bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of epinephrine on muscle glycogenolysis during exercise in trained men
Authors: Febbraio M. A. , Lambert D. L. , Starkie R. L. , Proietto J. , Hargreaves M.
Published: December 2017

Febbraio, M. A., D. L. Lambert, R. L. Starkie, J. Proietto, and M. Hargreaves. Effect of epinephrine on muscle glycogenolysis during exercise in trained men. J. Appl. Physiol. 84(2): 465–470, 1998.—To test the hypothesis that an elevation in circulating epinephrine increases intramuscular glycogen utilization, six endurance-trained men performed two 40-min cycling trials at 71 ± 2% of peak oxygen uptake in 20–22°C conditions. On the first occasion, subjects were infused with saline throughout exercise (Con). One week later, after determination of plasma epinephrine levels in Con, subjects performed the second trial (Epi) with an epinephrine infusion, which resulted in a twofold higher ( P < 0.01) plasma epinephrine concentration in Epi compared with Con. Although oxygen uptake was not different when the two trials were compared, respiratory exchange ratio was higher throughout exercise in Epi compared with Con (0.93 ± 0.01 vs. 0.89 ± 0.01; P < 0.05). Muscle glycogen concentration was not different when the trials were compared preexercise, but the postexercise value was lower ( P < 0.01) in Epi compared with Con. Thus net muscle glycogen utilization was greater during exercise with epinephrine infusion (224 ± 37 vs. 303 ± 30 mmol/kg for Con and Epi, respectively; P < 0.01). In addition, both muscle and plasma lactate and plasma glucose concentrations were higher ( P < 0.05) in Epi compared with Con. These data indicate that intramuscular glycogen utilization, glycolysis, and carbohydrate oxidation are augmented by elevated epinephrine during submaximal exercise in trained men.
Upper airway muscle activity and upper airway resistance in young adults during sleep
Authors: Henke Kathe G.
Published: December 2017

Henke, Kathe G. Upper airway muscle activity and upper airway resistance in young adults during sleep. J. Appl. Physiol. 84(2): 486–491, 1998.—To determine the relationship between upper airway muscle activity and upper airway resistance in nonsnoring and snoring young adults, 17 subjects were studied during sleep. Genioglossus and alae nasi electromyogram activity were recorded. Inspiratory and expiratory supraglottic resistance (Rinsp and Rexp, respectively) were measured at peak flow, and the coefficients of resistance ( K insp and K exp, respectively) were calculated. Data were recorded during control, with continuous positive airway pressure (CPAP), and on the breath immediately after termination of CPAP. Rinsp during control averaged 7 ± 1 and 10 ± 2 cmH2O ⋅ l−1 ⋅ s and K inspaveraged 26 ± 5 and 80 ± 27 cmH2O ⋅ l−1 ⋅ s−2in the nonsnorers and snorers, respectively ( P = not significant). On the breath immediately after CPAP, K insp did not increase over control in snorers (80 ± 27 for control vs. 46 ± 6 cmH2O ⋅ l−1 ⋅ s−2for the breath after CPAP) or nonsnorers (26 ± 5 vs. 29 ± 6 cmH2O ⋅ l−1 ⋅ s−2). These findings held true for Rinsp. K exp did not increase in either group on the breath immediately after termination of CPAP. Therefore, 1) increases in upper airway resistance do not occur, despite reductions in electromyogram activity in young snorers and nonsnorers, and 2) increases in Rexp and expiratory flow limitation are not observed in young snorers.
Normal forces and myofibrillar disruption after repeated eccentric exercise
Authors: Hortobágyi Tibor , Houmard Joseph , Fraser David , Dudek Ronald , Lambert Jean , Tracy James
Published: December 2017

Hortobágyi, Tibor, Joseph Houmard, David Fraser, Ronald Dudek, Jean Lambert, and James Tracy. Normal forces and myofibrillar disruption after repeated eccentric exercise. J. Appl. Physiol. 84(2): 492–498, 1998.—To investigate the “rapid-adaptation” phenomenon, we examined force, neural, and morphological adaptations in 12 subjects who performed 100 eccentric contractions with the quadriceps muscle ( bout 1) and repeated the same exercise after a 2-wk hiatus ( bout 2). Two days after bout 1, quadriceps muscle strength and surface electromyographic (EMG) activity declined ∼37 and 28%, respectively, in the control group ( n = 6). At day 2 after bout 1, significant increases occurred in patellar tendon reflex amplitude (∼25%), muscle soreness (fivefold), and serum creatine kinase (220%), and 65 ± 12% of the total number of pixels in the EMG indicated myofibrillar disruption. At day 7 after bout 1, all variables returned to normal. At day 2after bout 2, no significant changes occurred in force, EMG, creatine kinase, or soreness, but reflex amplitude increased, and 23 ± 4% of the total number of pixels in the EMG still indicated myofibrillar disruption. The results suggest that the rapid force recovery following eccentric exercise is mediated at least in part by neural factors and that this recovery may occur independently of cell disruption.
Selective stimulation of jugular ganglion afferent neurons in guinea pig airways by hypertonic saline
Authors: Pedersen Karen E. , Meeker Sonya N. , Riccio Margerita M. , Undem Bradley J.
Published: December 2017

