bluuebunny/crossref_metadata_2025 huggingface dataset:
Ontogeny of integumental calcium in relation to surface area and skin water content in the perinatal rat
Authors: Hoath S. B. , Pickens W. L. , Tanaka R. , Ross R.
Published: December 2017

Calcium is an important regulator of epidermal differentiation and skin biomechanics in many vertebrate species. In this study, we measured total epidermal calcium in the perinatal Sprague-Dawley rat. Values ranged from 12 to 15 mg per 100 g of tissue. These levels were elevated compared with dermis and other soft (nonbone) organs, including brain, kidney, heart, and liver. Administration of radioactive calcium to the pregnant rat resulted in high rates of 45Ca2+ localization in the fetal epidermis 24 h later. From gestational day 20 to postnatal day 3, the epidermis showed progressive dehydration with water content decreasing from 79 to 73%. Dermal hydration over the same period decreased from 91 to 81%. In the neonatal rat (age 0–3 days), linear regression analysis of surface area vs. body weight on a log-log plot yielded a slope of 1.04. This finding contrasts with an expected slope of 0.67 based on simple surface area-to-volume relationships and differs from the empirical 0.75-power law observed in adult bioenergetics. In summary, these results show the perinatal rat is encapsulated by a continuous differentially hydrated calcium-rich epidermal envelope that increases in surface area over the early postnatal period directly as the first power of body mass.
Hepatic adaptations to iron deficiency and exercise training
Authors: Willis W. T. , Jones P. H. , Chengson R. , Dallman P. R.
Published: December 2017

Brooks et al. [Am. J. Physiol. 253 (Endocrinol. Metab. 16): E461-E466, 1987] demonstrated an elevated gluconeogenic rate in resting iron-deficient rats. Because physical exercise also imposes demand on this hepatic function, we hypothesized that exercise training superimposed on iron deficiency would augment the hepatic capacity for amino acid transamination/deamination and pyruvate carboxylation. Sprague-Dawley rats (n = 32) were obtained at weaning (21 days of age) and randomly assigned to iron-sufficient (dietary iron = 60 mg iron/kg diet) or iron-deficient (3 mg iron/kg) dietary groups. Dietary groups were subdivided into sedentary and trained subgroups. Treadmill training was 4 wk in duration, 6 days/wk, 1 h/day, 0% grade. Treadmill speed was initially 26.8 m/min and was decreased to 14.3 m/min over the 4-wk training period. The mild exercise-training regimen did not affect any measured variable in iron-sufficient rats. In contrast, in iron-deficient animals, training increased endurance capacity threefold and reduced blood lactate and the lactate-to-alanine ratio during submaximal exercise by 34 and 27%, respectively. The mitochondrial oxidative capacity of gastrocnemius muscle was increased 46% by training. However, the oxidative capacity of liver was not affected by either iron deficiency or training. Maximal rates of pyruvate carboxylation and glutamine metabolism by isolated liver mitochondria were also evaluated. Iron deficiency and training interacted to increase pyruvate carboxylation by intact mitochondria. Glutamine metabolism was increased roughly threefold by iron deficiency alone, and training amplified this effect to a ninefold increase over iron-sufficient animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Plasma volume, fluid shifts, and renal responses in humans during 12 h of head-out water immersion
Authors: Johansen L. B. , Foldager N. , Stadeager C. , Kristensen M. S. , Bie P. , Warberg J. , Kamegai M. , Norsk P.
Published: December 2017

Changes in plasma volume (PV) throughout 12 h of thermoneutral (34.5 degrees C) water immersion (WI) were evaluated in eight subjects by an improved Evans blue (EB) technique and by measurements of hematocrit (Hct), hemoglobin (Hb), and plasma protein concentrations (Pprot). Appropriate time control studies (n = 6) showed no measurable change in PV. At 30 min of immersion, EB measurements demonstrated an increase in PV of 16 +/- 2% (457 +/- 70 ml). Calculations, however, based on concomitant changes in Hct, Hb, and Pprot showed an increase in PV of only 6.9 +/- 0.9 to 10.0 +/- 0.8% at 30 min of WI. PV values based on EB measurements subsequently declined throughout WI to (but not below) the preimmersion level. Concomitantly, changes in PV calculated from Pprot values remained increased, whereas estimations of changes in PV based on Hct and Hb values returned to prestudy levels after 4 h of immersion. It is concluded that PV initially increases by 16 +/- 2% during WI and does not decline below preimmersion and control levels during 12 h of immersion despite a loss of 0.9 +/- 0.2 liter of body fluid. Furthermore, changes in Hct, Hb, and Pprot do not provide accurate measures of the changes in PV during WI in humans.
Static lung-lung interactions in unilateral emphysema
Authors: Margulies S. S. , Schriner R. W. , Schroeder M. A. , Hubmayr R. D.
Published: December 2017

Motivated by the introduction of single-lung transplantation into clinical practice, we compared the static mechanical properties of the respiratory system in six supine dogs before (at baseline) with those after the induction of unilateral emphysema. Relaxation volume (Vrel), total lung capacity (TLC), and static compliance of the emphysematous lung increased to 214 +/- 68, 186 +/- 39, and 253 +/- 95% (SD) of baseline, respectively. Vrel of the nonemphysematous lung fell to 81 +/- 28% of baseline, with no significant change in TLC of the nonemphysematous lung or its pressure-volume relationship, indicating that unilateral hyperinflation does not cause dropout of contralateral lung units. After unilateral emphysema, the chest wall shifted to a higher unstressed or neutral volume (when pleural pressure equals atmospheric pressure) in three of six animals, minimizing the anticipated decrease in lung recoil pressure at the higher respiratory system Vrel. The pattern of relative lung emptying in the intact dog and in the excised lungs was similar during stepwise deflations from TLC, suggesting that mean pleural pressure of the hemithoraces is equal. We conclude that in the dog the static volume distribution between emphysematous and nonemphysematous lungs is determined only by differences in lung recoil and compliance.
Effect of phrenic afferent stimulation on pattern of respiratory muscle activation
Authors: Ward M. E. , Deschamps A. , Roussos C. , Hussain S. N.
Published: December 2017

