bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of growth hormone on diaphragmatic recovery from malnutrition
Authors: Lanz J. K. , Donahoe M. , Rogers R. M. , Ontell M.
Published: December 2017

A 25% weight loss was induced in adult Fisher 344 rats by nutritional deprivation. Subsequently, normal feeding was resumed. Refed animals were divided into three groups and received recombinant human growth hormone (rhGH) injections during 5 wk of refeeding, saline injections during 5 wk of refeeding, or 9 wk of refeeding without injections. The effects of nutritional deprivation and the various refeeding protocols on the cross-sectional areas (CSA) of each of the four types of myofibers [typed immunohistochemically with antibodies against four myosin heavy chain (MHC) isoforms known to be present in the rat diaphragm] were determined. Malnutrition decreased the CSA of myofibers containing MHC2X, MHC2B, and MHC2A (i.e., fast myofibers), with the greatest effect on muscle mass being due to the atrophy of fibers containing MHC2X. Fibers containing MHC beta/slow failed to undergo malnutrition-induced atrophy. Whereas refeeding for 5 wk in the absence of rhGH allowed the recovery of CSA of fibers containing MHC2A, fibers containing MHC2B and MHC2X remained smaller than fibers of similar type in control animals. In contrast, 5 wk of refeeding supplemented with rhGH returned all fiber CSAs to control values. Even when refeeding alone was extended to 9 wk to allow for weight stabilization, the CSA of the fibers containing MHC2B and MHC2X remained smaller than similar fibers in control muscle. Serum insulin-like growth factor, a marker of malnutrition (R. Reeves and J. Elders, J. Nutr. 109: 613–620, 1979), was significantly decreased after nutritional deprivation and returned to normal after 5 wk of refeeding and GH supplementation.
Vasopressin inhibits diuresis induced by water immersion in humans
Authors: Farrow S. , Banta G. , Schallhorn S. , May R. , Mers A. , Cadaret L. , Rydstedt L. , Lockette W.
Published: December 2017

We tested the hypothesis that 1-desamino-8-D-arginine vasopressin (DDAVP), a V2-receptor agonist, could inhibit the diuresis induced by water immersion in humans. Water and electrolyte excretion, plasma atrial natriuretic factor concentration, and plasma aldosterone concentration were measured initially and after 3 h of water immersion in 13 healthy sodium-replete men given either placebo or 20 micrograms of intranasal DDAVP. Guanosine 3′,5′-cyclic monophosphate and urea excretion and urine osmolality were also determined. DDAVP inhibited the diuresis induced by water immersion in men: 758 +/- 168 (SE) ml/3 h in the placebo group vs. 159 +/- 28 ml/3 h in the DDAVP group (P less than 0.05). After 3 h of water immersion, plasma atrial natriuretic factor concentrations were increased from 11 +/- 2 to 20 +/- 4 pg/ml in the placebo group and from 14 +/- 2 to 33 +/- 4 pg/ml in the DDAVP group (P less than 0.05). Plasma aldosterone concentrations were decreased from 98 +/- 18 to 45 +/- 6 pg/ml in the placebo group (P less than 0.05) and from 54 +/- 17 to 25 +/- 5 pg/ml in the DDAVP group (P less than 0.05). Despite these changes in aldosterone and atrial natriuretic factor concentrations, which should increase sodium excretion, DDAVP decreased the natriuresis induced by water immersion in humans: 56 +/- 8 meq Na+/3 h in the placebo group vs. 36 +/- 6 meq Na+/3 h in the DDAVP group (P less than 0.05). DDAVP may be used to prevent the diuresis associated with central redistribution of blood volumes that occur during water immersion.(ABSTRACT TRUNCATED AT 250 WORDS)
Muscle damage is not a function of muscle force but active muscle strain
Authors: Lieber R. L. , Friden J.
Published: December 2017

Contractile properties of rabbit tibialis anterior muscles were measured after eccentric contraction to investigate the mechanism of muscle injury. In the first experiment, two groups of muscles were strained 25% of the muscle fiber length at identical rates. However, because the timing of the imposed length change relative to muscle activation was different, the groups experienced dramatically different muscle forces. Because muscle maximum tetanic tension and other contractile parameters measured after 30 min of cyclic activity with either strain timing pattern were identical (P > 0.4), we concluded that muscle damage was equivalent despite very different imposed forces. This result was supported by a second experiment in which the same protocol was performed at one-half the strain (12.5% muscle fiber length). Again, there was no difference in maximum tetanic tension after cyclic 12.5% strain with either strain timing. Data from both experiments were analyzed by two-way analysis of variance, which revealed a highly significant effect of strain magnitude (P < 0.001) but no significant effect of stretch timing (P > 0.7). We interpret these data to signify that it is not high force per se that causes muscle damage after eccentric contraction but the magnitude of the active strain (i.e., strain during active lengthening). This conclusion was supported by morphometric analysis showing equivalent area fractions of damaged muscle fibers that were observed throughout the muscle cross section. The active strain hypothesis is described in terms of the interaction between the myofibrillar cytoskeleton, the sarcomere, and the sarcolemma.
Absence of a growth hormone effect on rat soleus atrophy during a 4-day spaceflight
Authors: Jiang B. , Roy R. R. , Navarro C. , Edgerton V. R.
Published: December 2017

