine on neuromuscular function
Authors: Kalmar J. M. , Cafarelli E.
Published: December 2017

This double-blind, repeated-measures study examined the effects of caffeine on neuromuscular function. Eleven male volunteers [22.3 ± 2.4 (SD) yr] came to the laboratory for control, placebo, and caffeine (6 mg/kg dose) trials. Each trial consisted of 10 × 1-ms stimulation of the tibial nerve to elicit maximal H reflexes of the soleus, four attempts at a maximal voluntary contraction (MVC) of the right knee extensors, six brief submaximal contractions, and a 50% MVC held to fatigue. Isometric force and surface electromyographic signals were recorded continuously. The degree of maximal voluntary activation was assessed with the twitch-interpolation technique. Single-unit recordings were made with tungsten microelectrodes during the submaximal contractions. Voluntary activation at MVC increased by 3.50 ± 1.01 (SE) % ( P < 0.01), but there was no change in H-reflex amplitude, suggesting that caffeine increases maximal voluntary activation at a supraspinal level. Neither the force-EMG relationship nor motor unit firing rates were altered by caffeine. Subjects were able to hold a 50% MVC for an average of 66.1 s in the absence of caffeine. Time to fatigue (Tlim) increased by 25.80 ± 16.06% after caffeine administration ( P < 0.05). There was no significant change in Tlim from pretest to posttest in the control or placebo trials. The increase in Tlim was associated with an attenuated decline in twitch amplitude, which would suggest that the mechanism is, at least in part, peripheral.
Slowing and attenuation of baroreflex heart rate control with nitrous oxide in exercising men
Authors: Östlund A. , Linnarsson D.
Published: December 2017

The objective of the present study was to determine whether mild inert-gas narcosis impairs cardiovascular control mechanisms and contributes to the relative bradycardia that occurs in humans exercising in a hyperbaric environment. Eight healthy subjects were exposed to a normoxic 30% nitrous oxide (N2O) mixture and an air control during dynamic exercise of 100-W intensity. Beat-by-beat heart rate (HR) and invasive arterial blood pressure measurements were made. The sensitivity and the response latency of the arterial-cardiac-chronotropic baroreflex were determined from repeated blood pressure and HR transients induced by rapid tilts between the upright and supine posture. A significant increase (37%, P ≤ 0.02) of latency in baroreflex responses was found with 30% N2O, as well as a significant depression (16%, P ≤ 0.05) in baroreflex sensitivity. There were no differences between air and N2O in steady-state HR or arterial pressure. We conclude that mild inert-gas narcosis increases the latency and decreases the gain of HR responses to arterial baroreflex stimuli, but this cannot in itself account for the modest, relative bradycardia observed during moderately heavy exercise in a normoxic, hyperbaric environment.
Familial aggregation ofV˙o 2 max response to exercise training: results from the HERITAGE Family Study
Authors: Bouchard Claude , An Ping , Rice Treva , Skinner James S. , Wilmore Jack H. , Gagnon Jacques , Pérusse Louis , Leon Arthur S. , Rao D. C.
Published: December 2017

The aim of this study was to test the hypothesis that individual differences in the response of maximal O2 uptake (V˙o 2 max) to a standardized training program are characterized by familial aggregation. A total of 481 sedentary adult Caucasians from 98 two-generation families was exercise trained for 20 wk and was tested for V˙o 2 max on a cycle ergometer twice before and twice after the training program. The mean increase inV˙o 2 max reached ∼400 ml/min, but there was considerable heterogeneity in responsiveness, with some individuals experiencing little or no gain, whereas others gained >1.0 l/min. An ANOVA revealed that there was 2.5 times more variance between families than within families in theV˙o 2 max response variance. With the use of a model-fitting procedure, the most parsimonious models yielded a maximal heritability estimate of 47% for the V˙o 2 max response, which was adjusted for age and sex with a maternal transmission of 28% in one of the models. We conclude that the trainability ofV˙o 2 max is highly familial and includes a significant genetic component.
Aerobically generated CO2stored during early exercise
Authors: Chuang Ming-Lung , Ting Hua , Otsuka Toshihiro , Sun Xing-Guo , Chiu Frank Y. L. , Beaver William L. , Hansen James E. , Lewis David A. , Wasserman Karlman
Published: December 2017