Ventilation and electromyogram (EMG) activities of the right hemidiaphragm, parasternal intercostal, triangularis sterni, transversus abdominis, genioglossus, and alae nasi muscles were measured before and during central stimulation of the left thoracic phrenic nerve in 10 alpha-chloralose anesthetized vagotomized dogs. Pressure in the carotid sinuses was fixed to maintain baroreflex activity constant. The nerve was stimulated for 1 min with a frequency of 40 Hz and stimulus duration of 1 ms at voltages of 5, 10, 20, and 30 times twitch threshold (TT). At five times TT, no change in ventilation or EMG activity occurred. At 10 times TT, neither tidal volume nor breathing frequency increased sufficiently to reach statistical significance, although the change in their product (minute ventilation) was significant (P less than 0.05). At 20 and 30 times TT, increases in both breathing frequency and tidal volume were significant. At these stimulus intensities, the increases in ventilation were accompanied by approximately equal increases in the activity of the diaphragm, parasternal, and alae nasi muscles. The increase in genioglossus activity was much greater than that of the other inspiratory muscles. Phrenic nerve stimulation also elicited inhomogeneous activation of the expiratory muscles. The transversus abdominis activity increased significantly at intensities from 10 to 30 times TT, whereas the activity of the triangularis sterni remained unchanged. The high stimulation intensities required suggest that the activation of afferent fiber groups III and IV is involved in the response. We conclude that thin-fiber phrenic afferent activation exerts a nonuniform effect on the upper airway, rib cage, and abdominal muscles and may play a role in the control of respiratory muscle recruitment.
Effects of acute oligohydramnios on respiratory system of fetal sheep
Authors: Savich R. D. , Guerra F. A. , Lee C. C. , Padbury J. F. , Kitterman J. A.
Published: December 2017

Prolonged oligohydramnios, or a lack of amniotic fluid, is associated with pulmonary hypoplasia and subsequent perinatal morbidity, but it is unclear whether short-term or acute oligohydramnios has any effect on the fetal respiratory system. To investigate the acute effects of removal of amniotic fluid, we studied nine chronically catheterized fetal sheep at 122–127 days gestation. During a control period, we measured the volume of fluid in the fetal potential airways and air spaces (VL), production rate of that fluid, incidence and amplitude of fetal breathing movements, tracheal pressures, and fetal plasma concentrations of cortisol, epinephrine, and norepinephrine. We then drained the amniotic fluid for a short period of time [24–48 h, 30.0 +/- 4.0 (SE) h] and repeated the above measurements. The volume of fluid drained for the initial studies was 1,004 +/- 236 ml. Acute oligohydramnios decreased VL from 35.4 +/- 2.9 ml/kg during control to 22.0 +/- 1.6 after oligohydramnios (P less than 0.004). Acute oligohydramnios did not affect the fetal lung fluid production rate, fetal breathing movements, or any of the other measured variables. Seven repeat studies were performed in six of the fetuses after reaccumulation of the amniotic fluid at 130–138 days, and in four of these studies the lung volume also decreased, although the overall mean for the repeat studies was not significantly different (27.0 +/- 5.2 ml/kg for control vs. 25.5 +/- 5.5 ml/kg for oligohydramnios). Again, none of the other measured variables were altered by oligohydramnios in the repeat studies.(ABSTRACT TRUNCATED AT 250 WORDS)
Failure of pulmonary acidosis to increase respiratory drive
Authors: Orr J. A. , Carrithers J. A. , Liu F. , Shirer H. W.
Published: December 2017

Experiments were performed to determine whether increases in acidity isolated to the pulmonary circulation would stimulate hypothesized pulmonary chemoreceptors and increase respiratory drive in the anesthetized paralyzed mechanically ventilated cat (n = 9). Respiratory drive was assessed by measuring the frequency and amplitude of the integrated phrenic neurogram. To create an isolated pulmonary acidosis, blood returning to the lung was acidified by infusion of 0.3 M lactic acid (1.91 ml/min) into the inferior vena cava, while systemic arterial pH was restored to near normal levels by simultaneous infusion of base (0.3 M NaOH) into the left atrium. Six minutes after the start of this dual infusion of acid and base, right ventricular (pulmonary) pH decreased from 7.286 to 7.179 and PCO2 increased 7 Torr. Systemic arterial pH and PCO2 were unchanged from measurements immediately before the infusion. This level of pulmonary acidosis failed to increase respiratory drive as assessed by phrenic activity. To test the sensitivity of the preparation to known systemic arterial chemical stimuli, a combined pulmonary and systemic acidosis was elicited by infusion of 0.3 M lactic acid into the inferior vena cava and 0.3 M NaCl into the left atrium. This infusion significantly lowered both systemic arterial and pulmonary arterial pH (7.343 to 7.155 for systemic arterial pH and 7.286 to 7.067 for pulmonary pH) and increased phrenic efferent activity 45%. We conclude that phrenic efferent activity is unaffected by moderate reductions in the pH of the pulmonary circulation in the absence of a significant systemic arterial acidosis.(ABSTRACT TRUNCATED AT 250 WORDS)
Proliferation of jejunal mucosal cells in rats flown in space
Authors: Sawyer H. R. , Moeller C. L. , Phillips R. W. , Smirnov K. L.
Published: December 2017