The objectives of the present study were to determine the size and enzyme properties of soleus fibers of rats subjected to a 4-day spaceflight (National Aeronautics and Space Administration, STS-41) and the effects of exogenous growth hormone (GH) on the atrophic response of the muscle. Four groups of rats were studied: 1) control (Con), 2) Con plus GH treated (Con + GH), 3) flight (Fl), and 4) F1 plus GH treated (Fl + GH). Cross-sectional area and the activities of succinate dehydrogenase and myofibrillar adenosinetriphosphatase (ATPase) were determined in fibers identified in frozen serial cross sections. Fibers were categorized immunohistochemically as slow, fast, or slow-fast on the basis of their reaction with slow and fast myosin heavy-chain (MHC) monoclonal antibodies. Fibers also were categorized as light or dark on the basis of their staining for ATPase at pH 8.6. After the 4-day flight, mean body weight was significantly decreased compared with control. The absolute and relative (muscle wt/body wt) soleus weights were significantly smaller in the Fl and Fl + GH rats compared with their respective ground-based controls. In both flight groups, the cross-sectional area of the light ATPase fibers was significantly smaller (approximately 30%) than control. Three of 11 flight rats had a higher proportion of fibers expressing both slow and fast MHCs than expected on the basis of the fiber type distribution in the 11 control rats. Mean fiber succinate dehydrogenase and ATPase activities were similar among the four groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Airway-parenchymal interdependence and bronchial responsiveness in two highly inbred rat strains
Authors: Dandurand R. J. , Xu L. J. , Martin J. G. , Eidelman D. H.
Published: December 2017

To investigate if airway-parenchymal interdependence may account for differing bronchial responsiveness between inbred rat strains, Fisher and Lewis 12-wk-old male rats were anesthetized, tracheostomized, and placed in a pressure plethysmograph. Functional residual capacity, total lung capacity [lung volume at transpulmonary pressure (PL) of 30 cmH2O], and specific compliance were determined and were found to be similar. Rats were paralyzed and mechanically ventilated. Concentration-response curves were constructed by calculating lung resistance (RL) and lung elastance (EL) after nebulization of saline and then doubling doses of methacholine (0.0625–512 mg/ml). In Fisher (n = 8) and Lewis (n = 7) rats RL and EL were again determined at a lung volume corresponding to 2 cmH2O PL above FRC. The doubling, maximal, and half-maximal effective concentrations were determined for RL and EL. The doubling of effective concentrations of RL and EL were significantly less for Fisher rats. Other groups of Fisher (n = 5) and Lewis (n = 5) rats were similarly exposed to three concentrations of methacholine (64, 128, and 256 mg/ml), and determinations of RL and EL were made at lung volume corresponding to PL of 0, 2, 4, and 8 cmH2O. In both groups, Lewis rats exhibited a significant effect of volume on maximal RL and EL, whereas Fisher rats did not. The absence of volume effect on bronchoconstriction in the hyperresponsive Fisher strain is consistent with the hypothesis that altered airway-parenchymal interdependence contributes to bronchial hyperresponsiveness.
Food restriction-induced transformations in cardiac functional and biochemical properties in rats
Authors: Haddad F. , Bodell P. W. , McCue S. A. , Herrick R. E. , Baldwin K. M.
Published: December 2017

The primary objective of this study was to ascertain if various degrees of marked chronic food restriction (FR) as well as the combination of FR and exercise training of moderate intensity induce changes in the functional properties of the heart that are consistent with previously reported findings indicative of downregulation of high-adenosinetriphosphatase V1 isomyosin expression. Adult female rodents were randomly assigned to one of four experimental groups: 1) free eating, 2) 50% food restricted, 3) 75% food restricted, or 4) 50% food restricted plus treadmill trained. Results show that FR induced significant depression in the functional properties (heart rate, left ventricular pressure, rate of pressure development, and double product) of the heart in all FR groups and that this depression in functional capacity corresponded to the degree of FR. These functional changes were accompanied by significant downregulation of the alpha- and upregulation of the beta-myosin heavy chain gene expressions, as studied at both the mRNA and protein levels. The exercise training induced further alterations in cardiac function; however, these alterations occurred independently of any shifts in isomyosin composition. These results suggest that although severe FR is a potent stimulus to transform both the biochemical and functional properties of the rodent heart, the underlying mechanism(s) concerning these adaptations remains unresolved.
Effects of motor unit losses on strength in older men and women
Authors: Doherty T. J. , Vandervoort A. A. , Taylor A. W. , Brown W. F.
Published: December 2017

The influence of age-associated motor unit loss on contractile strength was investigated in a representative sample of healthy, active young and older men and women. In 24 younger subjects (22–38 yr) and 20 older subjects (60–81 yr) spike-triggered averaging was employed to extract a sample of surface-recorded single motor unit action potentials (S-MUAPs) from the biceps brachii and brachialis muscles. The amplitude of the maximum compound muscle action potential of the biceps brachii and brachialis muscles was divided by the mean S-MUAP amplitude to estimate the numbers of motor units present. The maximum isometric twitch contraction (MTC) and maximum voluntary contraction (MVC) of the elbow flexors were also recorded in 18 of the younger subjects and in all older subjects. The estimated numbers of motor units were significantly reduced (47%, P < 0.001) in older subjects with a mean value of 189 +/- 77 compared with a mean of 357 +/- 97 in younger subjects. The sizes of the S-MUAPs, however, were significantly larger in older subjects (23%, P < 0.01). Significant but less marked age-associated reductions in the MTC (33%, P < 0.05) and MVC (33%, P < 0.001) were also found and were similar for both men and women. These results suggest that motor unit losses, even in healthy active individuals, are a primary factor in the age-associated reductions in contractile strength.
Use of a new index to study relaxation in a vascular model of anaphylactic shock
Authors: Liu X. , Jiang H. , Stephens N. L.
Published: December 2017

