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1.
Michael J. Webster Timothy P. Scheett Matthew R. Doyle Matthew Branz 《European journal of applied physiology and occupational physiology》1997,75(6):520-524
The purpose of this study was to investigate the effect of a thiamin derivative, thiamin tetrahydrofurfuryl disulfide (TTFD),
on oxygen uptake (˙VO2), lactate accumulation and cycling performance during exercise to exhaustion. Using a randomized, double-blind, cross-over
design with a 10-day washout between trials, 14 subjects ingested either 1 g · day−1 of TTFD or a placebo (PL) for 4 days. On day 3, subjects performed a progressive exercise test to exhaustion on a cycle ergometer
for the determination of ˙VO2submax, ˙VO2peak, lactate concentration ([La− ]), lactate threshold (ThLa) and heart rate ( f
c). On day 4, subjects performed a maximal 2000-m time trial on a cycle ergometer. A one-way analysis of variance (ANOVA) with
repeated measures was used to determine significant differences between trials. There were no significant differences detected
between trials for serial measures of ˙VO2submax, [La−] or f
c. Likewise, ˙VO2peak [PL 4.06 (0.19) TTFD 4.12 (0.19) l · min−1, P = 0.83], ThLa [PL 2.47 (0.17), TTFD 2.43 (0.16) l · min−1, P = 0.86] and 2000-m performance time [PL 204.5 (5.5), TTFD 200.9 (4.3) s, P = 0.61] were not significantly different between trials. The results of this study suggest that thiamin derivative supplementation
does not influence high-intensity exercise performance.
Accepted: 19 December 1996 相似文献
2.
Suzette R. Cooke Stewart R. Petersen H. Arthur Quinney 《European journal of applied physiology and occupational physiology》1997,75(6):512-519
Phosphorus magnetic resonance spectroscopy (31P-MRS) was used to investigate the influence of maximal aerobic power (˙VO
2max) on the recovery of human calf muscle from high-intensity exercise. The (˙VOO2max) of 21 males was measured during treadmill exercise and subjects were assigned to either a low-aerobic-power (LAP) group
(n = 10) or a high-aerobic-power (HAP) group (n = 11). Mean (SE) ˙VO 2max of the groups were 46.6 (1.1) and 64.4 (1.4) ml · kg−1 · min−1, respectively. A calf ergometry work capacity test was used to assign the same relative exercise intensity to each subject
for the MRS protocol. At least 48 h later, subjects performed the rest (4 min), exercise (2 min) and recovery (10 min) protocol
in a 1.5 T MRS scanner. The relative concentration of phosphocreatine (PCr) was measured throughout the protocol and intracellular
pH (pHi) was determined from the chemical shift between inorganic phospate (Pi) and PCr. End-exercise PCr levels were 27 (3.4) and 25 (3.5)% of resting levels for LAP and HAP respectively. Mean resting
pHi was 7.07 for both groups, and following exercise it fell to 6.45 (0.04) for HAP and 6.38 (0.04) for LAP. Analysis of data
using non-linear regression models showed no differences in the rate of either PCr or pHi recovery. The results suggest that ˙VO2max is a poor predictor of metabolic recovery rate from high-intensity exercise. Differences in recovery rate observed between
individuals with similar ˙VO2max imply that other factors influence recovery.
Accepted: 17 December 1996 相似文献
3.