Pedersen, Karen E., Sonya N. Meeker, Margerita M. Riccio, and Bradley J. Undem. Selective stimulation of jugular ganglion afferent neurons in guinea pig airways by hypertonic saline. J. Appl. Physiol. 84(2): 499–506, 1998.—We evaluated the ability of hyperosmolar stimuli to activate afferent nerves in the guinea pig trachea and main bronchi and investigated the neural pathways involved. By using electrophysiological techniques, studies in vitro examined the effect of hyperosmolar solutions of sodium chloride (hypertonic saline) on guinea pig airway afferent nerve endings arising from either vagal nodose or jugular ganglia. The data reveal a differential sensitivity of airway afferent neurons to activation with hypertonic saline. Afferent fibers (both Aδ and C fibers) with cell bodies located in jugular ganglia were much more sensitive to stimulation with hypertonic saline, compared with afferent neurons with cell bodies located in nodose ganglia. Additional studies in vivo demonstrated that inhalation of aerosols of hypertonic saline induced plasma extravasation in guinea pig trachea that was mediated via tachykinin NK1receptors. Identification of a differential sensitivity of guinea pig airway afferent nerves to hypertonic saline leads to the speculation that airway responses to hyperosmolar stimuli may result from activation of afferent neurons originating predominantly from the jugular ganglion.
Mechanical advantage of the canine triangularis sterni
Authors: De Troyer André , Legrand Alexandre
Published: December 2017

De Troyer, André, and Alexandre Legrand.Mechanical advantage of the canine triangularis sterni. J. Appl. Physiol. 84(2): 562–568, 1998.—Recent studies on the canine parasternal intercostal, sternomastoid, and scalene muscles have shown that the maximal changes in airway opening pressure (ΔPao) obtained per unit muscle mass (ΔPao/ m) during isolated contraction are closely related to the fractional changes in muscle length per unit volume increase of the relaxed chest wall. In the present study, we have examined the validity of this relationship for the triangularis sterni, an important expiratory muscle of the rib cage in dogs. Passive inflation above functional residual capacity (FRC) induced a virtually linear increase in muscle length, such that, with a 1.0-liter inflation, the muscle lengthened by 17.9 ± 1.6 (SE) % of its FRC length. When the muscle in one interspace was maximally stimulated at FRC, Pao increased by 0.84 ± 0.11 cmH2O. However, in agreement with the length-tension characteristics of the muscle, when lung volume was increased by 1.0 liter before stimulation, the rise in Pao amounted to 1.75 ± 0.12 cmH2O. At the higher volume, ΔPao/ m therefore averaged + 0.53 ± 0.05 cmH2O/g, such that the coefficient of proportionality between the change in triangularis sterni length during passive inflation and ΔPao/ mwas the same as that previously obtained for the parasternal intercostal and neck inspiratory muscles. These observations, therefore, confirm that there is a unique relationship between the fractional changes in length of the respiratory muscles, both inspiratory and expiratory, during passive inflation and their ΔPao/ m. Consequently, the maximal effect of a particular muscle on the lung can be predicted on the basis of its change in length during passive inflation and its mass. A geometric analysis of the rib cage also established that the lengthening of the canine triangularis sterni during passive inflation is much greater than the shortening of the parasternal intercostals because, in dogs, the costal cartilages slope downward from the sternum.
Effect of hypoxia on pulmonary blood flow-segmental vascular resistance relationship in perfused cat lungs
Authors: Toga Hirohisa , Okazaki Hiroshi , Ishigaki Masanobu , Noguchi Tetsuhiko , Huang Jyongsu , Fukunaga Toshiharu , Nagasaka Yukio , Takahashi Keiji , Ohya Nobuo
Published: December 2017

To investigate the effect of alveolar hypoxia on the pulmonary blood flow-segmental vascular resistance relationship, we determined the longitudinal distribution of vascular resistance while increasing blood flow during hyperoxia or hypoxia in perfused cat lungs. We measured microvascular pressures by the micropipette servo-null method, partitioned the pulmonary vessels into three segments [i.e., arterial (from main pulmonary artery to 30- to 50-μm arterioles), venous (from 30- to 50-μm venules to left atrium), and microvascular (between arterioles and venules) segments] and calculated segmental vascular resistance. During hyperoxia, total resistance decreased with increased blood flow because of a reduction of microvascular resistance. In contrast, during hypoxia, not only microvascular resistance but also arterial resistance decreased with increase of blood flow while venous resistance remained unchanged. The reduction of arterial resistance was presumably caused by arterial distension induced by an elevated arterial pressure during hypoxia. We conclude that, during hypoxia, both microvessels and arteries >50 μm in diameter play a role in preventing further increases in total pulmonary vascular resistance with increased blood flow.
Viral respiratory infection increases susceptibility of young rats to hypoxia-induced pulmonary edema
Authors: Carpenter Todd C. , Reeves John T. , Durmowicz Anthony G.
Published: December 2017

Recent clinical observations of a high incidence of preexisting respiratory infections in pediatric cases of high-altitude pulmonary edema prompted us to ask whether such infections would increase the susceptibility to hypoxia-induced pulmonary edema in young rats. We infected weanling rats with Sendai virus, thus causing a mild respiratory infection. Within 7 days of infection, Sendai virus was essentially undetectable by using viral culture and immunohistochemical techniques. Animals at day 7 of Sendai virus infection were then exposed to normobaric hypoxia (fraction of inspired O2= 0.1) for 24 h and examined for increases in gravimetric lung water and in vascular permeability, as well as for histological evidence of increased lung water. Bronchoalveolar lavage was performed on a separate series of animals. Compared with control groups, infected hypoxic animals showed significant increases in perivascular cuffing, gravimetric lung water, and lung protein leak. In addition, infected hypoxic animals had increases in lavage fluid cell counts and protein content compared with controls. We conclude that young rats, exposed to moderate hypoxia while recovering from a mild viral respiratory infection, may demonstrate evidence of early pulmonary edema formation, a finding of potential relevance to human high-altitude pulmonary edema.
Effect of upper airway negative pressure on inspiratory drive during sleep
Authors: Eastwood P. R. , Curran A. K. , Smith C. A. , Dempsey J. A.
Published: December 2017