We have reported increased smooth muscle shortening ability in ragweed pollen-sensitized saphenous vein (SSV). This may account for the vascular hyperreactivity of anaphylactic shock. We have now investigated relaxation in SSV. Because isotonic relaxation is load and initial contractile element length dependent, we developed an adjusted half-relaxation time index, which was independent of these variables. Muscle activation state was monitored by measuring maximum unloaded velocity. The relaxation index showed no difference between SSV and control saphenous vein after 2.5, 10, and 15 s of electrical stimulation; however, after 1 s of stimulation it was prolonged significantly in SSV. We concluded that the cross bridges activating early in contraction demonstrated prolonged relaxation. Activation state during muscle relaxation spontaneously increased toward the end of relaxation, coincident with a slowing in isotonic re-elongation rate. This was seen only in muscles relaxing from 15 s of stimulation. Our results indicate that 1) the relaxation properties of early cycling (1 s) cross bridges are altered after sensitization; and 2) toward the end of isotonic relaxation, cross-bridge cycling rate increases spontaneously, a phenomenon not previously reported. We speculate that the rapid re-elongation in late relaxation may reactivate muscle.
Muscle-fiber pennation angles are greater in hypertrophied than in normal muscles
Authors: Kawakami Y. , Abe T. , Fukunaga T.
Published: December 2017

Muscle-fiber pennation angles were measured in vivo with the use of ultrasonography to investigate the relationship between fiber pennation and muscle size for 32 male subjects (from untrained subjects to highly trained bodybuilders). From the image of a B-mode ultrasonogram, fiber pennation angles and thickness of triceps brachii were determined, the former as angles between echoes from the interspaces of fascicles and from the aponeurosis of long and medial heads of triceps and the latter as the distance between the fat-muscle and muscle-bone interfaces. The pennation angles were in the range of 15 and 53 degrees for the long head and 9 to 26 degrees for the medial head, which were similar to or greater than the published and the present data on human cadavers. Significant differences were observed between normal subjects and bodybuilders in muscle thickness and pennation angles (P < 0.01), and there were significant correlations between muscle thickness and pennation angles for both long (r = 0.884) and medial (r = 0.833) heads of triceps, suggesting that muscle hypertrophy involves an increase in fiber pennation angles.
Osmolality affects ion and water fluxes and secretion in the ferret trachea
Authors: Price A. M. , Webber S. E. , Widdicombe J. G.
Published: December 2017

Nonisosmolar solutions were placed in the lumen of the ferret trachea in vitro in an organ bath. Hyposmolar (150 mmol/kg) solutions progressively increased in osmolarity over 1 h. Increases in luminal concentration of impermeant blue dextran occurred only after 5 min, suggesting that the initial changes were due to ion rather than water fluxes. With hyperosmolar solutions the osmolarity decreased over 1 h with no change in blue dextran concentration, indicating that ion but not water fluxes were taking place. Cooling the preparation to 4 degrees C greatly reduced the osmolaity changes with hyperosmolar solutions and halved those with hyposmolar solutions, suggesting that active ion transport was involved. Hyposmolar (75–150 mmol/kg) and hyperosmolar (450–900 mmol/kg) solutions both increased albumin output into the lumen, but the response was prevented by cooling the trachea to 4 degrees C. Hyposmolar and hyperosmolar solutions both increased the output of lysozyme from glandular serous cells into the lumen. The response to hyposmolar solutions was stronger. Cooling the trachea abolished the lysozyme response to hyperosmolar solutions. Thus hypo- and hyperosmolar solutions promote ion transport in directions to restore isosmolarity. Both nonisosmolar solutions promote albumin movement by active transport across the mucosa and lysozyme secretion from submucosal glands, responses inhibited by tracheal cooling and therefore dependent on metabolically active processes.
Cerebral blood flow velocity in humans exposed to 24 h of head-down tilt
Authors: Kawai Y. , Murthy G. , Watenpaugh D. E. , Breit G. A. , Deroshia C. W. , Hargens A. R.
Published: December 2017

This study investigates cerebral blood flow (CBF) velocity in humans before, during, and after 24 h of 6 degree head-down tilt (HDT), which is a currently accepted experimental model to simulate microgravity. CBF velocity was measured by use of the transcranial Doppler technique in the right middle cerebral artery of eight healthy male subjects. Mean CBF velocity increased from the pre-HDT upright seated baseline value of 55.5 +/- 3.7 (SE) cm/s to 61.5 +/- 3.3 cm/s at 0.5 h of HDT (P < 0.05), reached a peak value of 63.2 +/- 4.1 cm/s at 3 h of HDT, and remained significantly above the pre-HDT baseline for > or = 6 h of HDT. During upright seated recovery (1–5 h post-HDT), mean CBF velocity decreased to 87% of the pre-HDT baseline value (P < 0.05). Mean CBF velocity correlated well with calculated intracranial arterial pressure (IAP) (r = 0.54, P < 0.001). As analyzed by linear regression, mean CBF velocity = 29.6 + 0.32IAP. These results suggest that HDT increases CBF velocity by increasing IAP during several hours after the onset of microgravity. Importantly, the decrease in CBF velocity after HDT may be responsible, in part, for the increased risk of syncope observed in subjects after prolonged bed rest and also in astronauts returning to Earth.
Intermittent cold exposure causes a muscle-specific shift in the fiber type composition in rats
Authors: Walters T. J. , Constable S. H.
Published: December 2017