H. Adelsberger J. Dudel 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1996,180(1):53-61
Whereas the inhibitory innervation of the deep extensor abdominal muscle in crayfish is mediated by a weakly acting common
inhibitor, the opener muscle exhibits a stronger inhibition. In the present study the most abundant γ-aminobutyric acid-activated
chloride channel on distal fibers of crayfish opener muscle was characterized by measuring the current responses after applying
pulses of γ-aminobutyric acid to outside-out patches. The results were compared to those obtained earlier with the chloride
channel on the deep extensor abdominal muscle of the same species. The double logarithmic plot of the dose-response relationship
had a slope of n
H = 2.2 in contrast to n
H = 5.3 for the channel on the deep extensor abdominal muscle. The rise time of the current response declined to 1 ms at a
γ-aminobutyric acid concentration of 50 mmol · l−1. With lower concentrations the rise time increased to a maximal value of 280 ms. No peak of the rise time at low γ-aminobutyric
acid concentrations, as observed for the channel on the deep extensor abdominal muscle, was obvious. The open and closed times
were similar to those of the channel of the deep extensor abdominal muscle. Different reaction schemes were discussed to describe
the kinetics of the chloride channel of the opener muscle.
Accepted: 12 August 1996 相似文献
4.
A. K. Tryba H. B. Hartman 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(3):215-221
Receptors monitoring muscle force innervate the opener muscle apodeme in the walking legs of the blue crab, Callinectes sapidus. Biocytin backfills reveal 9–15 bipolar neurons with somata as large as 60 μm positioned at the distal end of the apodeme.
Sensory endings insert into the apodeme and are in series with the opener muscle. The axons of these neurons form the opener
apodeme sensory nerve that merges with the most distal branch of the opener motor nerve. Recordings reveal that the receptors
are not spontaneously active nor do they respond to passive muscle stretch. Isometric muscle contraction evoked by stimulating
the opener excitor motor neuron is the adequate stimulus for receptor firing. Most significant is the finding that during
contraction, over a wide range of forces, the firing rate of individual receptors closely parallels the rate of change of
isometric force. The peak instantaneous frequency typically occurs at the force derivative maximum, but not at maximum force
development. Thus, receptors of the opener apodeme sensory nerve more closely monitor changes in isometric force rather than
the total force achieved.
Accepted: 20 September 1996 相似文献
5.
O. Buttelli H. Vandewalle J. C. Jouanin D. Seck H. Monod 《European journal of applied physiology and occupational physiology》1997,75(6):499-503
The kinetics of the torque-velocity (T-ω) relationship after aerobic exercise was studied to assess the effect of fatigue on the contractile properties of muscle.
A group of 13 subjects exercised until fatigued on a cycle ergometer, at an intensity which corresponded to 60% of their maximal
aerobic power for 50 min (MAP60%); ten subjects exercised until fatigued at 80% of their maximal aerobic power for 15 min
(MAP80%). Of the subjects 7 exercised at both intensities with at least a 1-week interval between sessions. Pedalling rate
was set at 60 rpm. The T-ω relationship was determined from the velocity data collected during all-out sprints against a 19 N · m braking torque on
the same ergometer, according to a method proposed previously. Maximal theoretical velocity (ω0) and maximal theoretical torque (T
0) were estimated by extrapolation of the linear T-ω relationship. Maximal power (P
max) was calculated from the values of T
0 and ω0 (P
max = 0.25 ω0 T
0). The T-ω relationships were determined before, immediately after and 5 and 10 min after the aerobic exercise. The kinetics of ω0, T
0 and P
max was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal
muscle strength and maximal power). Immediately after exercise at MAP60% a 7.8% decrease in T
0 and 8.8% decrease in P
max was seen while the decrease in ω0 was nonsignificant, which suggested that P
max decreased in the main because of a loss in maximal muscle strength. In contrast, MAP80% induced a 8.1% decrease in ω0 and 12.8% decrease in P
max while the decrease in T
0 was nonsignificant, which suggested that the main cause of the decrease in P
max was probably a slowing of maximal shortening velocity. The short recovery time of the T-ω relationship suggests that the causes of the decrease of torque and velocity are processes which recover rapidly.
Accepted: 25 November 1996 相似文献
6.