To examine the effects of spaceflight on the proliferation and turnover of jejunal mucosal cells, we compared the percentages of mitotic cells present in the crypts of Lieberkuhn in the proximal, middle, and distal jejunum in each of five rats flown on the COSMOS 2044 mission and in rats included in the vivarium, synchronous, and caudal-elevated groups. On the basis of the data obtained, there was no difference in mitotic indexes between animals in the flight and vivarium (ground control) groups. Thus it appears that the ability of jejunal mucosal cells to proliferate is not affected by microgravity conditions associated with spaceflight. Although the length of villi and depth of crypts were reduced in flight animals compared with those in the vivarium group, the observed reduction is probably attributable to changes in the connective tissue core of villi and is not likely due to an impairment of the proliferation and migration of jejunal mucosal cells.
Effect of spaceflight on lymphocyte proliferation and interleukin-2 production
Authors: Nash P. V. , Konstantinova I. V. , Fuchs B. B. , Rakhmilevich A. L. , Lesnyak A. T. , Mastro A. M.
Published: December 2017

Studies of peripheral blood lymphocytes from astronauts indicate that microgravity depresses T-cell responsiveness. However, this effect has not been examined in cells of peripheral lymphatic tissue, where most lymphocytes are located. In this study, inguinal lymph node lymphocytes from rats flown on the COSMOS 2044 mission were tested for proliferation and interleukin-2 (IL-2) production. Cells cultured with mitogenic lectins, phorbol ester, and calcium ionophore, or T-cell mitogen and lymphokine, were assayed for DNA synthesis by [3H]thymidine incorporation. Lymphocytes incubated with a T-cell mitogen alone also were tested for IL-2 production. Proliferation of lymphocytes from flight rats was not significantly different from controls for any of the mitogens tested. Furthermore, lymph node lymphocytes from flight rats was not significantly different from controls for any of the mitogens tested. Furthermore, lymph node lymphocytes from control and flown rats produced similar amounts of IL-2. Thus microgravity may act on lymphocytes in a tissue-specific manner, a new finding that could impact on the evaluation of spaceflight effects on immunocompetence.
Effects of microgravity on the composition of the intervertebral disk
Authors: Pedrini-Mille A. , Maynard J. A. , Durnova G. N. , Kaplansky A. S. , Pedrini V. A. , Chung C. B. , Fedler-Troester J.
Published: December 2017

The lumbar annuli of rats flown on COSMOS 2044 were compared with those of three control groups and a tail-suspension experimental model. The wet and dry weights of the annuli were significantly smaller (P less than 0.05) in the flight group than in three control groups. The collagen-to-proteoglycan ratio was significantly greater (P less than 0.001) in the flight group than in the three control groups, but there were no detectable changes in the relative proportions of type I and II collagen or in the number of pyridinoline cross-links. When the annuli were immersed in water for 2 h, more proteoglycans (P less than 0.001) leached from the annuli of flown rats than from the tissue of control animals, suggesting abnormal or smaller proteoglycans. Safranin-O indicated a normal spatial distribution of the proteoglycans within the annulus. Tail suspension did not affect the size of the annuli, but more proteoglycans (P less than 0.05) leached from the tissue of suspended animals than from the normal annuli. The reasons for smaller disks and the abnormal ratio between the fibrous collagenous network and the proteoglycan gel in the flight group are unknown at this time. It is, however, probable that these changes may affect the biomechanical functions of the annulus, although they may be temporary and totally reversible if injuries are avoided in the interim period.
Adaptations of young adult rat cortical bone to 14 days of spaceflight
Authors: Vailas A. C. , Vanderby R. , Martinez D. A. , Ashman R. B. , Ulm M. J. , Grindeland R. E. , Durnova G. N. , Kaplansky A.
Published: December 2017

To determine whether mature humeral cortical bone would be modified significantly by an acute exposure to weightlessness, adult rats (110 days old) were subjected to 14 days of microgravity on the COSMOS 2044 biosatellite. There were no significant changes in peak force, stiffness, energy to failure, and displacement at failure in the flight rats compared with ground-based controls. Concentrations and contents of hydroxyproline, calcium, and mature stable hydroxylysylpyridinoline and lysylpyridinoline collagen cross-links remained unchanged after spaceflight. Bone lengths, cortical and endosteal areas, and regional thicknesses showed no significant differences between flight animals and ground controls. Our findings suggest that responsiveness of cortical bone to microgravity is less pronounced in adult rats than in previous spaceflight experiments in which young growing animals were used. We hypothesize that 14 days of spaceflight may not be sufficient to impact the biochemical and biomechanical properties of cortical bone in the mature rat skeleton.
Effects of microgravity and tail suspension on enzymes of individual soleus and tibialis anterior fibers
Authors: Chi M. M. , Choksi R. , Nemeth P. , Krasnov I. , Ilyina-Kakueva E. , Manchester J. K. , Lowry O. H.
Published: December 2017

Selected enzymes of energy metabolism were measured in random individual fibers of soleus and tibialis anterior (TA) muscles from rats exposed for 2 wk to spaceflight (F) aboard COSMOS 2044 or tail suspension (T) and from synchronous controls. Average size of soleus fibers (dry weight per unit length) was reduced 37% in F and T fibers; there was little change in TA fibers. Enzyme changes were more pronounced in soleus than in TA fibers. Three enzymes characteristic of fast-twitch muscles, pyruvate kinase, glycerol-3-phosphate dehydrogenase, and 1-phosphofructokinase, were elevated in F and T soleus fibers, but changes in phosphofructokinase were not statistically significant. 3-Ketoacid-CoA transferase, characteristic of slow-twitch muscles, did not change significantly in either F or T fibers. Hexokinase, usually moderately higher in slow- than in fast-twitch muscles, increased markedly in both F and T fibers. In TA fibers analyzed for hexokinase, malate dehydrogenase, phosphohexoisomerase, and pyruvate kinase, only hexokinase and malate dehydrogenase showed significant changes. Hexokinase increased 83% in one of two T muscles. Enzyme data for TA fibers typed by myosin adenosinetriphosphatase were more informative: phosphofructokinase, phosphorylase, and glycerol-3-phosphate dehydrogenase were increased in type IIb fibers of either F or T muscles or both. Malate dehydrogenase was not changed in fibers of any type in either F or T muscle.
Intrinsic properties of pharyngeal and diaphragmatic respiratory motoneurons and muscles
Authors: van Lunteren E. , Dick T. E.
Published: December 2017