We examined the effect of long-term intermittent cold exposure on the fiber type composition of the predominantly type I soleus and the predominantly type IIb extensor digitorum longus (EDL) muscles of rats. Cold exposure was accomplished by submerging the rats in shoulder-deep water, maintained at 20 +/- 0.5 degrees C, for 1 h/day, 5 days/wk, for < or = 19 wk. The efficacy of the treatment was tested by subjecting both groups to 20 degrees C water for 45 min while rectal temperature (Tre) and O2 consumption (VO2) were measured. The cold-exposed group displayed a 22% smaller reduction in Tre (P < 0.05) at the end of the exposure and 23% greater VO2 (P < 0.05) during the same period. Fiber type composition was determined using routine histochemical methods for myosin-adenosinetriphosphatase. In the soleus muscle of the cold-exposed rats, the number of type IIa fibers increased 156% (P < 0.05) and the number of type I fibers decreased 24% (P < 0.05). Cold exposure had no significant influence on the fiber type composition of the EDL muscle. Cold exposure resulted in an increase in citrate synthase activity of 20 and 22% in the soleus and EDL muscles, respectively (P < 0.05). The present study demonstrates that intermittent cold exposure induces a type I-to-type IIa transformation in the soleus muscle while having no influence on the EDL muscle.
Equine plasma and blood volumes decrease with dehydration but subsequently increase with exercise
Authors: Naylor J. R. , Bayly W. M. , Schott H. C. , Gollnick P. D. , Hodgson D. R.
Published: December 2017

The effects of dehydration and 40 min of exercise at approximately 40% of maximal O2 consumption on plasma volume (PV) and blood volume (BV) were studied in six horses. Horses were exercised while euhydrated (C); 4 h after administration of furosemide (1.0 mg/kg i.v.; FDH), which induced isotonic dehydration; and after 30 h without water (DDH), which caused hypertonic dehydration. Dehydration resulted in decreases of 6.3 and 9.9% for PV and BV, respectively, with FDH and 10.7 and 8.5%, respectively, with DDH. During exercise in C, PV and BV increased by 12.7 and 20.0%, respectively; during exercise with FDH, they increased by 11.7 and 26.1%, respectively; and during exercise with DDH, PV decreased by 1.3% from predehydration values, while BV increased by 18.7%. Hematocrit and total plasma protein concentration rose to higher values throughout exercise in FDH and DDH than in C; plasma [Na+] was higher in DDH than in FDH and C, [Cl-] was higher in DDH and lower in FDH than in C, and [K+] was lower in FDH and DDH than in C through exercise and recovery. From these results, we conclude that increases in PV and BV are normal features of low-intensity exercise in the horse. The increases in BV not only augment O2 carriage but also help maintain circulating volume. These increases can be modified by preexercise dehydration, the nature of which affects the extent of modification.
Effects of acute passive smoking on exercise-induced bronchoconstriction in asthmatic children
Authors: Magnussen H. , Lehnigk B. , Oldigs M. , Jorres R.
Published: December 2017

This study was designed to investigate the acute effects of environmental tobacco smoke (ETS) in children with mild asthma during rest and exercise. We studied 13 children [8 males, 5 females; mean age 10 (range 8–13) yr; mean forced expired volume in 1 s (FEV1) 93% (range 82–108%) of predicted] with exercise-induced bronchoconstriction [46 +/- 4% (SE) fall in FEV1 after exercise during cold air breathing]. Children were exposed to ETS (20 ppm carbon monoxide) or ambient air (AA) for 1 h. During the first 54 min of exposure, children were at rest, and during the last 6 min they exercised on a bicycle ergometer (2 W/kg body wt). Spirometry was performed before and during exposure and after exercise. Respiratory symptoms were recorded before and after exposures. In seven children the experiments with AA and ETS were done in duplicate. FEV1 between 5 and 54 min of exposure at rest decreased by 3.2 +/- 0.8% (SE) during AA and by 7.2 +/- 2.3% during ETS exposure compared with preexposure values; the difference between AA and ETS was statistically significant (P = 0.04). The drop in FEV1 was achieved within 5 min and did not change with ongoing exposure. Analysis of individual data revealed that the mean changes during ETS were mainly effected by three children with a significant fall and one child with a significant improvement in FEV1 (P < 0.05). Maximum postexercise fall of FEV1 was 25 +/- 4% after AA and 24 +/- 3% after ETS, which did not differ significantly. Upper and lower respiratory tract symptoms were not significantly different between exposures.(ABSTRACT TRUNCATED AT 250 WORDS)
Transient changes in muscle high-energy phosphates during moderate exercise
Authors: Marsh G. D. , Paterson D. H. , Potwarka J. J. , Thompson R. T.
Published: December 2017

The purpose of this study was to use 31P-nuclear magnetic resonance spectroscopy to examine changes in wrist flexor muscle metabolism during the transitions from rest to steady-state exercise (on-transient) and back to rest (off-transient). Five healthy young males (mean age 25 +/- 2 yr) performed a series of square-wave exercise tests, each consisting of 5 min of moderate-intensity work followed by a 5-min recovery period. The subjects repeated this protocol six times, and each individual's results were pooled before analysis. ATP and intracellular pH did not change significantly during exercise or recovery. Phosphocreatine (PCr) declined progressively at the onset of exercise, reaching a plateau after approximately 2 min. A reciprocal increase in Pi occurred during the onset of exercise. During the recovery period PCr was resynthesized, whereas Pi returned to resting levels. The data were plotted as a function of time and fit with both first- and second-order exponential growth or decay models; however, the second-order model did not significantly improve the fit of the data. Time constants for the first-order model of the on- and off-transient responses for both PCr and Pi were approximately 30 s. These values are nearly identical to the time constants for oxygen consumption during submaximal exercise that have been reported previously by several authors. The results of this study show that the metabolism of muscle PCr during steady-state exercise and recovery can be accurately described by a monoexponential model and, further, suggest that a first-order proportionality exists between metabolic substrate utilization and oxygen consumption.
Caffeine metabolism and epinephrine responses during exercise in users and nonusers
Authors: Van Soeren M. H. , Sathasivam P. , Spriet L. L. , Graham T. E.
Published: December 2017