S. Egginton 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):129-134
The physiological responses to forced exercise were studied in yellowbelly and marbled rockcod (Notothenia coriiceps and N. rossii), and the haemoglobinless icefish (Chaenocephalus aceratus), from blood samples obtained via indwelling catheters. The maximal exertion tolerable by N. coriiceps was 3–5 min, although N. rossii was not fully exhausted by this effort, and it proved difficult to elicit sustained maximal activity in C. aceratus. Arterial O2 tension reflected the relative degree of exhaustion, showing a significant fall in the case of N. coriiceps, little change in N. rossii, and even a rise in C. aceratus as a result of hyperventilation. Such changes in the red-blooded species were not caused by altered O2 carrying capacity, as there was no change in haematocrit. In Notothenia spp. the decrease in arterial pH was better correlated with a rise in arterial CO2 tension than with blood lactate concentration, which is reflected in a modest net metabolic acid load. In contrast, the icefish
showed an attenuated hypercapnia and a more pronounced lactacidosis, but an insignificant net metabolic acid load. Disturbance
in ionoregulation following exercise was limited to an elevated [Cl−] in Notothenia, while circulating catecholamine levels remained unusually low in all specimens. The response to stress appears to reflect
lifestyle and/or endemic speciation, rather than specific adaptations to the stenothermal environment.
Accepted: 9 August 1996 相似文献
7.
G. Gaus M. Casaretto L. Kass 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(2):137-142
Retinal responses of the Limulus lateral eyes to light are greater at night than during the day. A circadian clock in the brain of the horseshoe crab controls
these rhythmic changes of light sensitivity. The increase in sensitivity (as measured by the amplitude of the electroretinogram)
is mediated at least in part by octopamine that is released from efferent axons terminating in the visual cells. Earlier studies
indicate that certain factors in Limulus hemolymph can act in conjunction with octopamine. More recently, five neuropeptides (LP1-LP4 and Lip-HP) had been isolated
from acetone extracts of the Limulus central nervous system using HPLC fractionation and radioimmunoassay with antisera against FMRFamide-like peptides for detection.
Presently, we have injected into the Limulus lateral eye these five peptides and observed changes in retinal sensitivity. Injection during daytime had no immediate effect
on that daytime electroretinogram but decreased the electroretinogram amplitude for the entire subsequent night (12 h). However,
upon injection at night, we observed an immediate but only transitory decrease in electroretinogram amplitude for about 1
h without effect on the subsequent daytime electroretinogram. We suggest that the peptides act antagonistically to octopamine
and are highly dependent upon the activity state of the efferent nerve terminals.
Accepted: 25 August 1996 相似文献
8.
B. Melin C. Jimenez G. Savourey J. Bittel J. M. Cottet-Emard J. M. Pequignot A. M. Allevard C. Gharib 《European journal of applied physiology and occupational physiology》1997,76(4):320-327
The effects of hydromineral hormones and catecholamines on renal concentrating ability at different hydration states were
examined in five male volunteers while they performed three trials. Each of these trials comprised a 60-min exercise bout
on a treadmill (at 50% of maximal oxygen uptake) in a warm environment (dry bulb temperature, 35°C; relative humidity, 20–30%).
In one session, subjects were euhydrated before exercise (C). In the two other sessions, after thermal dehydration (loss of
3% body mass) which markedly reduced plasma volume (PV) and increased plasma osmolality (osmpl), the subjects exercised either not rehydrated (Dh) or rehydrated (Rh) by drinking 600 ml of mineral water before and 40 min
after the onset of exercise. During exercise in the Dh compared to C state, plasma renin, aldosterone, arginine vasopressin
(AVP), noradrenaline and adrenaline concentrations were increased (P < 0.05). A reduction in creatinine clearance and urine flow was also observed (P < 0.05) together with a decrease in urine osmolality, osmolar clearance and sodium excretion, while free water clearance
increased (P < 0.05). However, compared to Dh, Rh partially restored PV and osmpl and induced a marked reduction in the time courses of both the plasma AVP and catecholamine responses (P < 0.05). Values for renal water and electrolyte excretion were intermediate between those of Dh and C. Plasma atrial natriuretic
peptide presented similar changes whatever the hydration state. These results demonstrate that during moderate exercise in
the heat, renal concentrating ability is paradoxically reduced by prior dehydration in spite of high plasma AVP levels, and
might be the result of marked activation of the sympatho-adrenal system. Rehydration, by reducing this activation, could partially
restore the renal concentrating ability despite the lowered plasma AVP.