Previous studies have shown that a metabolic alkalosis develops in the muscle during early exercise. This has been linked to phosphocreatine hydrolysis. Over a similar time frame, the femoral vein blood pH and plasma K+ and[Formula: see text] concentrations increase without an increase in [Formula: see text]. Thus CO2 from aerobic metabolism is converted to [Formula: see text] rather than being eliminated by the lungs. The purpose of this study was to quantify the increase in early CO2 stores and the component due to the exercise-induced metabolic alkalosis (E-I Alk). To avoid masking the increase in CO2 stores by CO2 released as[Formula: see text] buffers lactic acid, the transient increase in CO2 stores was measured only for work rates (WRs) below the lactic acidosis threshold (LAT). The increase in CO2 stores was evident at the airway starting at ∼15 s; the increase reached a peak at ∼60 s and was complete by ∼3 min of exercise. The increase in CO2 stores was greater, but the kinetics were unaffected at the higher WR. Three components of the change in aerobically generated CO2 stores were considered relevant: the carbamate component of the Haldane effect, the increase in CO2 stores due to increase in tissue [Formula: see text], and the E-I Alk. The Haldane effect was calculated to be ∼5%. Physically dissolved CO2 in the tissues was ∼30% of the store increase. The remaining E-I Alk CO2 stores averaged 61 and 68% for 60 and 80% LAT WRs, respectively. The kinetics of O2 uptake correlated with the time course of the increase in CO2stores; the size of the O2 deficit correlated with the size of the E-I Alk component of the CO2 stores. We conclude that a major component of the aerobically generated increase in CO2 stores is the new[Formula: see text] generated as phosphocreatine is converted to creatine.
Hypertrophy of skeletal muscle in diabetic rats in response to chronic resistance exercise
Authors: Farrell Peter A. , Fedele Mark J. , Hernandez Jazmir , Fluckey James D. , Miller John L. , Lang Charles H. , Vary Thomas C. , Kimball Scot R. , Jefferson Leonard S.
Published: December 2017

This study had the following objectives: 1) to determine whether diabetic rats could increase muscle mass due to a physiological manipulation (chronic resistance exercise), 2) to determine whether exercise training status modifies the effect of the last bout of exercise on elevations in rates of protein synthesis, and 3) to determine whether chronic resistance exercise alters basal glycemia. Groups consisted of diabetic or nondiabetic rats that performed progressive resistance exercise for 8 wk, performed acute resistance exercise, or remained sedentary. Arterial plasma insulin in diabetic groups was reduced by about one-half ( P < 0.05) compared with nondiabetic groups. Soleus and gastrocnemius-plantaris complex muscle wet weights were lower because of diabetes, but in response to chronic exercise these muscles hypertrophied in diabetic (0.028 ± 0.003 vs. 0.032 ± 0.0015 g/cm for sedentary vs. exercised soleus and 0.42 ± 0.068 vs. 0.53 ± 0.041 g/cm for sedentary vs. exercised gastrocnemius-plantaris, both P < 0.05) but not in nondiabetic (0.041 ± 0.0026 vs. 0.042 ± 0.003 g/cm for sedentary vs. exercised soleus and 0.72 ± 0.015 vs. 0.69 ± 0.013 g/cm for sedentary vs. exercised gastrocnemius-plantaris) rats when muscle weight was expressed relative to tibial length or body weight (data not shown). Another group of diabetic rats that lifted heavier weights showed muscle hypertrophy. Rates of protein synthesis were higher in red gastrocnemius in chronically exercised than in sedentary rats: 155 ± 11 and 170 ± 7 nmol phenylalanine incorporated ⋅ g muscle−1⋅ h−1in exercised diabetic and nondiabetic rats vs. 110 ± 14 and 143 ± 7 nmol phenylalanine incorporated ⋅ g muscle−1⋅ h−1in sedentary diabetic and nondiabetic rats. These elevations, however, were lower than in acutely exercised (but untrained) rats: 176 ± 15 and 193 ± 8 nmol phenylalanine incorporated ⋅ g muscle−1⋅ h−1in diabetic and nondiabetic rats. Finally, chronic exercise training in diabetic rats was associated with reductions in basal glycemia, and such reductions did not occur in sedentary diabetic groups. These data demonstrate that, despite lower circulating insulin concentrations, diabetic rats can increase muscle mass in response to a physiological stimulus.
Airway obstruction during exercise and isocapnic hyperventilation in asthmatic subjects
Authors: Suman Oscar E. , Beck Kenneth C. , Babcock Mark A. , Pegelow David F. , Reddan William G.
Published: December 2017