Breathing is a complex act requiring the coordinated activity of multiple groups of muscles. Thoracic and abdominal respiratory muscles expand and contract the lungs, whereas pharyngeal and laryngeal respiratory muscles maintain upper airway patency and regulate upper airway resistance. An appreciation of the importance of the latter muscle group in maintaining ventilatory homeostasis and in the pathophysiology of sleep apnea has led to extensive studies examining the neural regulation of pharyngeal dilator muscles. The present review examines the role of heterogeneity in motoneuron and muscle properties in determining the diversity in the electrical and mechanical behaviors of thoracic compared with pharyngeal muscle groups. Specifically, phrenic and hypoglossal motoneuron electrophysiological properties influence whether and the extent to which these neurons will fire in response to a given synaptic input arising from chemo- and mechanoreceptors and from respiratory and nonrespiratory pattern generators. Furthermore, thoracic and pharyngeal muscle properties determine the mechanical response to motoneuronal activity, including the speed of contraction, relationships between motoneuron firing frequency and force production, and whether force is maintained during repetitive activation. Heterogeneity in the functional capabilities of these motoneurons and muscles is in turn determined by diversity of their structural and biochemical properties. Thus, intrinsic properties of respiratory motoneurons and muscles act in concert with neuronal drives in defining the complex electrical and mechanical behavior of pharyngeal and thoracic respiratory motor systems.
Phospholipases introduced into the hypophase affect the surfactant film outlining a bubble
Authors: Enhorning G. , Shumel B. , Keicher L. , Sokolowski J. , Holm B. A.
Published: December 2017

The hypophase exchanger is a recently developed device that makes it possible to replace the liquid in the sample chamber of a pulsating bubble surfactometer, after a bubble has been formed, without changing the size of the bubble. A surfactant film outlining the bubble will retain its surface properties, provided the liquid entering the sample chamber and replacing the hypophase is inert. If, on the other hand, the new hypophase consists of a phospholipase solution, the physical properties of the film are seriously affected. It was found that when phospholipase C, even at low concentration, entered the sample chamber, the physical properties were significantly changed. Phospholipase A2 had to be added at a higher concentration to exert a similar effect. It is postulated that the site of action of phospholipase A2 may be partly protected in the hydrophobic region of the tightly packed surfactant film.
Reduction of oxylabile CO2 in human blood by lactate
Authors: Boning D. , Schunemann H. J. , Maassen N. , Busse M. W.
Published: December 2017

The influence of lactic acid, hydrochloric acid, and sodium lactate addition (10 mmol/l each) on oxylabile CO2 was investigated in blood of male subjects after equilibration at 37 degrees C with 3, 6, and 10% CO2 in N2 and O2, respectively. The total CO2, pH in whole blood and erythrocytes, oxygen saturation, hemoglobin concentration, and hematocrit value were measured. With these data we calculated bicarbonate and carbamate concentrations and the corresponding differences between oxygenated and deoxygenated blood. The amount of oxylabile bicarbonate was not systematically influenced by the various experimental conditions. The carbamate content, however, was larger in deoxygenated than in oxygenated blood (up to 0.08 mol/mol hemoglobin) only in the absence of lactate. In the presence of lactic acid as well as sodium lactate, the carbamate content in oxygenated blood was higher by 0.06–0.13 mol/mol hemoglobin than in deoxygenated blood. The lactate effect even increased after 2,3-diphosphoglycerate depletion. We suggest, therefore, a competition between CO2 and the lactate ion at the NH2-terminal valine of the beta-globin chain in deoxygenated hemoglobin.
Cardiovascular responses in black and white males during exercise
Authors: Berry M. J. , Zehnder T. J. , Berry C. B. , Davis S. E. , Anderson S. K.
Published: December 2017

Previous investigations have shown blacks to have a significantly lower resting heart rate (HR) compared with whites. Our purpose was to determine if this difference exists during submaximal exercise and to compare other cardiovascular responses during submaximal exercise in black and white males. Sixteen black and 16 white males matched on age, body surface area, and maximal O2 consumption exercised at 0, 50, and 100 W on a cycle ergometer. HR, O2 consumption, and cardiac output via CO2 rebreathing were measured at rest and at each work rate. Stroke volume was then calculated. O2 consumption was not significantly different between blacks and whites at rest or at work rates of 0, 50, or 100 W. Cardiac output increased from rest with 0, 50, and 100 W work for both blacks and whites (6.1 to 13.0, 14.4, and 16.9 l/min and 5.7 to 12.2, 14.3, and 16.3 l/min, respectively). The differences in cardiac output between blacks and whites at rest and all work rates were not statistically significant. At rest and work rates of 0, 50, and 100 W, HR was significantly lower in blacks compared with whites (71, 99, 108, and 119 beats/min vs. 80, 107, 114, and 127 beats/min, respectively). The lower HR in blacks compared with whites was accompanied by a trend toward a higher stroke volume at rest and work rates of 0, 50, and 100 W (85.2, 130.3, 134.7, and 142.9 ml vs. 72.5, 114.9, 126.4, and 127.4 ml, respectively). No differences in resting blood pressures were found.(ABSTRACT TRUNCATED AT 250 WORDS)
Lymphatic drainage of hypertonic solution from peritoneal cavity of anesthetized and conscious sheep
Authors: Tran L. , Rodela H. , Abernethy N. J. , Yuan Z. Y. , Hay J. B. , Oreopoulos D. , Johnston M. G.
Published: December 2017