This study compared the caffeine (CAF) metabolism and the catecholamine and metabolic responses of users and nonusers of caffeine after acute ingestion of caffeine (5 mg/kg) during 1 h of steady-state exercise (50% maximal oxygen consumption). Nonusers (n = 7) completed two exercise trials after ingesting either CAF (5 mg/kg) or placebo (PL). Users (n = 7) underwent three trials designed to control caffeine use and abstained from voluntary CAF intake for 18 days. After 4 days they had a PL trial and in the following 14 days they were given random 6 days of CAF (2 x 2.5 mg.kg-1 x day-1) or PL ingestion followed in each case on the 7th day by a CAF exercise trial identical to that of the nonusers. In nonusers CAF increased (P < 0.05) plasma epinephrine (EPI) concentration above PL values during exercise. Users did not exhibit any increased EPI with CAF, but the EPI response to exercise in all three trials was twofold greater than that of the nonusers' PL trial (P < 0.05). In all trials both groups had identical norepinephrine responses. The groups had similar plasma and urinary caffeine concentration, but plasma dimethylxanthines varied; the users had greater (P < 0.05) theophylline concentration, and the nonusers had a greater (P < 0.05) rise in paraxanthine (PX) concentration. The users and nonusers' plasma free fatty acids (FFA), glycerol and respiratory exchange ratio were similar after ingestion of CAF. Although PX may increase FFA in resting subjects, in this study PX concentrations in nonusers varied from that of the users, yet FFA data were similar.(ABSTRACT TRUNCATED AT 250 WORDS)
Activated polymorphonuclear leukocytes increase low-level chemiluminescence of isolated perfused rat lungs
Authors: Barnard M. L. , Gurdian S. , Turrens J. F.
Published: December 2017

Low-level chemiluminescence was measured in isolated perfused rat lungs subjected to different types of oxidative stress: perfusion with tert-butyl hydroperoxide (t-BOOH) or stimulation of polymorphonuclear cells (PMN). The time required for t-BOOH-dependent lung chemiluminescence to return to background levels was proportional to the concentration of t-BOOH. From the half times of the decay at different t-BOOH concentrations, we estimated that the lungs metabolize organic peroxides at a rate of 0.045 mM/min. Use of a high dose of t-BOOH (3 mM)or pretreatment of lungs with 1,3-bis(2-chloroethyl)-nitrosourea (100 micrograms/ml) to inhibit glutathione reductase produced chemiluminescence that was much greater and did not decay. Stimulation of 5 x 10(7) PMN with 1 micrograms of phorbol myristate acetate resulted in significant increases in chemiluminescence that occurred in the absence of a significant lung weight gain or measurable lipid peroxidation. Perfusion of isolated lungs with superoxide dismutase (100 U/ml) completely inhibited the chemiluminescence response to PMN activation, whereas treatment with 100 microM U-74389F, a lipid-soluble antioxidant, also significantly decreased PMN-dependent chemiluminescence. Neither catalase (2,000 U/ml) nor 100 microM U-78518F, a water-soluble antioxidant, decreased chemiluminescence after PMN activation. These results indicate that low-level chemiluminescence is a sensitive indicator of oxidative stress in the isolated perfused rat lung and provides a tool for devising and characterizing the effectiveness of antioxidant interventions.
Metabolic response to halothane in piglets susceptible to malignant hyperthermia: an in vivo 31P-NMR study
Authors: Decanniere C. , Van Hecke P. , Vanstapel F. , Ville H. , Geers R.
Published: December 2017

Using in vivo 31P-nuclear magnetic resonance spectroscopy, we studied the skeletal muscle metabolism of 17 anesthetized malignant hyperthermia-susceptible piglets and 25 control piglets during and after a halothane stress test. At rest, the phosphocreatine- (PCr) to-ATP ratio was 12% higher in the anesthetized piglets than in the control piglets, which may reflect a higher proportion of fast glycolytic fibers in the former. About 15 min of halothane administration sufficed to provoke onset of a reaction, which was characterized by a reciprocal drop in PCr and an increase in Pi with commencing intracellular acidosis. Halothane was withdrawn after a 20% drop in PCr. Within the next few minutes, intracellular pH dropped sharply and phosphomonoesters (PME) accumulated excessively. ATP was observed to decrease in 8 of the 17 animals. Halothane inhalation provoked a switch of metabolism toward glycolysis. Accumulation of PME suggests a mismatch between glycogenolysis and glycolysis. Despite severe acidification, glycolysis was not completely halted. Recovery of PCr and Pi started approximately 5 min after halothane withdrawal, with a longer time constant for recovery of the former. PME and intracellular pH aberrations lingered and started to recover later. Lost ATP was never restored within the observed recovery period of approximately 20 min.
Structure of parasternal intercostal muscles in the adult hamster: topographic effects
Authors: Kelsen S. G. , Bao S. , Thomas A. J. , Mardini I. A. , Criner G. J.
Published: December 2017