We compared pulmonary mechanics measured during long-term exercise (LTX = 20 min) with long-term isocapnic hyperventilation (LTIH = 20 min) in the same asthmatic individuals ( n = 6). Peak expiratory flow (PEF) and forced expiratory volume in 1 s (FEV1) decreased during LTX (−19.7 and −22.0%, respectively) and during LTIH (−6.66 and 10.9%, respectively). In contrast, inspiratory pulmonary resistance (Rl I) was elevated during LTX (57.6%) but not during LTIH (9.62%). As expected, airway function deteriorated post-LTX and post-LTIH (FEV1 = −30.2 and −21.2%; Rl I = 111.8 and 86.5%, respectively). We conclude that the degree of airway obstruction observed during LTX is of a greater magnitude than that observed during LTIH. Both modes of hyperpnea induced similar levels of airway obstruction in the posthyperpnea period. However, the greater airway obstruction during LTX suggests that a different process may be responsible for the changes in airway function during and after the two modes of hyperpnea. This finding raises questions about the equivalency of LTIH and LTX in the study of airway function during exercise-induced asthma.
Endothelin-1 sensitivity of porcine coronary arteries is reduced by exercise training and is gender dependent
Authors: Jones Allan W. , Rubin Leona J. , Magliola Lawrence
Published: December 2017

We tested the hypothesis that exercise training reduces the sensitivity of coronary smooth muscle to endothelin-1 (ET-1), with the adaptation being greater in male than in female miniature swine. The efficacy of training was similar in males and females. Cumulative ET-1 contractile responses of coronary branches and left circumflex artery were significantly shifted to the right in exercise-trained (Ex) males but not in Ex females. Analyses of the excitatory concentration causing a 50% response (EC50) showed a 1.7- to 2.2-fold shift in Ex males with no change in maximum tension. Nonselective blockade of K-channel activity with tetraethylammonium (TEA; 30–50 mM) significantly shifted the EC50to a lower concentration in both Ex males (1.25-fold) and Ex females (2.2-fold) but not in sedentary (Sed) groups. Females (combined Sed and Ex) exhibited a greater response to TEA than did combined Sed and Ex males. Changes in [32P]phosphatidic acid ([32P]PA) provided an indicator of ET-1-induced phospholipase activity. The magnitude of the [32P]PA response was reduced by Ex in both males and females without affecting the EC50. It is concluded that the contractile sensitivity of coronary arteries to ET-1 is influenced by physical activity in a gender-dependent manner. It is unclear why the contractile sensitivity in females was not reduced by Ex as in the males, because Ex significantly affected responses to TEA and ET-1 stimulation of [32P]PA production in both males and females. A potential gender difference in K-channel function may contribute to this discrepancy.
Effect of negative expiratory pressure on respiratory system flow resistance in awake snorers and nonsnorers
Authors: Tantucci Claudio , Duguet Alexandre , Ferretti Anna , Mehiri Selma , Arnulf Isabelle , Zelter Marc , Similowski Thomas , Derenne Jean-Philippe , Milic-Emili Joseph
Published: December 2017

In spontaneously breathing subjects, intrathoracic expiratory flow limitation can be detected by applying a negative expiratory pressure (NEP) at the mouth during tidal expiration. To assess whether NEP might increase upper airway resistance per se, the interrupter resistance of the respiratory system (Rint,rs) was computed with and without NEP by using the flow interruption technique in 12 awake healthy subjects, 6 nonsnorers (NS), and 6 nonapneic snorers (S). Expiratory flow (V˙) and Rint,rs were measured under control conditions with V˙ increased voluntarily and during random application of brief (0.2-s) NEP pulses from −1 to −7 cmH2O, in both the seated and supine position. In NS, Rint,rs with spontaneous increase inV˙ and with NEP was similar [3.10 ± 0.19 and 3.30 ± 0.18 cmH2O ⋅ l−1 ⋅ s at spontaneous V˙ of 1.0 ± 0.01 l/s and atV˙ of 1.1 ± 0.07 l/s with NEP (−5 cmH2O), respectively]. In S, a marked increase in Rint,rs was found at all levels of NEP ( P < 0.05). Rint,rs was 3.50 ± 0.44 and 8.97 ± 3.16 cmH2O ⋅ l−1 ⋅ s at spontaneous V˙ of 0.81 ± 0.02 l/s and atV˙ of 0.80 ± 0.17 l/s with NEP (−5 cmH2O), respectively ( P < 0.05). With NEP, Rint,rs was markedly higher in S than in NS both seated ( F = 8.77; P < 0.01) and supine ( F = 9.43; P < 0.01). In S,V˙ increased much less with NEP than in NS and was sometimes lower than without NEP, especially in the supine position. This study indicates that during wakefulness nonapneic S have more collapsible upper airways than do NS, as reflected by the marked increase in Rint,rs with NEP. The latter leads occasionally to an actual decrease in V˙ such as to invalidate the NEP method for detection of intrathoracic expiratory flow limitation.
Effects of heavy-resistance training on hormonal response patterns in younger vs. older men
Authors: Kraemer William J. , Häkkinen Keijo , Newton Robert U. , Nindl Bradley C. , Volek Jeff S. , McCormick Matthew , Gotshalk Lincoln A. , Gordon Scott E. , Fleck Steven J. , Campbell Wayne W. , Putukian Margot , Evans William J.
Published: December 2017