Lymphatic drainage of the peritoneal cavity may reduce ultrafiltration in continuous ambulatory peritoneal dialysis. We assessed lymphatic drainage of the peritoneal cavity in sheep under dialysis conditions by cannulation of the relevant lymphatic vessels and compared lymphatic drainage in anesthetized and conscious animals. Lymph was collected from the caudal mediastinal lymph node and the thoracic duct, both of which are involved in the lymphatic drainage of the ovine peritoneal cavity. Volumes of a hypertonic dialysis solution (50 ml/kg 4.25% Dianeal) containing 25 microCi 125I-human serum albumin were instilled into the peritoneal cavity, and lymph flows and the appearance of labeled protein in the lymphatic and vascular compartments were monitored for 6 h. Intraperitoneal pressures increased 4–5 cmH2O above resting levels after infusion of dialysate. On the basis of the appearance of tracer in the lymph, drainage of peritoneal fluid into the caudal lymphatic was calculated to be 3.09 +/- 0.69 and 14.14 +/- 2.86 ml/h in anesthetized and conscious sheep, respectively. Drainage of peritoneal fluid into the thoracic duct preparations was calculated to be 1.32 +/- 0.33 and 14.69 +/- 5.73 ml/h in anesthetized and conscious sheep, respectively. Significant radioactivity was found in the bloodstream, and at least a portion of this was likely contributed by the right lymph duct, which was not cannulated in our experiments.(ABSTRACT TRUNCATED AT 250 WORDS)
Intramuscular pressure and electromyography as indexes of force during isokinetic exercise
Authors: Aratow M. , Ballard R. E. , Crenshaw A. G. , Styf J. , Watenpaugh D. E. , Kahan N. J. , Hargens A. R.
Published: December 2017

A direct method for measuring force production of specific muscles during dynamic exercise is presently unavailable. Previous studies indicate that both intramuscular pressure (IMP) and electromyography (EMG) correlate linearly with muscle contraction force during isometric exercise. The objective of this study was to compare IMP and EMG as linear assessors of muscle contraction force during dynamic exercise. IMP and surface EMG activity were recorded during concentric and eccentric isokinetic plantarflexion and dorsiflexion of the ankle joint from the tibialis anterior (TA) and soleus (SOL) muscles of nine male volunteers (28–54 yr). Ankle torque was measured using a dynamometer, and IMP was measured via catheterization. IMP exhibited better linear correlation than EMG with ankle joint torque during concentric contractions of the SOL (IMP R2 = 0.97, EMG R2 = 0.81) and the TA (IMP R2 = 0.97, EMG R2 = 0.90), as well as during eccentric contractions (SOL: IMP R2 = 0.91, EMG R2 = 0.51; TA: IMP R2 = 0.94, EMG R2 = 0.73). IMP provides a better index of muscle contraction force than EMG during concentric and eccentric exercise through the entire range of torque. IMP reflects intrinsic mechanical properties of individual muscles, such as length-tension relationships, which EMG is unable to assess.
Validation of doubly labeled water for measurement of caloric expenditure in collegiate swimmers
Authors: Jones P. J. , Leitch C. A.
Published: December 2017

To validate doubly labeled water (DLW) in aquatic athletes, energy expenditures (EE) were determined by energy intake/balance (IB) and DLW in free-living collegiate swimmers [n = 8, age 20.1 +/- 1.7 (SD) yr, height 186 +/- 11 cm, weight 74.1 +/- 9.3 kg] over 9 days. EEIB was determined from caloric analysis of duplicate foods to those consumed by subjects and corrected for changes in body composition across the study. For EEDLW, subjects were given 2H2O and H2(18)O on day 0 and 2H2O on day 10. Day 0 and 10 body compositions were measured by use of 2H dilution space, and elimination rates over days 1–10 were determined for 2H and 18O. EEDLW was calculated from CO2 respiratory quotient by use of a food quotient. Fat mass increased (P < 0.01) over the study period. Mean uncorrected energy intake was 3,895 +/- 621 kcal/day. When all eight subjects were compared, EEIB and EEDLW were 3,492 +/- 876 and 3,466 +/- 992 kcal/day, respectively. Data from one subject compared poorly despite repeat isotopic analyses. In the remaining seven subjects, EEIB and EEDLW were 3,444 +/- 925 and 3,556 +/- 1,025 kcal/day, respectively. These data indicate that DLW is a good indicator of EE in groups of swimmers and that energy requirements of swimmers are similar to other athletic groups.
Neuropeptide Y inhibits neurogenic inflammation in guinea pig airways
Authors: Takahashi T. , Ichinose M. , Yamauchi H. , Miura M. , Nakajima N. , Ishikawa J. , Inoue H. , Takishima T. , Shirato K.
Published: December 2017

We examined the effect of neuropeptide Y (NPY) on neurogenic airway microvascular leakage. Male Dunkin-Hartley guinea pigs (250–350 g) were anesthetized with urethan (2 g/kg ip). The cervical artery and vein were cannulated for monitoring blood pressure and injecting drugs, respectively. Atropine and propranolol (each 1 mg/kg i.v.) were administered 30 min before the experiment. After pretreatment with saline (vehicle for NPY) or NPY (1–100 micrograms/kg i.v.), Evans blue dye (30 mg/kg iv) was administered. Then, bilateral vagal nerves were electrically stimulated (5 V, 7 Hz, 5-ms duration for 3 min) to induce airway plasma leakage. Airways were divided into four sections [trachea (Tr), main bronchi, central intrapulmonary airways (IPA), and peripheral IPA] and incubated in formamide (37 degrees C for 16 h). The concentration of Evans blue dye was measured by spectrophotometer. Furthermore, we examined the effect of NPY on exogenous substance P- (0.3 microgram/kg i.v.) induced plasma extravasation. Bilateral vagal stimulation significantly increased leakage of dye in Tr to peripheral IPA. NPY did not affect basal leakage but did significantly inhibit neurogenic plasma extravasation in a dose-dependent manner with maximal inhibitions of 42.3 (Tr), 67.7 (main bronchi), 38.2 (central IPA), and 26.3% (peripheral IPA) at 30 micrograms/kg. Exogenous substance P-induced plasma extravasation was not inhibited by NPY. We conclude that NPY inhibits neurogenic inflammation by prejunctional inhibition of neuropeptide release from airway sensory nerve terminals.
Role of xanthine oxidase in reperfusion injury of ischemic skeletal muscles in the pig and human
Authors: Dorion D. , Zhong A. , Chiu C. , Forrest C. R. , Boyd B. , Pang C. Y.
Published: December 2017