To determine the effect of upper airway (UA) negative pressure and collapse during inspiration on regulation of breathing, we studied four unanesthetized female dogs during wakefulness and sleep while they breathed via a fenestrated tracheostomy tube, which was sealed around the permanent tracheal stoma. The snout was sealed with an airtight mask, thereby isolating the UA when the fenestration (Fen) was closed and exposing the UA to intrathoracic pressure changes, but not to flow changes, when Fen was open. During tracheal occlusion with Fen closed, inspiratory time (Ti) increased during wakefulness, non-rapid-eye-movement (NREM) sleep and rapid-eye-movement (REM) sleep (155 ± 8, 164 ± 11, and 161 ± 32%, respectively), reflecting the removal of inhibitory lung inflation reflexes. During tracheal occlusion with Fen open (vs. Fen closed): 1) the UA remained patent; 2) Ti further increased during wakefulness and NREM (215 ± 52 and 197 ± 28%, respectively) but nonsignificantly during REM sleep (196 ± 42%); 3) mean rate of rise of diaphragm EMG (EMGdi/Ti) and rate of fall of tracheal pressure (Ptr/Ti) were decreased, reflecting an additional inhibitory input from UA receptors; and 4) both EMGdi/Ti and Ptr/Ti were decreased proportionately more as inspiration proceeded, suggesting greater reflex inhibition later in the effort. Similar inhibitory effects of exposing the UA to negative pressure (via an open tracheal Fen) were seen when an inspiratory resistive load was applied over several breaths during wakefulness and sleep. These inhibitory effects persisted even in the face of rising chemical stimuli. This inhibition of inspiratory motor output is alinear within an inspiration and reflects the activation of UA pressure-sensitive receptors by UA distortion, with greater distortion possibly occurring later in the effort.
Distribution of coronary arterial capacitance in a canine model
Authors: Lader Alan S. , Smith Rebecca S. , Phillips George C. , McNamee James E. , Abel Francis L.
Published: December 2017

The capacitative properties of the major left coronary arteries, left main (LM), left anterior descending (LAD), and left circumflex (LCX), were studied in 19 open-chest isolated dog hearts. Capacitance was determined by using ramp perfusion and a left ventricular-to-coronary shunt diastolic decay method; both methods gave similar results, indicating a minimal systolic capacitative component. Increased pericardial pressure (PCP), 25 mmHg, was used to experimentally alter transmural wall pressure. The response to increased PCP was different in the LAD vs. LCX; increasing PCP decreased capacitance in the LCX but increased capacitance in the LAD. This may have been due to the different intramural vs. epicardial volume distribution of these vessels and a decrease in intramural tension during increased PCP. Increased PCP decreased LCX capacitance by ∼13%, but no changes in conductance or zero flow pressure intercept occurred in any of the three vessels, i.e., evidence against the waterfall theory of vascular collapse at these levels of PCP. Coronary arterial capacitance was also linearly related to perfusion pressure.
Modeling developmental changes in strength and aerobic power in children
Authors: Nevill Alan M. , Holder Roger L. , Baxter-Jones Adam , Round Joan M. , Jones David A.
Published: December 2017

The present study examined two contrasting multilevel model structures to describe the developmental (longitudinal) changes in strength and aerobic power in children: 1) an additive polynomial structure and 2) a multiplicative structure with allometric body size components. On the basis of the maximum log-likelihood criterion, the multiplicative “allometric” model was shown to be superior to the additive polynomial model when fitted to the data from two published longitudinal studies and to provide more plausible solutions within and beyond the range of observations.The multilevel regression analysis of study 1 confirmed that aerobic power develops approximately in proportion to body mass, m1/3. The analyses from study 2 identified a significant increase in quadriceps and biceps strength, in proportion to body size, plus an additional contribution from age, centered at about peak height velocity (PHV). The positive “age” term for boys suggested that at PHV the boys were becoming stronger in the quadriceps and biceps in relation to their body size. In contrast, the girls’ age term was either negligible (quadriceps) or negative (biceps), indicating that at PHV the girls’ strength was developing in proportion to or, in the case of the biceps, was becoming weaker in relation to their body size.
Central interaction between carotid baroreceptors and skeletal muscle receptors inhibits sympathoexcitation
Authors: Potts Jeffrey T. , Hand Gregory A. , Li Jianhua , Mitchell Jere H.
Published: December 2017