Accepted: 23 April 1997 相似文献
9.
S. J. Brown R. B. Child S. H. Day A. E. Donnelly 《European journal of applied physiology and occupational physiology》1997,75(4):369-374
Indirect indices of exercise-induced human skeletal muscle damage and connective tissue breakdown were studied following
a single bout of voluntary eccentric muscle contractions. Subjects (six female, two male), mean (SD) age 22 (2) years performed
a bout of 50 maximum voluntary eccentric contractions of the knee extensors of a single leg. The eccentric exercise protocol
induced muscle soreness (P < 0.05 Wilcoxon test), chronic force loss, and a decline in the 20:100 Hz percutaneous electrical myostimulation force ratio
[P < 0.01, repeated measures analysis of variance (ANOVA)]. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities
were elevated (P < 0.01, repeated measures ANOVA) following the bout. The mean (SD) CK and LDH levels recorded 3 days post-exercise were 2815
(4144) IU · l–1 and 375 (198) IU · l–1, respectively. Serum alkaline phosphatase activity showed no changes throughout the study, and a non-significant increase
(P = 0.058, repeated measures ANOVA) in pyridinoline was recorded following the bout. Urinary hydroxyproline (HP) and hydroxylysine
(HL) excretion, expressed in terms of creatinine (Cr) concentration, increased after exercise (P < 0.05 and P < 0.01, respectively, repeated measures ANOVA). An increased HP:Cr was recorded 2 days post-exercise and HL:Cr was increased
above baseline on days 2, 5, and 9 post-exercise. This indirect evidence of exercise-induced muscle damage suggests that myofibre
disruption was caused by the eccentric muscle contractions. Elevated urine concentrations of indirect indices of collagen
breakdown following eccentric muscle contractions suggests an increased breakdown of connective tissue, possibly due to a
localised inflammatory response.
Accepted: 9 October 1996 相似文献
10.
The effect of light environment, leaf area, and stored carbohydrates on inflorescence production by a rain forest understory palm 总被引:2,自引:0,他引:2
Saul A. Cunningham 《Oecologia》1997,111(1):36-44
Variation in flowering by long-lived plants may be correlated with current resource availability. If, however, there are
trade-offs between current and future reproduction, or between reproduction and storage or growth, then understanding variation
requires a whole-plant, longer-term perspective. Inflorescence production by Calyptrogyne ghiesbreghtiana Linden ex. H. Wendl., an understory palm, was studied over 3 years. Annual inflorescence production varied greatly and was
correlated with variation in plant size and light environment. There was no trade-off between past inflorescence production
and the frequency of future inflorescence production. On the contrary, individuals that produced more inflorescences than
predicted from their size and light environment tended to continue to do so in subsequent years also. I manipulated the resource
environment of a subset of plants by removal of leaves and/or reproductive spikes. Leaf removal suppressed inflorescence production
for the following 2 years, but spike removal had no effect. One year after leaf removal stored reserves were, on average,
back to pre-treatment levels. There was, however, a negative effect of recent inflorescence production on storage. Plants
with higher levels of storage had higher inflorescence production in the next 75 days. In C. ghiesbreghtiana the resource cost of reproduction is apparent in short-term variation in stored reserves. In contrast, annual inflorescence
production does not follow a trade-off pattern between successive years, but consistently reflects both plant size and the
light environment.
Received: 20 October 1996 / Accepted: 25 January 1997 相似文献
11.