We investigated whether xanthine oxidase (XO) is a major source of oxygen-derived free radicals (oxy-radicals) in the pig and human skeletal muscles. It was observed that xanthine dehydrogenase and XO activities in nonischemic pig latissimus dorsi (LD) and gracilis muscles and human LD and rectus abdominis (RA) muscles were < 0.5 mU/g wet wt. The pig LD muscle hypoxanthine content increased significantly from 0.33 +/- 0.02 to 2.33 +/- 0.44 mumol/g dry wt after 5 h of warm ischemia, but the muscle uric acid content remained unchanged up to 2 h of reperfusion. Similarly, the hypoxanthine content in the human LD and RA muscles increased from 0.33 +/- 0.03 to 0.84 +/- 0.23 mumol/g dry wt after 2.0–3.5 h of warm ischemia, and the muscle uric acid content remained unchanged at the end of 15–90 min of reperfusion. Furthermore, 5 days of allopurinol treatment (25 mg/kg iv twice daily) starting 2 days before ischemia or 3 days of oxypurinol treatment (25 mg/kg iv twice daily) starting 15 min before reperfusion did not attenuate the extent of skeletal muscle necrosis in pig LD muscles subjected to 5 h of ischemia and 48 h of reperfusion. However, deferoxamine treatment (250 mg/kg iv twice daily) starting before or after ischemia, as described above, significantly reduced the extent of pig LD muscle necrosis. Finally, at 2 and 48 h of reperfusion significantly higher muscle neutrophil contents were seen in ischemic than in nonischemic control pig LD muscles. Neutrophil depletion with mechlorethamine (0.75 mg/kg iv) significantly reduced the extent of necrosis in pig LD muscles. These observations indicate that XO is not a major source of oxy-radicals in ischemia/reperfusion injury in the pig gracilis and LD muscles and human RA and LD muscles.
Volume-homeostatic mechanisms in humans during a 12-h posture change
Authors: Norsk P. , Stadeager C. , Johansen L. B. , Warberg J. , Bie P. , Foldager N. , Christensen N. J.
Published: December 2017

On one day six male subjects underwent an upright seated (SEAT) study, and on another day they were subjected to a head-down tilt of 3 degrees (HDT). Compared with SEAT, HDT induced prompt increases in central venous pressure (CVP) from -0.5 +/- 0.8 to 8.3 +/- 0.3 mmHg (P < 0.001) and in arterial pulse pressure of 8–18 mmHg (P < 0.001). CVP stabilized after 6 h at levels 2.4–2.8 mmHg below the peak value. Simultaneously, renal sodium excretion gradually increased over the initial 5 h of HDT and stabilized at a level approximately 125 mumol/min over that of SEAT (P < 0.001). Urine flow rate and solute free water clearance increased during the initial 2–6 h of HDT (P < 0.001) but returned to the level of SEAT thereafter. We concluded that CVP is slightly reduced over 12 h of HDT and that a clear temporal dissociation exists between renal sodium and water handling. We suggest that the combined effect of the sustained suppressions of plasma renin activity and plasma aldosterone and norepinephrine concentrations constitutes a mechanism of the increase in renal sodium excretion.
Intracellular calcium concentration during low-frequency fatigue in isolated single fibers of mouse skeletal muscle
Authors: Westerblad H. , Duty S. , Allen D. G.
Published: December 2017

Low-frequency fatigue is a form of muscle fatigue that follows intense muscle activity and is characterized by reduced tetanic tension at low frequencies of stimulation while tetanic tension at high stimulus frequencies is close to normal. The present experiments were performed on isolated single fibers of mouse in which tension and intracellular calcium concentration ([Ca2+]i) were measured. Fatigue was produced by intermittent short tetani continued until tension had declined to 30% of control. Comparison of low- (30- and 50-Hz) and high- (100-Hz) frequency tetani under control conditions and after 30 min of recovery from fatigue showed that low-frequency fatigue was present. During low-frequency fatigue, tetanic [Ca2+]i was substantially reduced at all stimulus frequencies but there was no change in Ca2+ sensitivity or maximum Ca(2+)-activated tension. One possible cause of the reduced tetanic [Ca2+]i is failure of conduction of the action potential in the T tubule, leading to reduced [Ca2+]i in the center of the fiber. However, imaging of [Ca2+]i across the fiber during low-frequency fatigue did not show any such gradient, suggesting that Ca2+ release is uniform across the fiber. Another possible mechanism is that changes in the Ca2+ pumping ability of the sarcoplasmic reticulum might affect tetanic [Ca2+]i. Measurements of the sarcoplasmic reticulum pump function showed a small slowing of Ca2+ uptake rate during low-frequency fatigue, which is unlikely to cause the reduced tetanic [Ca2+]i. In conclusion, the immediate cause of low-frequency fatigue appears to be a reduced tetanic [Ca2+]i, which is probably a consequence of a reduced Ca2+ release from the sarcoplasmic reticulum.
Angiotensin-converting enzyme inhibition increases collateral-dependent muscle blood flow
Authors: Yang H. T. , Terjung R. L.
Published: December 2017

