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Resting Value (resting + value)
Selected AbstractsCerebral Metabolism is Influenced by Muscle Ischaemia During Exercise in HumansEXPERIMENTAL PHYSIOLOGY, Issue 2 2003Mads K. Dalsgaard Maximal exercise reduces the cerebral metabolic ratio (O2/(glucose + 1/2lactate)) to < 4 from a resting value close to 6, and only part of this decrease is explained by the ,intent' to exercise. This study evaluated whether sensory stimulation of brain by muscle ischaemia would reduce the cerebral metabolic ratio. In 10 healthy human subjects the cerebral arterial-venous differences (a-v differences) for O2, glucose and lactate were assessed before, during and after three bouts of 10 min cycling with equal workload: (1) control exercise at light intensity, (2) exercise that elicited a high rating of perceived exertion due to a 100 mmHg thigh cuff, and (3) exercise followed by 5 min of post-exercise muscle ischaemia that increased blood pressure by , 20%. Control exercise did not significantly affect the a-v differences. However, during the recovery from exercise with thigh cuffs the cerebral metabolic ratio decreased from a resting value of 5.4 ± 0.2 to 4.0 ± 0.4 (mean ±s.e.m.. P < 0.05) as a discrete lactate efflux from the brain at rest shifted to a slight uptake. Also, following post-exercise muscle ischaemia, the cerebral metabolic ratio decreased to 4.5 ± 0.3 (P < 0.05). The results support the hypothesis that during exercise, cerebral metabolism is influenced both by the mental effort to exercise and by sensory input from skeletal muscles. [source] Changes in Cerebral Blood Flow During and After 48 H of Both Isocapnic and Poikilocapnic Hypoxia in HumansEXPERIMENTAL PHYSIOLOGY, Issue 5 2002Marc J. Poulin During acclimatization to the hypoxia of altitude, the cerebral circulation is exposed to arterial hypoxia and hypocapnia, two stimuli with opposing influences on cerebral blood flow (CBF). In order to understand the resultant changes in CBF, this study examined the responses of CBF during a period of constant mild hypoxia both with and without concomitant regulation of arterial PCO2. Nine subjects were each exposed to two protocols in a purpose-built chamber: (1) 48 h of isocapnic hypoxia (Protocol I), where end-tidal PO2 (PET,O2) was held at 60 Torr and end-tidal PCO2 (PET,CO2) at the subject's resting value prior to experimentation; and (2) 48 h of poikilocapnic hypoxia (Protocol P), where PET,O2 was held at 60 Torr and PET,CO2 was uncontrolled. Transcranial Doppler ultrasound was used to assess CBF. At 24 h intervals during and after the hypoxic exposure CBF was measured and the sensitivity of CBF to acute variations in PO2 and PCO2 was determined. During Protocol P, PET,CO2 decreased by 13% (P < 0.001) and CBF decreased by 6% (P < 0.05), whereas during Protocol I, PET,CO2 and CBF remained unchanged. The sensitivity of CBF to acute variations in PO2 and PCO2 increased by 103% (P < 0.001) and 28% (P < 0.01), respectively, over the 48 h period of hypoxia. These changes did not differ between protocols. In conclusion, CBF decreases during mild poikilocapnic hypoxia, indicating that there is a predominant effect on CBF of the associated arterial hypocapnia. This fall occurs despite increases in the sensitivity of CBF to acute variations in PO2/PCO2 arising directly from the hypoxic exposure. [source] The effect of intracellular acidification on the relationship between cell volume and membrane potential in amphibian skeletal muscleTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005James A. Fraser The relationship between cell volume (Vc) and membrane potential (Em) in Rana temporaria striated muscle fibres was investigated under different conditions of intracellular acidification. Confocal microscope xz -scanning monitored the changes in Vc, whilst conventional KCl and pH-sensitive microelectrodes measured Em and intracellular pH (pHi), respectively. Applications of Ringer solutions with added NH4Cl induced rapid reductions in Vc that rapidly reversed upon their withdrawal. These could be directly attributed to the related alterations in extracellular tonicity. However: (1) a slower and persistent decrease in Vc followed the NH4Cl withdrawal, leaving Vc up to 10% below its resting value; (2) similar sustained decreases in resting Vc were produced by the addition and subsequent withdrawal of extracellular solutions in which NaCl was isosmotically replaced with NH4Cl; (3) the same manoeuvres also produced a marked intracellular acidification, that depended upon the duration of the preceding exposure to NH4Cl, of up to 0.53 ± 0.10 pH units; and (4) the corresponding reductions in Vc similarly increased with this exposure time. These reductions in Vc persisted and became more rapid with Cl, deprivation, thus excluding mechanisms involving either direct or indirect actions of pHi upon Cl, -dependent membrane transport. However they were abolished by the Na+,K+ -ATPase inhibitor ouabain. The Em changes that accompanied the addition and withdrawal of NH4+ conformed to a Nernst equation modified to include realistic NH4+ permeability terms, and thus the withdrawal of NH4+ restored Em to close to control values despite a persistent change in Vc. Finally these Em changes persisted and assumed faster kinetics with Cl, deprivation. The relative changes in Vc, Em and pHi were compared to predictions from the recent model of Fraser and Huang published in 2004 that related steady-state values of Vc and Em to the mean charge valency (zx) of