Ralph Beneke Katharina Meyer 《European journal of applied physiology and occupational physiology》1997,75(3):246-251
The effect of a 3-week exercise programme on performance and economy of walking was analysed in 16 male patients with chronic
heart failure [mean age 51.8 (SD 6.9) years, height 174.9 (SD 6.3) cm, body mass 75.3 (SD 11.5) kg, ejection fraction 20.8
(SD 5.0)%]. They were submitted to a cardiopulmonary exercise test on a cycle ergometer and a 6-min walking test on a treadmill
before and after the period of exercise training. The training programme consisted of interval cycle (five times a week for
15 min), and treadmill ergometer training (three times a week for 10 min) at approximately 70% cycling peak oxygen uptake
(O2peak) and supplementary exercises (three times a week for 20 min). Compared to the pre values cycling O2peak [11.9 (SD 2.9) vs 14.0 (SD 2.3) ml · kg–1 · min–1], maximal self paced walking speed [0.68 (SD 0.33) vs 1.16 (SD 0.30) m · s–1], and net walking power [2.16 (SD 0.89) vs 2.73 (SD 0.91) W · kg–1] had increased (P < 0.01) while net energy cost [3.31 (SD 0.66) vs 2.33 (SD 0.38) J · kg–1 · m–1] had decreased (P < 0.001) after the training period. Approximately 42% of the increase of walking speed resulted from a higher walking power
output, whereas approximately 58% corresponded to a positive effect on walking economy. The improvement in walking economy
was a function of an increase in walking velocity itself and a result of a more efficient walking technique. These results
would indicate that in patients with marked exercise intolerance, adequate exercise training programmes could contribute to
favourable metabolic changes with positive effects on the economy of motion.
Accepted: 29 August 1996 相似文献
12.
Gerhard Krumschnabel Christina Biasi Pablo J. Schwarzbaum Wolfgang Wieser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):280-286
Short- and long-term effects of temperature on ion flux and energy turnover were studied in hepatocytes from thermally acclimated
trout and roach. In trout hepatocytes K+ efflux was insensitive towards acute exposure to low temperature but was downregulated during cold acclimation of the fish
so as to balance the uncompensated decreased K+(Rb+) uptake of the cells. In contrast, both K+(Rb+) uptake and K+ efflux of roach hepatocytes were temperature sensitive in the short term. These acute effects, however, were offset during
cold acclimation by a near perfect compensation of both fluxes leading to re-establishment of ion flux homeostasis at the
original level. Our findings, based on a new method permitting the simultaneous monitoring of K+ efflux and uptake in the same cell population, provide experimental verification of two of the three possible strategies,
recently discussed by Cossins et al. (1995), by which the ionic steady state of fish cells may adjust to acute and chronic
temperature change. By comparing hepatocytes from two groups of trout, one kept on a maintenance diet (ration I), the other
fed ad libitum (ration II), we discovered striking effects of nutritional state on the absolute levels as well as on the temperature relationships
of K+ uptake and protein synthetic activity. Both of these functions in the hepatocytes increased in the ration II fed as compared
to the ration I fed trouts, but the increase of protein synthetic activity was greater and more uniform at the three experimental
temperatures than that of K+ uptake. Moreover, protein synthetic activity proved to be considerably more temperature sensitive than K+ uptake and, in contrast to the latter, showed a compensatory response after cold acclimation.
Accepted: 16 December 1996 相似文献
13.