The purpose of this study was to evaluate the effect of angiotensin-converting enzyme (ACE) inhibition on collateral-dependent blood flow (BF) during exercise. Adult male Sprague-Dawley rats (approximately 320 g) were fed zabicipril, an ACE inhibitor, mixed with powdered food at 0.0, 0.3, and 3.0 mg.kg-1 x day-1 (n = 12/group) for 5–7 days. Under ketamine-acepromazine anesthesia, the carotid and caudal arteries were catheterized for BF determination, and both femoral arteries were ligated to remove the primary route for BF to the distal limb tissue. Later on the same day, collateral-dependent hindlimb BF was determined at two treadmill speeds (15 and 25 m/min at 15% grade) with 85Sr- and 141Ce-labeled 15-microns microspheres. Zabicipril ingestion induced 50 and 65% inhibition of plasma ACE activity in the low- and high-dose group, respectively (P < 0.001). ACE inhibition did not affect body weight, blood pressure, or heart rate of the rats during exercise. However, BFs to the total hindlimb were 44 and 36% higher (P < 0.001) in zabicipril-treated animals than in the zero-dose controls (approximately 45 ml.min-1 x 100 g-1). Furthermore, BFs to the proximal hindlimb, distal hindlimb, and gastrocnemius-plantaris-soleus group were 33–44% greater in drug-treated than in control animals (P < 0.025). Higher speed (25 m/min) failed to further increase muscle BF; therefore peak BFs were likely achieved. These results indicate that collateral-dependent BF was improved by ACE inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
Widespread sites of brain stem ventilatory chemoreceptors
Authors: Coates E. L. , Li A. , Nattie E. E.
Published: December 2017

We produced local tissue acidosis in various brain stem regions with 1-nl injections of acetazolamide (AZ) to locate the sites of central chemoreception. To determine whether the local acidosis resulted in a stimulation of breathing, we performed the experiment in chloralose-urethan anesthetized vagotomized carotid-denervated (cats) paralyzed servo-ventilated cats and rats and measured phrenic nerve activity (PNA) as the response index. Measurements of extracellular brain tissue pH by glass microelectrodes showed that AZ injections induced a change in pH at the injection center equivalent to that produced by an increase in end-tidal PCO2 of approximately 36 Torr and that the change in brain pH was limited to a tissue volume with a radius of < 350 microns. We found AZ injections sites that caused a significant increase in PNA to be located 1) within 800 microns of the ventrolateral medullary surface at locations within traditional rostral and caudal chemosensitive areas and the intermediate area, 2) within the vicinity of the nucleus tractus solitarii, and 3) within the vicinity of the locus coeruleus. Single AZ injections produced increases in PNA that were < or = 69% of the maximum value observed with an increase in end-tidal PCO2. We conclude that central chemoreceptors are distributed at many locations within the brain stem, all within 1.5 mm of the surface, and that stimulation of a small fraction of all central chemoreceptors can result in a large ventilatory response.
Tracheal epithelial permeability to nonelectrolytes: species differences
Authors: Wangensteen O. D. , Schneider L. A. , Fahrenkrug S. C. , Brottman G. M. , Maynard R. C.
Published: December 2017

We developed a new excised tracheal preparation to measure the epithelial permeability of large lipid-insoluble nonelectrolytes and macromolecules. Tracheae were suspended vertically in a Ringer solution bath, and a solution containing labeled test solutes was positioned in the center of the tracheal segment, away from damaged ends. Permeability coefficients, calculated from solute fluxes into the bath, were constant for > or = 2 h at 37 degrees C, and no histological changes were observed. Measurements after epithelial removal with detergent indicate that in the intact trachea the epithelium represents > 90% of the resistance to transport. For the rat trachea, permeability coefficients for sucrose, inulin, and Dextran 20 were 9.22, 2.20, and 0.214 x 10(-7) cm/s, respectively. Values for cat tracheae were similar, those for rabbit tracheae were lower, and those for guinea pig tracheae were markedly greater. With the assumption of transport by diffusion through thin rectangular slits between epithelial cells, the rat and guinea pig data fit a slit width of 7–8 nm, whereas the rabbit and cat data cannot be explained by a model with slits of a single size.
Additive effects of age and silent myocardial ischemia on the left ventricular response to upright cycle exercise
Authors: Fleg J. L. , Schulman S. P. , Gerstenblith G. , Becker L. C. , O'Connor F. C. , Lakatta E. G.
Published: December 2017

To separate the independent effects of age and silent myocardial ischemia on the left ventricular response to aerobic exercise, maximal upright cycle ergometry was performed in three groups: 8 clinically healthy older men [76 +/- 3 (SE) yr] with ischemic electrocardiogram (ECG) and Tl scan responses to prior maximal treadmill exercise (old silent ischemic subjects), 16 age-matched men with normal ECG and Tl scan responses (old controls), and 21 healthy young (33 +/- 1 yr) men (young controls). Although the left ventricular ejection fraction, end-diastolic volume index, and end-systolic volume index were similar in the three groups at rest, with increasing work loads there was a progressive increase in the end-diastolic volume index and a blunted decline in end-systolic volume index in the two older groups, which was most apparent in the old silent ischemic subjects. Thus, at peak effort, end-diastolic volume index was largest in old silent ischemic subjects (101 +/- 6 ml/m2), intermediate in old controls (85 +/- 6 ml/m2), and smallest in young controls (67 +/- 3 ml/m2) (P < 0.002); conversely, left ventricular ejection fraction was highest in young controls (85 +/- 2), intermediate in old controls (76 +/- 3), and lowest in the old silent ischemic group (66 +/- 2) (P < 0.001). At exhaustion the peak systolic pressure-end-systolic volume index was significantly lower in the silent ischemic group than in young controls (6 +/- 1 vs. 25 +/- 4 mmHg.ml-1 x m-2, respectively; P < 0.001) with the old controls in between (16 +/- 5 mmHg.ml-1 x m-2).(ABSTRACT TRUNCATED AT 250 WORDS)
Changes in hormonal concentrations after different heavy-resistance exercise protocols in women
Authors: Kraemer W. J. , Fleck S. J. , Dziados J. E. , Harman E. A. , Marchitelli L. J. , Gordon S. E. , Mello R. , Frykman P. N. , Koziris L. P. , Triplett N. T.
Published: December 2017