To determine the potential of an inhibitory interaction between the carotid sinus baroreflex (CSB) and the exercise pressor reflex (EPR), both pathways were activated to produce sympathoexcitation. It was hypothesized that, under conditions when the baroreflex increased sympathetic outflow, the interaction between CSB and EPR would be inhibitory. Bilateral carotid occlusion (BCO), electrically induced muscle contraction (EMC), and passive muscle stretch (PMS) were used to evoke sympathoexcitation. BCO decreased sinus pressure 50 ± 5 mmHg, and the levels of muscle tension generated by EMC and PMS were 7 ± 2 and 8 ± 1 kg, respectively. This resulted in significant increases in mean arterial pressure (MAP) of 55 ± 9, 50 ± 7, and 50 ± 6 mmHg ( P = not significant, BCO vs. EMC vs. PMS) and in heart rate (HR) of 7 ± 2, 19 ± 4, and 17 ± 2 beats/min ( P < 0.05, BCO vs. EMC and PMS). When BCO was combined with EMC or PMS, the reflex increase in MAP was augmented (80 ± 8 and 79 ± 10 mmHg; BCO+EMC and BCO+PMS, respectively; P< 0.05). However, summation of the individual MAP responses was greater than the response evoked during coactivation (106 ± 11 and 103 ± 12 mmHg, respectively, P < 0.05). Because summing the individual blood pressure responses exceeded the response during coactivation, the net effect was that the CSB and EPR interacted in an occlusive manner. In contrast, summation of the individual chronotropic responses was the same as the response evoked during coactivation. Moreover, there was no difference in summation of the individual MAP or HR responses when muscle afferents were activated by either EMC or PMS. In conclusion, the interaction between the CSB and the EPR in control of MAP was occlusive when both reflexes were stimulated to evoke sympathoexcitation. However, summation of the reflex changes in HR was simply additive.
Polycythemic responses to hypoxia: molecular and genetic mechanisms of chronic mountain sickness
Authors: Ou L. C. , Salceda S. , Schuster S. J. , Dunnack L. M. , Brink-Johnsen T. , Chen J. , Leiter J. C.
Published: December 2017

We examined erythropoietin (EPO) gene expression and EPO production during hypoxia in two Sprague-Dawley rat strains with divergent polycythemic responses to hypoxia. Hilltop (H) rats develop severe polycythemia, severe hypoxemia, and pulmonary artery hypertension. The H rats often die from a syndrome indistinguishable from chronic mountain sickness (CMS) in humans. Madison (M) rats develop polycythemia and pulmonary artery hypertension that is modest and suffer no excess mortality. We tested the hypothesis that these rat strains have different stimulus-response characteristics governing EPO production. Rats of each strain were exposed to hypoxia (0.5 atm, 73 Torr inspired [Formula: see text]), and renal tissue EPO mRNA and EPO levels, plasma EPO, ventilation, arterial and renal venous blood gases, and indexes of renal function were measured at fixed times during a 30-day hypoxic exposure. During extended hypoxic exposure, H rats had significantly elevated renal EPO mRNA, renal EPO, and plasma EPO levels compared with M rats. Ventilatory responses and indexes of renal function were similar in the strains during the hypoxic exposure. H rats had greater arterial hypoxemia from the onset of hypoxia and more severe renal tissue hypoxemia and greater polycythemia after 14 days of hypoxic exposure. When EPO responses were expressed as functions of renal venous[Formula: see text], the two strains appeared to lie on the same dose-response curves, but the responses of H rats were shifted along the curve toward more hypoxic values. We conclude that H rats have significantly greater polycythemia secondary to poorer renal tissue oxygenation, but the stimulus-response characteristics governing EPO gene expression and EPO production do not seem to differ between M and H rats. Finally, the regulation of EPO levels during hypoxia occurs primarily at the transcriptional level.
Isotonic contractile and fatigue properties of developing rat diaphragm muscle
Authors: Zhan Wen-Zhi , Watchko Jon F. , Prakash Y. S. , Sieck Gary C.
Published: December 2017

Postnatal transitions in myosin heavy chain (MHC) isoform expression were found to be associated with changes in both isometric and isotonic contractile properties of rat diaphragm muscle (Diam). Expression of MHCneopredominated in neonatal Diamfibers but was usually coexpressed with MHCslowor MHC2Aisoforms. Expression of MHCneodisappeared by day 28. Expression of MHC2Xand MHC2Bemerged at day 14 and increased thereafter. Associated with these MHC transitions in the Diam, maximum isometric tetanic force (Po), maximum shortening velocity, and maximum power output progressively increased during early postnatal development. Maximum power output of the Diamoccurred at ∼40% Poat days 0 and 7 and at ∼30% Poin older animals. Susceptibility to isometric and isotonic fatigue, defined as a decline in force and power output during repetitive activation, respectively, increased with maturation. Isotonic endurance time, defined as the time for maximum power output to decline to zero, progressively decreased with maturation. In contrast, isometric endurance time, defined as the time for force to decline to 30–40% Po, remained >300 s until after day 28. We speculate that with the postnatal transition to MHC2Xand MHC2Bexpression energy requirements for contraction increase, especially during isotonic shortening, leading to a greater imbalance between energy supply and demand.
Effects of HCl-pepsin laryngeal instillations on upper airway patency-maintaining mechanisms
Authors: Sant’Ambrogio Franca B. , Sant’Ambrogio Giuseppe , Chung Kyungsoon
Published: December 2017

Gastroesophageal reflux has been indicated as an etiopathological factor in disorders of the upper airway. Upper airway collapsing pressure stimulates pressure-responsive laryngeal receptors that reflexly increase the activity of upper airway abductor muscles. We studied, in anesthetized dogs, the effects of repeated laryngeal instillations of HCl-pepsin (HCl-P; pH = 2) on the response of laryngeal afferent endings and the posterior cricoarytenoid muscle (PCA) to negative pressure. The effect of negative pressure on receptor discharge or PCA activity was evaluated by comparing their response to upper airway (UAO) and tracheal occlusions (TO). It is only during UAO, but not during TO, that the larynx is subjected to negative transmural pressure. HCl-P instillation decreased the rate of discharge during UAO of the 10 laryngeal receptors studied from 56.4 ± 10.9 (SE) to 38.2 ± 9.2 impulses/s ( P < 0.05). With UAO, the peak PCA moving time average, normalized by dividing it by the peak values of esophageal pressure, decreased after six HCl-P trials from 4.29 ± 0.31 to 2.23 ± 0.18 ( n = 6; P < 0.05). The responses to TO of either receptors or PCA remained unaltered. We conclude that exposure of the laryngeal mucosa to HCl-P solutions, as it may occur with gastroesophageal reflux, impairs the patency-maintaining mechanisms provided by laryngeal sensory feedback. Inflammatory and necrotic alterations of the laryngeal mucosa are likely responsible for these effects.
Age alters the cardiovascular response to direct passive heating
Authors: Minson Christopher T. , Wladkowski Stacey L. , Cardell Anthony F. , Pawelczyk James A. , Kenney W. Larry
Published: December 2017