To examine the adaptations of the endocrine system to heavy-resistance training in younger vs. older men, two groups of men (30 and 62 yr old) participated in a 10-wk periodized strength-power training program. Blood was obtained before, immediately after, and 5, 15, and 30 min after exercise at rest before and after training and at rest at −3, 0, 6, and 10 wk for analysis of total testosterone, free testosterone, cortisol, growth hormone, lactate, and ACTH analysis. Resting values for insulin-like growth factor (IGF)-I and IGF-binding protein-3 were determined before and after training. A heavy-resistance exercise test was used to evaluate the exercise-induced responses (4 sets of 10-repetition maximum squats with 90 s of rest between sets). Squat strength and thigh muscle cross-sectional area increased for both groups. The younger group demonstrated higher total and free testosterone and IGF-I than the older men, training-induced increases in free testosterone at rest and with exercise, and increases in resting IGF-binding protein-3. With training the older group demonstrated a significant increase in total testosterone in response to exercise stress along with significant decreases in resting cortisol. These data indicate that older men do respond with an enhanced hormonal profile in the early phase of a resistance training program, but the response is different from that of younger men.
Targeted deletion of the neutral endopeptidase gene alters ventilatory responses to acute hypoxia in mice
Authors: Grasemann H. , Lu B. , Jiao A. , Boudreau J. , Gerard N. P. , De Sanctis G. T.
Published: December 2017

Neutral endopeptidase (NEP) is one of the major endopeptidases responsible for the inactivation of substance P in the carotid body, a neurotransmitter shown to be important in the transduction of hypoxic stimuli. Ventilatory responses to acute hypoxia were measured by indirect plethysmography in unanesthetized, unrestrained wild-type mice and in mice in which the NEP gene was deleted (NEP -/-). Ventilation was measured while the animals breathed room air: 12% O2 in N2 and 8% O2 in N2. Deletion of the NEP gene caused marked alterations in both the magnitude and composition of the hypoxic ventilatory response to both 8% O2 in N2 and 12% O2 in N2, compared with the wild-type mice (C57BL/6J) on the same genetic background as the NEP -/- mice. Treatment of C57BL/6J mice with thiorphan, a NEP inhibitor, resulted in a greater ventilatory response to 8% O2 because of a significantly greater shortening of expiratory time. The results of these studies demonstrate that NEP plays an important role in modifying the expression of the ventilatory response to acute hypoxia.
Ozone-induced hyperresponsiveness and blockade of M2 muscarinic receptors by eosinophil major basic protein
Authors: Yost Bethany L. , Gleich Gerald J. , Fryer Allison D.
Published: December 2017

Control of airway smooth muscle is provided by parasympathetic nerves that release acetylcholine onto M3 muscarinic receptors. Acetylcholine release is limited by inhibitory M2 muscarinic receptors. In antigen-challenged guinea pigs, hyperresponsiveness is due to blockade of neuronal M2 receptors by eosinophil major basic protein (MBP). Because exposure of guinea pigs to ozone also causes M2dysfunction and airway hyperresponsiveness, the role of eosinophils in ozone-induced hyperresponsiveness was tested. Animals were exposed to filtered air or to 2 parts/million ozone for 4 h. Twenty-four hours later, the muscarinic agonist pilocarpine no longer inhibited vagally induced bronchoconstriction in ozone-exposed animals, indicating M2 dysfunction. M2 receptor function in ozone-exposed animals was protected by depletion of eosinophils with antibody to interleukin-5 and by pretreatment with antibody to guinea pig MBP. M2 function was acutely restored by removal of MBP with heparin. Ozone-induced hyperreactivity was also prevented by antibody to MBP and was reversed by heparin. These data show that loss of neuronal M2 receptor function after ozone is due to release of eosinophil MBP.
Influence of core temperature on autoresuscitation during repeated exposure to hypoxia in normal rat pups
Authors: Serdarevich Christine , Fewell James E.
Published: December 2017