The parasternal intercostals are primary inspiratory muscles like the costal and crural diaphragm. However, the structure of the rib cage and its impedance to inspiration and expiration varies regionally. We questioned whether topographic differences in rib cage structure and impedance were associated with regional differences in parasternal intercostal muscle structure. Therefore, we examined the size and percentage of histochemically stained fibers in the parasternal intercostal muscles in the first, second, third, fourth, and sixth interspaces in the hamster. We observed a rostrocaudal gradient in the percentage and size of slow oxidative (SO), fast oxidative-glycolytic, and fast glycolytic (FG) fibers in the parasternal intercostal muscles. In particular, the percentage of SO decreased while the percentage of FG increased in a rostrocaudal direction in the first through sixth interspaces. In addition, the size of SO and FG fibers increased from the first to sixth interspace. Furthermore, changes in the size and percent of the three fiber types produced, in a rostrocaudal direction, significant reductions in the relative mass of the parasternal intercostal muscle made up of SO fibers and increases in the mass of fast fibers. We speculate that topographical differences in the size and percentage of fast and slow twitch fibers in the parasternal intercostal are likely to alter force-generating capacity of the parasternal muscles in a rostrocaudal direction and likely reflect regional differences in muscle load and/or activity.
Dependence of maximal flow-volume curves on time course of preceding inspiration
Authors: D'Angelo E. , Prandi E. , Milic-Emili J.
Published: December 2017

Thirteen normal subjects, sitting in a body plethysmograph and breathing through a pneumotachograph, performed forced vital capacity maneuvers after a rapid inspiration without or with an end-inspiratory pause (maneuvers 1 and 2) and after a slow inspiration without or with an end-inspiratory pause (maneuvers 3 and 4), the pause lasting 4–6 s. Inspirations were initiated close to functional residual capacity. At all lung volumes, expiratory flow was larger with maneuver 1 than with any other maneuver and, over the upper volume range, larger with maneuver 3 than with maneuver 4, whereas it was similar for maneuvers 2 and 4. Relative to corresponding values with maneuver 4, peak expiratory flow was approximately 16 and approximately 4% larger with maneuvers 1 and 3, respectively, whereas forced expiratory volume in 1 s increased by approximately 5% only with maneuver 1. The time dependence of maximal flow-volume curves is consistent with the presence of viscoelastic elements within the respiratory system (D'Angelo et al. J. Appl. Physiol. 70: 2602–2610, 1991).
Influence of sleep on response to negative airway pressure of tensor palatini muscle and retropalatal airway
Authors: Wheatley J. R. , Tangel D. J. , Mezzanotte W. S. , White D. P.
Published: December 2017

Increased retropalatal airway resistance may be caused by a sleep-induced loss of palatal muscle activity and a diminished ability of these muscles to respond to the increasing intrapharyngeal negative pressure that develops during sleep. To investigate these possibilities, in six normal subjects, we determined the effect of non-rapid-eye-movement sleep on 1) the tensor palatini (TP) electromyogram (EMG) response to rapid-onset negative-pressure generations (NPG) in the upper airway and 2) the collapsibility of the retropalatal airway during these NPGs. During wakefulness, the change in TP EMG from basal to peak levels (during NPG) was 19.8 +/- 3.2 arbitrary units (P < 0.005). This was markedly reduced during sleep (3.6 +/- 1.5 arbitrary units; P < 0.001). The latency of the TP EMG response was 48.5 +/- 5.6 ms during wakefulness but was prolonged during sleep (105.0 +/- 12.2 ms; P < 0.02). The peak transpalatal pressure during NPG (a measure of airway collapse) was 2.1 +/- 0.7 cmH2O during wakefulness and increased to 5.3 +/- 0.8 cmH2O during sleep (P < 0.05). We conclude that the brisk reflex response of the TP muscle to negative pressure during wakefulness is markedly reduced during non-rapid-eye-movement sleep, in association with a more collapsible retropalatal airway. We speculate that the reduction in this TP reflex response contributes to retropalatal airway narrowing during sleep in normal subjects.
Effects of eccentric exercise on insulin secretion and action in humans
Authors: King D. S. , Feltmeyer T. L. , Baldus P. J. , Sharp R. L. , Nespor J.
Published: December 2017

The effects of an exhaustive bout of eccentric exercise on insulin secretion and action were determined using the hyperglycemic clamp technique. Clamps were performed on eight healthy men after 7 days of inactivity and approximately 36 h after a bout of eccentric exercise. Eccentric exercise consisted of 10 sets of 10 repetitions of combined knee extensions and flexions for each leg at a mean torque 84 +/- 5% of peak concentric torque. During the hyperglycemic clamp procedure, plasma glucose concentration was acutely raised to 10 mmol/l and was maintained near this level for 120 min. Arterialized blood samples were obtained from a heated hand vein to determine plasma glucose and insulin concentrations. Eccentric exercise appeared to produce marked muscle damage, as indicated by a 50-fold increase in plasma creatine phosphokinase (100 +/- 17 vs. 5,209 +/- 3,811 U/l, P < 0.001) and subjective reports of muscle soreness. Peak insulin response during the early phase (0–10 min) of the hyperglycemic clamp was higher after eccentric exercise (183 +/- 38 microU/ml) than after the control clamp (100 +/- 23 microU/ml, P < 0.005). Late-phase (10- to 120-min) insulin response was not altered after eccentric exercise. Peak plasma C-peptide concentrations were higher during the early phase (5.0 +/- 0.7 vs. 4.3 +/- 0.8 ng/ml, P < 0.05) and the late phase (7.5 +/- 0.9 vs. 5.4 +/- 0.6 ng/ml, P < 0.05). Prior eccentric exercise had no significant effect on whole body glucose disposal or glucose disposal rate adjusted for prevailing plasma insulin concentration. These data provide evidence that a single bout of eccentric exercise causes an increase in pancreatic beta-cell insulin secretion in response to hyperglycemia.
Examination of data normalization procedures for expressing peak VO2 data
Authors: Toth M. J. , Goran M. I. , Ades P. A. , Howard D. B. , Poehlman E. T.
Published: December 2017