During direct passive heating in young men, a dramatic increase in skin blood flow is achieved by a rise in cardiac output (Q˙c) and redistribution of flow from the splanchnic and renal vascular beds. To examine the effect of age on these responses, seven young (Y; 23 ± 1 yr) and seven older (O; 70 ± 3 yr) men were passively heated with water-perfused suits to their individual limit of thermal tolerance. Measurements included heart rate (HR),Q˙c(by acetylene rebreathing), central venous pressure (via peripherally inserted central catheter), blood pressures (by brachial auscultation), skin blood flow (from increases in forearm blood flow by venous occlusion plethysmography), splanchnic blood flow (by indocyanine green clearance), renal blood flow (by p-aminohippurate clearance), and esophageal and mean skin temperatures.Q˙cwas significantly lower in the older than in the young men (11.1 ± 0.7 and 7.4 ± 0.2 l/min in Y and O, respectively, at the limit of thermal tolerance; P < 0.05), despite similar increases in esophageal and mean skin temperatures and time to reach the limit of thermal tolerance. A lower stroke volume (99 ± 7 and 68 ± 4 ml/beat in Y and O, respectively, P < 0.05), most likely due to an attenuated increase in inotropic function during heating, was the primary factor for the lowerQ˙cobserved in the older men. Increases in HR were similar in the young and older men; however, when expressed as a percentage of maximal HR, the older men relied on a greater proportion of their chronotropic reserve to obtain the same HR response (62 ± 3 and 75 ± 4% maximal HR in Y and O, respectively, P < 0.05). Furthermore, the older men redistributed less blood flow from the combined splanchnic and renal circulations at the limit of thermal tolerance (960 ± 80 and 720 ± 100 ml/min in Y and O, respectively, P < 0.05). As a result of these combined attenuated responses, the older men had a significantly lower increase in total blood flow directed to the skin.
Myogenin, MyoD, and myosin expression after pharmacologically and surgically induced hypertrophy
Authors: Mozdziak P. E. , Greaser M. L. , Schultz E.
Published: December 2017

The relationship between myogenin or MyoD expression and hypertrophy of the rat soleus produced either by clenbuterol and 3,3′,5-triiodo-l-thyronine (CT) treatment or by surgical overload was examined. Mature female rats were subjected to surgical overload of the right soleus with the left soleus serving as a control. Another group received the same surgical treatment but were administered CT. Soleus muscles were harvested 4 wk after surgical overload and weighed. Myosin heavy chain isoforms were separated by using polyacrylamide gel electrophoresis while myogenin and MyoD expression were evaluated by Northern analysis. CT and functional overload increased soleus muscle weight. CT treatment induced the appearance of the fast type IIX myosin heavy chain isoform, depressed myogenin expression, and induced MyoD expression. However, functional overload did not alter myogenin or MyoD expression in CT-treated or non-CT-treated rats. Thus pharmacologically and surgically induced hypertrophy have differing effects on myogenin and MyoD expression, because their levels were associated with changes in myosin heavy chain composition (especially type IIX) rather than changes in muscle mass.
Role of extracellular [Ca2+] in fatigue of isolated mammalian skeletal muscle
Authors: Cairns Simeon P. , Hing Wayne A. , Slack John R. , Mills Roland G. , Loiselle Denis S.
Published: December 2017

The possible role of altered extracellular Ca2+concentration ([Ca2+]o) in skeletal muscle fatigue was tested on isolated slow-twitch soleus and fast-twitch extensor digitorum longus muscles of the mouse. The following findings were made. 1) A change from the control solution (1.3 mM [Ca2+]o) to 10 mM [Ca2+]o, or to nominally Ca2+-free solutions, had little effect on tetanic force in nonfatigued muscle. 2) Almost complete restoration of tetanic force was induced by 10 mM [Ca2+]oin severely K+-depressed muscle (extracellular K+ concentration of 10–12 mM). This effect was attributed to a 5-mV reversal of the K+-induced depolarization and subsequent restoration of ability to generate action potentials (inferred by using the twitch force-stimulation strength relationship). 3) Tetanic force depressed by lowered extracellular Na+concentration (40 mM) was further reduced with 10 mM [Ca2+]o. 4) Tetanic force loss at elevated extracellular K+ concentration (8 mM) and lowered extracellular Na+concentration (100 mM) was partially reversed with 10 mM [Ca2+]oor markedly exacerbated with low [Ca2+]o. 5) Fatigue induced by using repeated tetani in soleus was attenuated at 10 mM [Ca2+]o(due to increased resting and evoked forces) and exacerbated at low [Ca2+]o. These combined results suggest, first, that raised [Ca2+]oprotects against fatigue rather than inducing it and, second, that a considerable depletion of [Ca2+]oin the transverse tubules may contribute to fatigue.
Prolonged exposure to halothane and associated changes in carbohydrate metabolism in rat muscles in vivo
Authors: Ferreira Luis D. M. C.-B. , Palmer T. Norman , Fournier Paul A.
Published: December 2017