David Ben-Sira Michael Sagiv 《European journal of applied physiology and occupational physiology》1997,75(6):549-553
The effect of gender on left ventricular systolic function and exercise haemodynamics in healthy young subjects was studied
during 30-s all-out sudden strenuous dynamic exercise. A group of 22 men [19.3 (SD 1) years] 20 women [19.1 (SD 1) years]
volunteered to participate in this study. Two-dimensional direct M-mode and Doppler echocardiograph studies were performed
with the subject in the sitting position. The Doppler examination of flow was located with continuous-wave, interrogating
ascending aorta measurements. The subjects completed the study without showing any electrocardiograph abnormalities. An interaction
effect with stroke volume (P < 0.05) was characterized by a decrease in the men and an increase of stroke volume in the women. Cardiac output rose significantly
(P < 0.05) up to 14.5 (SD 6) l · min−1) for the men and 12.1 (SD 4) l · min−1 for the women compared to the rest values [5.8 (SD 0.4) and 4.7 (SD 0.5) l · min−1, respectively]. Flow velocity integral and acceleration time differed significantly between the two groups at rest (P < 0.05). During exercise these differences showed an interaction effect (P < 0.05). These results would indicate that normal men and women respond to sudden strenuous exercise by reducing their left
ventricular systolic function, with a significantly greater decrease in women (P < 0.05). The gender differences in the haemodynamic responses during the present study, may, as suggested by others, be attributable
to differences in energy metabolism. In addition, changes in Doppler parameters of aortic flow, haemodynamics and blood pressure
responses during sudden strenuous exercise differed markedly from those seen before with endurance exercise.
Accepted: 8 January 1997 相似文献
14.
John A. Hawley Garry S. Palmer Timothy D. Noakes 《European journal of applied physiology and occupational physiology》1997,75(5):407-412
This study compared the effects of supplementing the normal diets of six trained cyclists [maximal oxygen uptake O2max) 4.5 (0.36)l · min−1; values are mean (SD)] with additional carbohydrate (CHO) on muscle glycogen utilisation during a 1-h cycle time-trial (TT).
Using a randomised crossover design, subjects consumed either their normal diet (NORM) for 3 days, which consisted of 426
(137) g · day−1 CHO [5.9 (1.4) g · kg−1 body mass (BM)], or additional CHO (SUPP) to increase their intake to 661 (76) g · day−1 [9.3 (0.7) g · kg−1 BM]. The SUPP diet elevated muscle glycogen content from 459 (83) to 565 (62) mmol · kg−1 dry weight (d.w.) (P < 0.05). However, despite the increased pre-exercise muscle glycogen stores, there was no difference in the distance cycled
during the TT [40.41 (1.44) vs 40.18 (1.76) km for NORM and SUPP, respectively]. With NORM, muscle glycogen declined from
459 (83) to 175 (64) mmol · kg−1 d.w., whereas with SUPP the corresponding values were 565 (62) and 292 (113) mmol · kg−1 d.w. Accordingly, both muscle glycogen utilisation [277 (64) vs 273 (114) mmol · kg−1 d.w.] and total CHO oxidation [169 (20) vs 165 (30) g · h−1 for NORM and SUPP, respectively] were similar. Neither were there any differences in plasma glucose or lactate concentrations
during the two experimental trials. Plasma glucose concentration averaged 5.5 (0.5) and 5.6 (0.6) mmol · l−1, while plasma lactate concentration averaged 4.4 (1.9) and 4.4 (2.3) mmol · l−1 for NORM and SUPP, respectively. The results of this study show that when well-trained subjects increase the CHO content
of their diet for 3 days from 6 to 9 g · kg−1 BM there is only a modest increase in muscle glycogen content. Since supplementary CHO did not improve TT performance, we
conclude that additional CHO provides no benefit to performance for athletes who compete in intense, continuous events lasting
1 h. Furthermore, the substantial muscle CHO reserves observed at the termination of exercise indicate that whole-muscle glycogen
depletion does not determine fatigue at this exercise intensity and duration.
Accepted: 25 November 1996 相似文献
15.