Peak O2 uptake (VO2) has traditionally been compared among individuals differing in body composition by dividing measured values (1/min) by fat-free mass (FFM) (i.e., ratio method). However, the ability of the ratio method to mathematically remove the confounding influence of FFM from peak VO2 has recently been questioned. Therefore, we compared the effectiveness of the ratio method vs. regression modeling to normalize peak VO2 in a large cohort of males and females for differences in FFM. Regression modeling adjusts peak VO2 according to the relationship derived from the regression of peak VO2 on FFM. Results showed that peak VO2 was 60% higher in males (3.53 +/- 1.01/min) than in females (2.22 +/- 0.6 l/min; P < 0.01). With the ratio method (i.e., peak VO2/FFM), peak VO2 was 15% higher in males (54.6 +/- 12 ml.kg FFM-1.min-1) than in females (47.4 +/- 11 ml.kg FFM-1.min-1; P < 0.01). In contrast, when a regression-based approach was employed to normalize values, no significant difference in adjusted peak VO2 was observed between males and females (3.04 +/- 0.9 vs. 3.01 +/- 1.0 l/min). In conclusion, dividing peak VO2 by FFM can produce spurious results, because this approach does not take into account the nonzero intercept. Therefore, a regression-based approach should be used to normalize peak VO2.
Fractal dimension of heart rate time series: an effective measure of autonomic function
Authors: Yeragani V. K. , Srinivasan K. , Vempati S. , Pohl R. , Balon R.
Published: December 2017

Previous studies suggested that heart rate (HR) time series may be more appropriately analyzed by nonlinear techniques because of the nonlinear nature of these data. In this study, we quantified the complexity of the HR time series, using fractal dimension, a previously described measure developed to study axonal growth, which quantifies the space-filling propensity and convolutedness of a waveform, and compared these results with another recently used measure, approximate entropy. Fractal dimension and approximate entropy of HR time series (unfiltered) correlate highly with each other and also with the high-frequency power (0.2–0.5 Hz) and, hence, appear to reflect vagal modulation of HR variability. These measures were also statistically more consistent and effective than measures of spectral analysis. Fractal dimension of the midfrequency time series of HR (filtered with a pass band of 0.05–0.15 Hz) also appears to be a statistically effective measure of relative sympathetic activity, especially in the standing posture.
Pulmonary diffusing capacity after maximal exercise
Authors: Manier G. , Moinard J. , Stoicheff H.
Published: December 2017

To determine the effect of maximal exercise on alveolocapillary membrane diffusing capacity (Dm), 12 professional handball players aged 23.4 +/- 3.3 (SD) yr were studied before and during early recovery from a progressive maximal exercise [immediately (t0), 15 min, and 30 min (t30) after exercise]. Lung capillary blood volume and Dm were determined in a one-step maneuver by simultaneous measurement of CO and NO lung transfer (DLCO and DLNO, respectively) with use of the single-breath breath-hold method. At t0, DLCO was elevated (13.1 +/- 12.0%; P < 0.01) but both DLNO and Dm for CO remained unchanged. Between t0 and t30, both DLCO and DLNO decreased significantly. At t30, DLCO was not different from the control resting value. DLNO (and consequently Dm for CO) was significantly lower than the control value at t30 (-8.9 +/- 8.1%; P < 0.01). Lung capillary blood volume was elevated at t0 (18.0 +/- 19.0%; P < 0.01) but progressively decreased to near control resting values at t30. Differences in the postexercise kinetics of both DLCO and DLNO point to a role of the transient increase in pulmonary vascular recruitment during the recovery period. We concluded that Dm was somewhat decreased in the 30 min after maximal exercise of short duration, but the exact pulmonary mechanisms involved remain to be elucidated.
Effects of immobilizing the cat peroneus longus muscle on the activity of its own spindles
Authors: Gioux M. , Petit J.
Published: December 2017

The peroneus longus muscle of 10 cats were immobilized by fixating the distal tendon on the fibula at one of two length: neutral (length for a 90 degrees flexion of the ankle joint; 5 cats) or short (length for a full extension of the joint; 5 cats). Spindle afferent discharges were studied after 2 (4 cats) or 5 wk (6 cats) of immobilization and compared with those of four control animals. In each muscle, the discharges of nearly all primary and one of secondary muscle spindle endings were recorded during 2-mm ramp-and-hold stretches applied at different initial muscle lengths. A very slight increase in both the static discharge and the dynamic index of primary endings was observed in passive spindles. The increase in connective tissue that occurs in immobilized muscle and reduces muscle compliance was likely the sole alteration responsible for this constant effect. The responses to stretches of primary endings during stimulation of static and dynamic gamma-axons were not altered. Muscle immobilization at short length, even if spindle properties are not altered, can be expected to reduce the overall amount of group Ia afferent impulses with possible long-term changes on motoneuron properties.
Exercise training alters myogenic responses in porcine coronary resistance arteries
Authors: Muller J. M. , Myers P. R. , Laughlin M. H.
Published: December 2017