intracellular membrane-impermeant anions, X,i. By assuming accepted values of intracellular buffering capacity (,i), intracellular acidification was shown to produce quantitatively predictable decreases in Vc. These findings thus provide experimental evidence that titration of the anionic zx by increased intracellular [H+] causes cellular volume decrease in the presence of normal Na+,K+ - ATPase activity, with Cl, -dependent membrane fluxes only influencing the kinetics of such changes. [source] Responses to handling and confinement stressors in juvenile great sturgeon Huso husoJOURNAL OF FISH BIOLOGY, Issue 4 2009B. Falahatkar The effects of acute stressors on physiological responses of juvenile great sturgeon or beluga Huso huso L. were investigated in two experiments. In the first experiment, fish were handled by placing them in containers at either low density (LD, one fish l,1) or high density (HD, four fish l,1) for 60 s. Concentrations of plasma cortisol, glucose and lactate were determined from blood collected at 0, 1, 3, 6 and 12 h after application of the stressor. Plasma cortisol concentrations increased after the disturbance in H. huso from both handling treatments, but changes were not significant. Plasma glucose rose significantly by 22·9 and 31·6% in LD and HD handling treatments, respectively, after 3 h. Significant increases in plasma lactate occurred within 1 h in both treatment groups, but that of the HD group was much higher. In the second experiment, fish were held at two different densities, LD (2 kg m,2 tank bottom surface area) and HD (7 kg m,2), for 8 weeks and then subjected to an aerial emersion handling stressor in a net for 60 s; blood samples were taken before handling (resting, 0 h) and at 1, 3, 6 and 9 h after handling. Plasma cortisol increased significantly in fish from the HD treatment from 8·8 ± 0·3 to 19·2 ± 2·4 ng ml,1 (mean ±s.e.) by 1 h after stress, but post-handling changes in the LD group were not significant. Significant increases in both plasma glucose and lactate were observed by 1 h in both treatment groups, with peak levels of plasma glucose evident at 3 h [69·4 ± 2·9 and 60·9 ± 1·7 mg dl,1 (mean ±s.e.) in LD and HD groups, respectively]. Plasma glucose levels were significantly higher in the LD group than in the HD group at 3 and 6 h. Post-handling haemoglobin content increased by 1 h and white blood cell numbers were reduced by 3 and 6 h in the HD treatment group compared with resting values, but changes in these blood features in the LD group were not significant. Acute handling did not affect haematocrit in either treatment. The results suggest that H. huso is relatively resistant to handling and confinement, and could tolerate normal hatchery practices associated with aquaculture. Because changes in cortisol concentrations were relatively low compared with those in most teleosts, glucose and lactate concentrations may be more useful as stress indicators in juvenile H. huso. This study also demonstrated that prior exposure to a chronic stressor, specifically high stocking density, could alter the physiological response to subsequent acute handling in H. huso. [source] Alterations in inorganic phosphate in mouse hindlimb muscles during limb disuse,NMR IN BIOMEDICINE, Issue 2 2008Neeti Pathare Abstract Muscle disuse induces a wide array of structural, biochemical, and neural adaptations in skeletal muscle, which can affect its function. We recently demonstrated in patients with an orthopedic injury that cast immobilization alters the resting Pi content of skeletal muscle, which may contribute to loss of specific force. The goal of this study was to determine the direct effect of disuse on the basal phosphate content in skeletal muscle in an animal model, avoiding the confounding effects of injury/surgery. 31P and 1H MRS data were acquired from the gastrocnemius muscle of young adult mice (C57BL6 female, n,=,8), at rest and during a reversible ischemia experiment, before and after 2 weeks of cast immobilization. Cast immobilization resulted in an increase in resting Pi content (75%; p,<,0.001) and the Pi to phosphocreatine (PCr) ratio (Pi/PCr; 80%, p,<,0.001). The resting concentrations of ATP, PCr and total creatine (PCr,+,creatine) and the intracellular pH were not significantly different after immobilization. During ischemia (30,min), PCr concentrations decreased to 54,±,2% and 52,±,6% of the resting values in pre-immobilized and immobilized muscles, respectively, but there were no detectable differences in the rates of Pi increase or PCr depletion (0.55,±,0.01,mM min,1 and 0.52,±,0.03,mM min,1 before and after immobilization, respectively; p,=,0.78). At the end of ischemia, immobilized muscles had a twofold higher phosphorylation potential ([ADP][Pi]/[ATP]) and intracellular buffering capacity (3.38,±,0.54 slykes vs 6.18,±,0.57 slykes). However, the rate of PCr resynthesis (kPCr) after ischemia, a measure of in vivo mitochondrial function, was significantly lower in the immobilized muscles (0.31,±,0.04,min,1) than in pre-immobilized muscles (0.43,±,0.04,min,1). In conclusion, our findings indicate that 2 weeks of cast immobilization, independent of injury-related alterations, leads to a significant increase in the resting Pi content of mouse skeletal muscle. The increase in Pi with muscle disuse has a significant effect on the cytosolic phosphorylation potential during transient ischemia and increases the intracellular buffering capacity of skeletal muscle. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||