This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with
or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment
(Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O2max = 55.5 (4.4 SD) ml kg−1 min−1]. The RE was measured at 3 m s−1 [65 (6)% V˙O2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined
from prior tests, to maintain body mass (group mean = 17.4 ml min−1). The V˙O2 during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase
in V˙O2 from RE1 to RE2 ranged from 3.4 to 4.7 ml kg−1 min−1 across treatments. In conclusion, the deterioration in RE at 3 m s−1 (65% V˙O2max) after 60 min of running at 80% V˙O2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or
electrolytes, in both a thermoneutral and in a hot, humid environment.
Accepted: 30 October 1997 相似文献
16.
The Pseudomonas aeruginosa leuB gene, encoding 3-isopropylmalate dehydrogenase, was identified upstream of asd, encoding aspartate-β-semialdehyde dehydrogenase. Genetic analysis indicated that leuB is identical to the previously mapped gene defined by the leu-10 allele. The chromosomal leuB locus was inactivated by gene replacement. The insertions had no adverse effect on expression of the downstream asd gene but resulted in leucine auxotrophy. The leuB gene encodes a protein containing 360 amino acids (with a molecular weight of 39153), which was expressed in Escherichia coli as a M, 42000 protein. The results suggested that, in contrast to the situation in other bacteria (E. coli, Salmonella typhimurium and Bacillus subtilis) the P. aeruginosa leuB gene is physically separated from the genes encoding the other enzymes of the isopropylmalate pathway.
Received: 15 August 1996 / Accepted: 23 October 1996 相似文献
17.
Hilde Spielvogel Armando Rodriguez Brigitte Sempore Esperanza Caceres J.-M. Cottet-Emard Laurent Guillon R. Favier 《European journal of applied physiology and occupational physiology》1997,75(5):400-406
The present study was undertaken to determine the haematological and cardiovascular status, at rest and during prolonged
(1 h) submaximal exercise (approximately 70% of peak oxygen uptake) in a group (n = 12) of chronic coca users after chewing approximately 50 g of coca leaves. The results were compared to those obtained
in a group (n = 12) of nonchewers. At rest, coca chewing was accompanied by a significant increase in heart rate [from 60 (SEM 4) TO 76 (SEM 3)
beats · min−1], in haematocrit [from 53.2 (SEM 1.2) to 55.6 (SEM 1.1)%] in haemoglobin concentration, and plasma noradrenaline concentration
[from 2.8 (SEM 0.4) to 5.0 (SEM 0.5) μmol · l−1]. It was calculated that coca chewing for 1 h resulted in a significant decrease in blood [−4.3 (SEM 2.2)%] and plasma [−8.7 (SEM 1.2)%]
volume. During submaximal exercise, coca chewers displayed a significantly higher heart rate and mean arterial blood pressure.
The exercise-induced haemoconcentration was blunted in coca chewers compared to nonchewers. It was concluded that the coca-induced
fluid shift observed at rest in these coca chewers was not cumulative with that of exercise, and that the hypovolaemia induced
by coca chewing at rest compromised circulatory adjustments during exercise.
Accepted: 29 October 1996 相似文献
18.
Jonas Dahl 《Oecologia》1998,117(1-2):217-226
I assessed the impact of both vertebrate and invertebrate predators on a lotic benthic community in a 1-month-long experiment,
using enclosures containing cobble/gravel bottoms, with large-mesh netting that allowed invertebrates to drift freely. Brown
trout (Salmo trutta) and leeches (Erpobdella octoculata) were used as predators and four treatments were tested: a predator-free control, leeches only, trout only, and leeches and
trout together. A density of 26.7 leeches/m2 (20 leeches/enclosure) and 1.3 trout/m2 (one trout per enclosure) was stocked into the enclosures. The total biomass of invertebrate prey was significantly lower
in the trout and trout plus leech treatments than in the leech and control treatments, which were due to strong negative effects
of trout on Gammarus. On the individual prey taxon level, both trout and leeches affected the abundance of Asellus
,
Baetis and Ephemerella, whereas the abundance of Gammarus was only affected by trout, and the abundance of Orthocladiinae and Limnephilidae was only affected by leeches. In the treatment
with trout and leeches together, the abundance of Ephemerella and Baetis was higher than when trout or leeches were alone, which was probably due to predator interactions. Leeches and trout had
no effects on prey immigration but did affect per capita emigration rates. Both trout and leeches indirectly increased periphyton
biomass in enclosures, probably due to their strong effects on grazers. Both trout and leeches were size-selective predators,
with trout selecting large prey, and leeches selecting small prey. Size-selective predation by trout and leeches affected
the size structure of five commonly consumed prey taxa. Trout produced prey populations of small sizes owing to consumption
of large prey as well as increased emigration out of enclosures by these large prey. Leech predation produced prey assemblages
of larger size owing to consumption and increased emigration of small prey. These results suggest that in lotic habits, predatory
invertebrates can be as strong interactors as vertebrate predators.