Failure to autoresuscitate by hypoxic gasping during prolonged sleep apnea has been suggested to play a role in sudden infant death. Furthermore, thermal stress brought about by a contribution of infection, overwrapping, or excessive environmental heating has been shown to be associated with an increased risk of sudden infant death, particularly in prone sleeping infants. The present experiments were carried out on newborn rat pups to investigate the influence of “forced” changes in core temperature on their time to last gasp during a single hypoxic exposure and on their ability to autoresuscitate during repeated exposure to hypoxia. On day 5 or 6 postpartum the pups were placed in a temperature-controlled chamber regulated to 33, 35, 37, 39, or 41°C and exposed to a single period of hypoxia (97% N2-3% CO2) and their time to last gasp was determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnea was determined. Increases in core temperature brought about by changes in ambient temperature from 33 to 41°C decreased the time to last gasp after a single hypoxic exposure and decreased the number of successful autoresuscitations after repeated hypoxic exposures. Thus our data support the hypothesis that forced changes in core temperature brought about by changes in ambient temperature influence protective responses in newborns that may prevent death during hypoxia, as may occur during single or repeated episodes of prolonged sleep apnea.
Endurance exercise causes interaction among stress hormones, cytokines, neutrophil dynamics, and muscle damage
Authors: Suzuki Katsuhiko , Totsuka Manabu , Nakaji Shigeyuki , Yamada Mutsuo , Kudoh Satoru , Liu Qiang , Sugawara Kazuo , Yamaya Kanemitsu , Sato Koki
Published: December 2017

We analyzed adaptation mechanisms regulating systemic inflammatory response of the stressed body by using an experimental challenge of repeated exercise bouts and accompanying muscle inflammation. Eight untrained men bicycled at 90 W for 90 min, 3 days in a row. Exercise induced peripheral neutrophilia with a leftward shift of neutrophil nucleus and neutrophil priming for oxidative activity determined by luminol-dependent chemiluminescence. Plasma growth hormone and interleukin-6 rose significantly after exercise and were closely correlated with the neutrophil responses. Serum creatine kinase and myoglobin levels as muscle damage markers rose after exercise in “delayed onset” and were closely correlated with the preceding neutrophil responses. These exercise-induced responses were strongest on day 1, but the magnitude gradually decreased with progressive daily exercise. In contrast, the magnitude of catecholamine responses to exercise sessions gradually rose, possibly suppressing neutrophil oxidative responses. These results indicate that stress-induced systemic release of bioactive substances may determine neutrophil mobilization and functional status, which then may affect local tissue damage of susceptible organs.
Effect of supplementation with a cysteine donor on muscular performance
Authors: Lands L. C. , Grey V. L. , Smountas A. A.
Published: December 2017

Oxidative stress contributes to muscular fatigue. GSH is the major intracellular antioxidant, the biosynthesis of which is dependent on cysteine availability. We hypothesized that supplementation with a whey-based cysteine donor [Immunocal (HMS90)] designed to augment intracellular GSH would enhance performance. Twenty healthy young adults (10 men, 10 women) were studied presupplementation and 3 mo postsupplementation with either Immunocal (20 g/day) or casein placebo. Muscular performance was assessed by whole leg isokinetic cycle testing, measuring peak power and 30-s work capacity. Lymphocyte GSH was used as a marker of tissue GSH. There were no baseline differences (age, ht, wt, %ideal wt, peak power, 30-s work capacity). Follow-up data on 18 subjects (9 Immunocal, 9 placebo) were analyzed. Both peak power [13 ± 3.5 (SE) %, P < 0.02] and 30-s work capacity (13 ± 3.7%, P < 0.03) increased significantly in the Immunocal group, with no change (2 ± 9.0 and 1 ± 9.3%) in the placebo group. Lymphocyte GSH also increased significantly in the Immunocal group (35.5 ± 11.04%, P < 0.02), with no change in the placebo group (−0.9 ± 9.6%). This is the first study to demonstrate that prolonged supplementation with a product designed to augment antioxidant defenses resulted in improved volitional performance.