Halothane, an anesthetic presently used in animal experimentation, is reported to stimulate glycogen breakdown in isolated preparations of rat skeletal muscles, suggesting that it may not be a suitable anesthetic for the study of glycogen metabolism in rats in vivo. The purpose of this study was to establish whether prolonged exposure to halothane in rats in vivo is associated with accelerated glycogenolysis. Exposure of rats to halothane for up to 1 h was not accompanied by either any change in the levels of glycogen or increase in activity ratios of glycogen phosphorylase in muscles, irrespective of their fiber compositions. In marked contrast, the levels of lactate, inorganic phosphate, glucose 1-phosphate, glucose 6-phosphate, fructose 1,6-bisphosphate, and fructose 2,6-bisphosphate changed progressively during anesthesia. Accordingly, the interpretation of muscle metabolite levels must be performed with caution in experiments involving prolonged exposure to halothane. Overall, our findings indicate that the reported halothane-mediated stimulation of glycogen breakdown in vitro is likely to be an artifact and that halothane is a suitable anesthetic for experiments concerned with glycogen metabolism in rats.
Pulmonary blood flow distribution during partial liquid ventilation
Authors: Doctor Allan , Ibla Juan C. , Grenier Barry M. , Zurakowski David , Ferretti Michelle L. , Thompson John E. , Lillehei Craig W. , Arnold John H.
Published: December 2017

Regional pulmonary blood flow was investigated with radiolabeled microspheres in four supine lambs during the transition from conventional mechanical ventilation (CMV) to partial liquid ventilation (PLV) and with incremental dosing of perfluorocarbon liquid to a cumulative dose of 30 ml/kg. Four lambs supported with CMV served as controls. Formalin-fixed, air-dried lungs were sectioned according to a grid; activity was quantitated with a multichannel scintillation counter, corrected for weight, and normalized to mean flow. During CMV, flow in apical and hilar regions favored dependent lung ( P < 0.001), with no gradient across transverse planes from apex to diaphragm. During PLV the gradient within transverse planes found during CMV reversed, most notably in the hilar region, favoring nondependent lung ( P = 0.03). Also during PLV, flow was profoundly reduced near the diaphragm ( P < 0.001), and across transverse planes from apex to diaphragm a dose-augmented flow gradient developed favoring apical lung ( P < 0.01). We conclude that regional flow patterns during PLV partially reverse those noted during CMV and vary dramatically within the lung from apex to diaphragm.
Effect of hypohydration on gastric emptying and intestinal absorption during exercise
Authors: Ryan A. J. , Lambert G. P. , Shi X. , Chang R. T. , Summers R. W. , Gisolfi C. V.
Published: December 2017

Dehydration and hyperthermia may impair gastric emptying (GE) during exercise; the effect of these alterations on intestinal water flux (WF) is unknown. Thus the purpose of this study was to determine the effect of hypohydration (∼2.7% body weight) on GE and WF of a water placebo (WP) during cycling exercise (85 min, 65% maximal oxygen uptake) in a cool environment (22°C) and to also compare GE and WF of three carbohydrate-electrolyte solutions (CES) while the subjects were hypohydrated. GE and WF were determined simultaneously by a nasogastric tube placed in the gastric antrum and via a multilumen tube that spanned the duodenum and the first 25 cm of jejunum. Hypohydration was attained 12–16 h before experiments by low-intensity exercise in a hot (45°C), humid (relative humidity 50%) environment. Seven healthy subjects (age 26.7 ± 1.7 yr, maximal oxygen uptake 55.9 ± 8.2 ml ⋅ kg−1⋅ min−1) ingested either WP or a 6% (330 mosmol), 8% (400 mosmol), or a 9% (590 mosmol) CES the morning following hypohydration. For comparison, subjects ingested WP after a euhydration protocol. Solutions (∼2.0 liters total) were ingested as a large bolus (4.6 ml/kg body wt) 5 min before exercise and as small serial feedings (2.3 ml/kg body wt) every 10 min of exercise. Average GE rates were not different among conditions ( P > 0.05). Mean (±SE) values for WF were also similar ( P > 0.05) for the euhydration (15.3 ± 1.7 ml ⋅ cm−1⋅ h−1) and hypohydration (18.3 ± 2.6 ml ⋅ cm−1⋅ h−1) experiments. During exercise after hypohydration, water absorption was greater ( P < 0.05) with ingestion of WP (18.3 ± 2.6) and the 6% CES (16.5 ± 3.7), compared with the 8% CES (6.9 ± 1.5) and the 9% CES (1.8 ± 1.7). Mean values for final core temperature (38.6 ± 0.1°C), heart rate (152 ± 1 beats/min), and change in plasma volume (−5.7 ± 0.7%) were similar among experimental trials. We conclude that 1) hypohydration to ∼3% body weight does not impair GE or fluid absorption during moderate exercise when ingesting WP, and 2) hyperosmolality (>400 mosmol) reduced WF in the proximal intestine.
Effects of hepatic portal infusion of deionized water on metabolic and hormonal responses to exercise in rats
Authors: Latour Martin G. , Désy François , Warren Claude , Lavoie Jean-Marc
Published: December 2017