Received: 23 June 1997 / Accepted: 4 May 1998 相似文献
19.
D. J. Hosken P. C. Withers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):71-80
The thermal and metabolic physiology of Chalinolobus gouldii, an Australian vespertilionid bat, was studied in the laboratory using flow-through respirometry. Chalinolobus gouldii exhibits a clear pattern of euthermic thermoregulation, typical of endotherms with respect to body temperature and rate of
oxygen consumption. The basal metabolic rate of euthermic Chalinolobus gouldii is approximately 86% of that predicted for a 17.5-g mammal and falls into the range of mass-specific basal metabolic rates
ascribed to vespertilionid bats. However, like most vespertilionid bats, Chalinolobus gouldii displays extreme thermolability. It is able to enter into torpor and spontaneously arouse at ambient temperatures as low
as 5 °C. Torpid bats thermoconform at moderate ambient temperature, with body temperature ≈ ambient temperature, and have
a low rate of oxygen consumption determined primarily by Q
10 effects. At low ambient temperature (< 10 °C), torpid C. gouldii begin to regulate their body temperature by increased metabolic heat production; they tend to maintain a higher body temperature
at low ambient temperature than do many northern hemisphere hibernating bats. Use of torpor leads to significant energy savings.
The evaporative water loss of euthermic bats is relatively high, which seems unusual for a bat whose range includes extremely
arid areas of Australia, and is reduced during torpor. The thermal conductance of euthermic C. gouldii is less than that predicted for a mammal of its size. The thermal conductance is considerably lower for torpid bats at intermediate
body temperature and ambient temperature, but increases to euthermic values for torpid bats when thermoregulating at low ambient
temperature.
Accepted: 22 August 1996 相似文献
20.
In this study we used pinfish (Lagodon rhomboides) in field experiments to examine linkages between intertidal saltmarsh and adjacent subtidal habitats. Pinfish are more
than twice as abundant in intertidal marshes adjacent to seagrass beds than in those adjacent to the unvegetated subtidal
bottom. Movement of pinfish between the marsh edge and the adjacent subtidal habitat was greater for fish captured in areas
with both intertidal and subtidal vegetation than in those with intertidal vegetation and adjacent unvegetated mudflats. This
movement provides an important link between habitats, allowing transfer of marsh-derived secondary production to subtidal
seagrass beds and vice versa. Pinfish held in enclosures with both intertidal and subtidal vegetation were, on average, approximately
90% heavier than fish held in enclosures with intertidal vegetation and unvegetated subtidal bottom. Because saltmarshes and
seagrass beds contribute to the production of living marine resources, active measures are being taken to preserve and restore
these habitats. The results from this study have direct application to decisions concerning site selection and optimal spatial
proximity of saltmarsh and seagrass habitats in the planning of restoration and mitigation projects. To maximize secondary
production and utilization of intertidal marshes, managers may opt to restore and/or preserve marshes adjacent to subtidal
seagrass beds.
Received: 31 May 1996 / Accepted: 23 October 1996 相似文献