The purpose of this study was to test the hypothesis that myogenic responsiveness in porcine coronary resistance arteries is attenuated by exercise training. Twenty-four female Yucatan miniature swine were randomly separated into two groups of 12 pigs: exercise trained (ET) and sedentary control (SED). The ET pigs were trained on a motor-driven treadmill for 16–22 wk while the SED pigs remained confined to their pens. After training, heart weight-to-body weight ratio, skeletal muscle oxidative capacity, and exercise tolerance were significantly increased in ET pigs compared with SED pigs. Coronary resistance arteries 75–150 microns diam were isolated for in vitro evaluation of myogenic responses to changes in intraluminal pressure in the absence of intraluminal flow. Coronary resistance arteries from ET and SED pigs developed spontaneous tone at 40 mmHg intraluminal pressure. Active changes in diameter measured in response to intraluminal pressures < 40 mmHg were similar in coronary resistance arteries from ET and SED pigs. When pressure was raised above 40 mmHg, myogenic constriction was greater in coronary resistance arteries from ET pigs, as indicated by significantly greater reductions in diameter. At 60 and 70 mmHg intraluminal pressure, constriction was 8 and 16% greater, respectively, in resistance arteries from ET pigs. After maximal relaxation with sodium nitroprusside (100 microM), passive diameter changes measured in response to changes in intraluminal pressure from 10 to 80 mmHg were not significantly different in coronary resistance arteries from ET and SED pigs. We conclude that, contrary to our hypothesis, exercise training in pigs enhances myogenic constrictor responses in coronary resistance arteries.(ABSTRACT TRUNCATED AT 250 WORDS)
A method for chronic membrane plasmapheresis in the rat
Authors: Follette D. B. , Kerr D. , Nasca T. J. , Euler H. H. , Pinevich A. J.
Published: December 2017

Therapeutic apheresis as applied to humans may encompass a single treatment or numerous treatments for disorders ranging from acute poisoning to severe chronic autoimmune disease. However, the mechanisms of beneficial effects of apheresis are not well characterized. Utilizing a miniaturized hollow-fiber membrane system, we have developed a reliable technique for long-term vascular access in the rat that permits repetitive plasmapheresis. We established vascular access in 14 animals, with 8 and 6 rats randomized to 3- and 7-wk experimental periods, respectively. Immunoglobulin levels of blood samples obtained immediately before and after each plasmapheresis were measured to examine membrane filtration characteristics. Overall, 100% of the animals survived and 93% successfully completed their assigned experimental periods. Mean decrease of immunoglobulin G and M levels for 28 plasmapheresis treatments in five rats was 66.9 +/- 8.1 and 61.0 +/- 7.3% (SD), respectively, indicating effective membrane filtration. This model of apheresis can be applied to several disorders in the rat, including, but not limited to, spontaneous insulin-dependent diabetes mellitus and experimental inflammatory bowel disease.
Diaphragm injury and myofibrillar structure induced by resistive loading
Authors: Reid W. D. , Huang J. , Bryson S. , Walker D. C. , Belcastro A. N.
Published: December 2017

The purpose of this study was to determine whether ventilatory failure is associated with muscle fiber damage and myofibrillar protein alterations. Ventilatory failure was induced by tightening a polyvinyl band around the trachea of hamsters (TB; n = 14) for 6 days, which resulted in severe respiratory acidosis (PCO2: 97.9 +/- 29.6 vs. 51.6 +/- 19.6 Torr; pH: 7.16 vs. 7.35), hypoxemia (PO2: 42.8 +/- 16.8 vs. 65.9 +/- 25.8 Torr), and increased pulmonary resistance (1.89 +/- 1.61 vs. 0.29 +/- 0.27 cmH2O.ml-1 x min; P < 0.05). The point-counting technique of hematoxylin- and eosin-stained cross sections showed a higher area fraction of abnormal muscle and inflammatory cells in the costal [0.133 +/- (SE) 0.33 vs. 0.040 +/- 0.010] and crural regions (0.069 +/- 0.020 vs. 0.012 +/- 0.003) of the diaphragm in TB hamsters than in control hamsters. Electron micrographs revealed sarcomeric disruption and Z band streaming in the diaphragm of TB hamsters. Myofibrillar changes of the diaphragm associated with ventilatory failure were quantitative (i.e., a lower yield of purified myofibrils) but not qualitative (similar sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profiles); however, sulfhydryl group reactivities were reduced (P < 0.05). Proteolysis of purified myofibrils from the diaphragm digested with calpain showed faster degradation rates for tropomyosin and alpha-actinin but not for all proteins for the TB animals. Ventilatory failure induced by resistive loading was associated with diaphragm injury; some of this injury was linked to changes in myofibrillar complexes, specifically their susceptibility to calpain-mediated degradation.
Acute effects of hindlimb unweighting on satellite cells of growing skeletal muscle
Authors: Schultz E. , Darr K. C. , Macius A.
Published: December 2017

The proliferative behavior of satellite cells in growing rat soleus and extensor digitorum longus muscles was examined at short periods after initiation of hindlimb unweighting. Mitotic activity of satellite cells in both muscles decreased below weight-bearing control levels within 24 h of initiation of hindlimb unweighting. This satellite cell response was > or = 48 h before any atrophic morphological changes that take place in the muscles. Suppression of mitotic activity was most severe in the soleus muscle where continuous infusion of label demonstrated that virtually all mitotic activity was abolished between 3 and 5 days. The results of this study suggest that satellite cell mitotic activity is a sensitive indicator of primary atrophic changes occurring in growing myofibers and may be a predictor of future morphological changes.