The present study was conducted to investigate the in vivo effects of an intrahepatic infusion of deionized water during exercise in rats. Adrenodemedullated male Sprague-Dawley rats were continuously infused for 30 min either at rest or during treadmill exercise (26 m/min, 0% grade). Rats were randomly assigned to one of three infusion conditions (52 μl/min) with either deionized water (PW) or saline (PS; NaCl; 0.9%) via the hepatic portal vein or deionized water through the jugular vein (JW). The exercise period caused a significant ( P < 0.05) decrease in liver glycogen and relative liver water content and peripheral and portal blood glucose and insulin while increasing peripheral and portal glucagon and K+ plasma concentrations. These responses, with the exception of K+, were not influenced by the different types of infusions. The increase in K+ during exercise was significantly ( P < 0.05) higher in JW rats than in the PW and PS groups. Both the infusion and exercise protocols did not significantly alter the liver weight-to-body weight ratio, plasma osmolality, free fatty acids, β-hydroxybutyrate, Na+, Cl−, vasopressin, and catecholamine concentrations. It is concluded that an hepatic portal infusion of deionized water does not specifically alter the metabolic and hormonal responses to exercise in rats.
Localized infusion of IGF-I results in skeletal muscle hypertrophy in rats
Authors: Adams Gregory R. , McCue Samuel A.
Published: December 2017

Insulin-like growth factor I (IGF-I) peptide levels have been shown to increase in overloaded skeletal muscles (G. R. Adams and F. Haddad. J. Appl. Physiol. 81: 2509–2516, 1996). In that study, the increase in IGF-I was found to precede measurable increases in muscle protein and was correlated with an increase in muscle DNA content. The present study was undertaken to test the hypothesis that direct IGF-I infusion would result in an increase in muscle DNA as well as in various measurements of muscle size. Either 0.9% saline or nonsystemic doses of IGF-I were infused directly into a non-weight-bearing muscle of rats, the tibialis anterior (TA), via a fenestrated catheter attached to a subcutaneous miniosmotic pump. Saline infusion had no effect on the mass, protein content, or DNA content of TA muscles. Local IGF-I infusion had no effect on body or heart weight. The absolute weight of the infused TA muscles was ∼9% greater ( P < 0.05) than that of the contralateral TA muscles. IGF-I infusion resulted in significant increases in the total protein and DNA content of TA muscles ( P < 0.05). As a result of these coordinated changes, the DNA-to-protein ratio of the hypertrophied TA was similar to that of the contralateral muscles. These results suggest that IGF-I may be acting to directly stimulate processes such as protein synthesis and satellite cell proliferation, which result in skeletal muscle hypertrophy.
Analytic assessment of the various bioimpedance methods used to estimate body water
Authors: Matthie J. , Zarowitz B. , De Lorenzo A. , Andreoli A. , Katzarski K. , Pan G. , Withers P.
Published: December 2017

Knowledge of patient fluid distribution would be useful clinically. Both single-frequency (SF) and impedance modeling approaches are proposed. The high intercorrelation between body water compartments makes determining the best approach difficult. This study was conducted to evaluate the merits of an SF approach. Mathematical simulation was performed to determine the effect of tissue change on resistance and reactance. Dilution results were reanalyzed, and resistance and parallel reactance were used to predict the intracellular water for two groups. Results indicated that the amount of intracellular and extracellular water conduction at any SF can vary with tissue change, and reactance at any SF is affected by all tissue parameters. Modeling provided a good prediction of dilution intracellular and extracellular water, but an SF method did not. Intracellular, extracellular, and total body water were equally predicted at all frequencies by SF resistance and parallel reactance. Extracellular and intracellular water are best measured through modeling, because only at the zero and infinite frequencies are the results sensitive only to extracellular and intracellular water. At all other frequencies there are other effects.
Hypohydration effects on skeletal muscle performance and metabolism: a 31P-MRS study
Authors: Montain Scott J. , Smith Sinclair A. , Mattot Ralph P. , Zientara Gary P. , Jolesz Ferenc A. , Sawka Michael N.
Published: December 2017

The purpose of this study was to determine whether hypohydration reduces skeletal muscle endurance and whether increased H+ and Pi might contribute to performance degradation. Ten physically active volunteers (age 21–40 yr) performed supine single-leg, knee-extension exercise to exhaustion in a 1.5-T whole body magnetic resonance spectroscopy (MRS) system when euhydrated and when hypohydrated (4% body wt).31P spectra were collected at a rate of one per second at rest, exercise, and recovery, and were grouped and averaged to represent 10-s intervals. The desired hydration level was achieved by having the subjects perform 2–3 h of exercise in a warm room (40°C dry bulb, 20% relative humidity) with or without fluid replacement 3–8 h before the experiment. Time to fatigue was reduced ( P < 0.05) by 15% when the subjects were hypohydrated [213 ± 12 vs. 251 ± 15 (SE) s]. Muscle strength was generally not affected by hypohydration. Muscle pH and Pi/β-ATP ratio were similar during exercise and at exhaustion, regardless of hydration state. The time constants for phosphocreatine recovery were also similar between trials. In summary, moderate hypohydration reduces muscle endurance, and neither H+ nor Pi concentration appears to be related to these reductions.
l-NAME does not affect exercise-induced pulmonary hypertension in Thoroughbred horses
Authors: Manohar Murli , Goetz Thomas E.
Published: December 2017