Nine eumenorrheic women (age 24.11 +/- 4.28 yr) performed each of six randomly assigned heavy-resistance protocols (HREPs) on separate days during the early follicular phase of the menstrual cycle. The HREPs consisted of two series [series 1 (strength, S) and series 2 (hypertrophy, H)] of three protocols, each using identically ordered exercises controlled for load [5 vs. 10 repetitions maximum (RM)], rest period length (1 vs. 3 min), and total work (J) within each three-protocol series. Blood measures were determined pre-, mid- (after 4 of 8 exercises), and postexercise (0, 5, 15, 30, 60, 90, 120 min and 24 and 48 h). In series 1, a significant (P < 0.05) reduction in growth hormone (GH) was observed at 90 min postexercise for all three protocols. In series 2, the 10-RM protocol with 1-min rest periods (H10/1) produced significant increases above rest in GH concentrations at 0, 5, and 15 min postexercise, and the H10/1 and H5/1 protocols demonstrated significant reductions at 90 and 120 min postexercise. Cortisol demonstrated significant increases in response to the S10/3 protocol at 0 min, to the H10/1 protocol at midexercise and at 0 and 5 min postexercise, and to the H5/1 protocol at 5 and 15 min postexercise. No significant changes were observed in total insulin-like growth factor I, total testosterone, urea, or creatinine for any of the HREPs. Significant elevations in whole blood lactate and ammonia along with significant reductions in blood glucose were observed. Hormonal and metabolic blood variables measured in the early follicular phase of the menstrual cycle varied in response to different HREPs. The most dramatic increases above resting concentrations were observed with the H10/1 protocol, indicating that the more glycolytic HREPs may stimulate greater GH and cortisol increases.
Relationships between in vivo and in vitro measurements of metabolism in young and old human calf muscles
Authors: McCully K. K. , Fielding R. A. , Evans W. J. , Leigh J. S. , Posner J. D.
Published: December 2017

This study compared in vivo measurements of muscle metabolism in humans with magnetic resonance spectroscopy (MRS) and in vitro analysis of biopsies. Healthy subjects [4 young males, 28.2 +/- 6.8 (SD) yr, and 6 older subjects (5 males, 1 female), 66 +/- 6.0 yr] performed a maximal cycle ergometer test, and MRS measurements of the calf muscles and needle biopsies of the lateral gastrocnemius were performed. Biopsies were analyzed for fiber type and citrate synthase (CS) activity. MRS measurements of inorganic phosphate (Pi), phosphocreatine (PCr), ATP, and pH were made using a 1.8-T 78-cm clear-bore magnet-and-spectrometer system. Two or three 5-min bouts of plantar flexion were performed against variable resistance to deplete PCr levels to 50% of resting values (mean end pH 6.99). PCr values during recovery were fit to an exponential curve, and the rate constant (PCrrate) was calculated. PCrrate was used as an index of oxidative metabolism. Older subjects had lower peak O2 uptake (VO2 peak) values (19.2 +/- 5.6 vs. 49.5 +/- 8.1 ml O2.min-1 x kg-1), CS activities (16 +/- 2.8 vs. 25 +/- 2.6 mmol.kg wet wt-1 x min-1), and PCrrate values (25.3 +/- 8. vs. 37.5 +/- 5.3 mmol PCr.kg wet wt-1.min-1) than young subjects. PCrrate correlated with CS activity, and both PCrrate and CS activity correlated with VO2 peak (P < 0.05). No correlations were found between percent fiber type and PCrrate, CS activity, and VO2 peak. These results support studies that showed decreases in muscle metabolism with age in healthy humans and show a good correlation between in vivo and in vitro measurements of oxidative metabolism.
Functional electrical stimulation and respiration during sleep
Authors: Decker M. J. , Haaga J. , Arnold J. L. , Atzberger D. , Strohl K. P.
Published: December 2017

During obstructive sleep apnea (OSA), respiratory activation of upper airway muscles, particularly genioglossus, is ineffective during sleep. Functional electrical stimulation (FES) of muscles reportedly reduces the number and length of OSAs. Our goals were to examine the effect of FES on sensation during wakefulness and on OSA events. Studies were performed in 11 subjects: 4 healthy asymptomatic subjects and 7 patients with OSA. Surface electrodes placed on the submental region produced discomfort; however, during sleep, the stimulus intensity producing arousal was significantly greater than that producing barely tolerable discomfort during wakefulness. Additionally, we developed a protocol for placement of fine-wire electrodes into the neurovascular bundle of the hypoglossal nerve, using recognizable radiographic features and computerized axial tomography as guides. In these patients, while awake, optimal wire placement was associated with visible tongue protrusion without discomfort. With both surface stimulation and fine-wire FES, during sleep the stimulus intensity required to produce obvious electroencephalographic arousal was significantly greater than that producing a barely tolerable sensation while awake. During apneic events, the application of surface stimulation had an inconsistent effect, terminating 22% of the apneas, and fine-wire FES also had a limited impact, terminating 23% of the apneic events. We conclude from our studies that subjects tolerate surface and fine-wire FES to higher stimulus parameters during sleep than during wakefulness but that both approaches have an inconsistent effect on apneas during sleep.