The present study was carried out to examine the effects of nitric oxide synthase inhibition with Nω-nitro-l-arginine methyl ester (l-NAME) on the right atrial as well as on the pulmonary arterial, capillary, and venous blood pressures of horses during rest and exercise performed at maximal heart rate (HRmax). Experiments were carried out on seven healthy, sound, exercise-trained Thoroughbred horses. Using catheter-tip manometers, with signals referenced at the point of the shoulder, we determined phasic and mean right atrial and pulmonary vascular pressures in two sets of experiments [control (no medications) and l-NAME (20 mg/kg iv given 10 min before exercise studies)]. The studies were carried out in random order 7 days apart. Measurements were made at rest and during treadmill exercise performed on a 5% uphill grade at 6, 8, and 14.2 m/s. Exercise on a 5% uphill grade at 14.2 m/s elicited HRmaxand could not be sustained for >90 s. In quietly standing horses,l-NAME administration caused a significant rise in right atrial, as well as pulmonary arterial, capillary, and venous pressures. This indicates that nitric oxide synthase inhibition modifies the basal pulmonary vasomotor tone. In both treatments, exercise caused progressive significant increments in right atrial and pulmonary vascular pressures, but the values recorded in the l-NAME study were not different from those in the control study. The extent of exercise-induced tachycardia was significantly decreased in thel-NAME study at 6 and 8 m/s but not at 14.2 m/s. Thus, l-NAME administration may not modify the equine pulmonary vascular tone during exercise at HRmax. However, as indicated by a significant reduction in heart rate,l-NAME seems to modify the sympathoneurohumoral response to submaximal exercise.
Influence of carbohydrate status on immune responses before and after endurance exercise
Authors: Mitchell J. B. , Pizza F. X. , Paquet A. , Davis B. J. , Forrest M. B. , Braun W. A.
Published: December 2017

To determine the effect of carbohydrate (CHO) status on immune responses after long-duration exercise, on two occasions, 10 men completed a glycogen-depleting bout of cycle ergometry followed by 48 h of either a high-CHO diet (HiCHO; 8.0 g CHO/kg) or a low-CHO diet (LoCHO; 0.5 g CHO/kg). After the 48 h, subjects completed a 60-min ride at 75% maximal O2 uptake (EX). Blood samples were taken predepletion, pre-EX, post-EX, and 2 and 24 h post-EX and were assayed for leukocyte number and function, glucose, glutamine, and cortisol. The glucose responses were significantly higher in the HiCHO (4.62 ± 0.26 mM) vs. the LoCHO (3.19 ± 0.15 mM) condition post-EX, and glutamine was significantly higher in the HiCHO (0.472 ± 0.036 mM) vs. the LoCHO (0.410 ± 0.025 mM) condition throughout. Cortisol levels were significantly greater in the LoCHO (587 ± 50 nM) vs. the HiCHO (515 ± 62 nM) condition throughout the trial. Lymphocyte proliferation (phytohemagglutinin) was significantly depressed after exercise. However, there was no difference between conditions, and the depression was not correlated with elevations in cortisol. Circulating numbers of leukocytes, neutrophils, lymphocytes, and lymphocyte subsets were significantly greater in the LoCHO vs. the HiCHO condition at the post-EX and 2 h post-EX time points. These data indicate that the exercise and diet manipulation altered the number of circulating leukocytes but did not affect the decrease in lymphocyte proliferation that occurred after exercise.
Redistribution of pulmonary blood flow during unilateral hypoxia in prone and supine dogs
Authors: Mann Christopher M. , Domino Karen B. , Walther Sten M. , Glenny Robb W. , Polissar Nayak L. , Hlastala Michael P.
Published: December 2017

We used fluorescent-labeled microspheres in pentobarbital-anesthetized dogs to study the effects of unilateral alveolar hypoxia on the pulmonary blood flow distribution. The left lung was ventilated with inspired O2 fraction of 1.0, 0.09, or 0.03 in random order; the right lung was ventilated with inspired O2 fraction of 1.0. The lungs were removed, cleared of blood, dried at total lung capacity, then cubed to obtain ∼1,500 small pieces of lung (∼1.7 cm3). The coefficient of variation of flow increased ( P < 0.001) in the hypoxic lung but was unchanged in the hyperoxic lung. Most (70–80%) variance in flow in the hyperoxic lung was attributable to structure, in contrast to only 30–40% of the variance in flow in the hypoxic lung ( P < 0.001). When adjusted for the change in total flow to each lung, 90–95% of the variance in the hyperoxic lung was attributable to structure compared with 70–80% in the hypoxic lung ( P < 0.001). The hilar-to-peripheral gradient, adjusted for change in total flow, decreased in the hypoxic lung ( P = 0.005) but did not change in the hyperoxic lung. We conclude that hypoxic vasoconstriction alters the regional distribution of flow in the hypoxic, but not in the hyperoxic, lung.
Effects of isometric training on skeletal myosin heavy chain expression
Authors: Haddad Fadia , Qin Anqi X. , Zeng Ming , McCue Sam A. , Baldwin Kenneth M.
Published: December 2017

This study tested the hypothesis that an isometric resistance-training program induces upregulation of slow myosin heavy chain (MHC) expression in a fast-twitch skeletal muscle. Thus we studied the effects of two resistance-training programs on rodent medial gastrocnemius (MG) muscle that were designed to elicit repetitive isometric contractions (10–12 per set; 4 sets per session) of different duration (8 vs. 5 s) and activation frequency (100 vs. 60 Hz) per contraction during each training session (total of 6 and 12 sessions). Results showed that both training paradigms produced significant increases in muscle weight (∼11–13%) after completion of training ( P < 0.05). Significant transformations in MHC expression occurred and involved specifically a decrease in the relative expression of the fast type IIb MHC and concomitant increased expression of the fast type IIx MHC. These adaptations were observed in both the “white” and “red” regions of the MG, and they occurred at both the mRNA and protein levels. These adaptations were detected after only six training sessions. Neither of the training programs produced any change in the relative expression of either the slow type I MHC or the moderately fast type IIa MHC, which can be upregulated in the red MG by chronic functional overload. These findings show that the isometric protocols used in this investigation were not sufficient to induce the hypothesized changes in the myosin heavy chain isoform expression in rodent skeletal muscle.