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1.
High groundwater nitrate concentrations inhibit eutrophication of sulphate-rich freshwater wetlands 总被引:2,自引:0,他引:2
E.C.H.E.T. Lucassen A.J.P. Smolders A.L. van der Salm J.G.M. Roelofs 《Biogeochemistry》2004,67(2):249-267
During the last 60 years, pollution of the groundwater with
has greatly increased in many parts of Europe, as a consequence of excessive use of manure and synthetic fertilisers. Monitoring of groundwater-fed wetlands indicated that sediments with high
concentrations had the lowest Fe and
concentrations in the pore water. A comparison of two restored open water fens, differing in
supply via the groundwater, indicated that the redox potential and the sulphate (
) reduction rate were lower when the groundwater contained not only
but also high
concentrations. The lower
reduction rates in the
-rich open water fen were associated with lower
concentrations and the presence of plant species characteristic of clear water. In contrast, the higher
reduction rates in the
-poor open water fen were associated with very high
concentrations and massive development of plant species characteristic of eutrophic environments. Investigations at
-rich seepage sites in black alder carrs, showed that high
concentrations in the pore water caused chlorosis in the alder carr vegetation, due to lower availability of Fe in the pore water and less Fe uptake by the plants. Experimental desiccation of sediments proved that the
-rich seepage sites contained no oxidisable FeS
x
, contrary to
-poor locations, which became acidified and mobilised extremely high amounts of
due to FeS
x
oxidation. A laboratory experiment showed that
addition to sediments led to reduced releases of Fe,
and S2–, very likely due to the oxidation of reduced Fe and S compounds. Overall, the results confirmed that
is an energetically more favourable electron acceptor in anaerobic sediments than Fe and
, and that high
loads function as a redox buffer, preventing reduction of Fe and
. Limited
reduction prevents S2– -mediated mobilisation of
from Fe-
complexes. At a higher redox potential, reduced Fe, including FeS
x
, was oxidised, increasing the content of Fe(III) capable of binding
. This prevented increased
availability and the concomitant massive development of plant species characteristic of eutrophic environments. 相似文献
2.
Douglas A. Burns 《Biogeochemistry》1998,40(1):73-96
Models of the effects of atmosphericN deposition in forested watersheds have notadequately accounted for the effects of aquatic andnear-stream processes on the concentrations and loadsof NO
in surface waters. This studycompared the relative effects of aquatic andnear-stream processes with those from the terrestrialecosystem on the retention and transport ofNO
in two contrasting stream reaches ofthe Neversink River, a forested watershed in theCatskill Mountains of New York that receives among thehighest load of atmospheric N deposition in thenortheastern United States. Stream water samples werecollected every two hours and ground-water andtributary samples were collected daily at base flowconditions during four 48-hour periods from April toOctober 1992, and NO
mass balances werecalculated for each site. Results indicated diurnalvariations in stream NO
concentrations inboth reaches during all four sampling periods; this isconsistent with uptake of NO
byphotoautotrophs during daylight hours. Mass-balanceresults revealed significant stream reach losses ofNO
at both sites during all samplingperiods. The diurnal variations in NO
concentrations and the retention of NO
relative to terrestrial contributions to the streamreaches were greater downstream than upstream becausephysical factors such as the head gradients ofinflowing ground water and the organic matter contentof sediment are more favorable to uptake anddenitrification downstream. The mass retention ofNO
increased as the mean 48-hr streamdischarge increased at each site, indicating that theresponsible processes are dependent onNO
supply. Low stream temperatures duringthe April sampling period, however, probably reducedthe rate of retention processes, resulting in smallerlosses of NO
than predicted from streamdischarge alone. Water samples collected from thestream, the hyporheic zone, and the alluvial groundwater at sites in both reaches indicated that the neteffect of hyporheic processes on downstreamNO
transport ranged from conservativemixing to complete removal by denitrification. Therelative effects of biological uptake anddenitrification as retention mechanisms could not bequantified, but the results indicate that bothprocesses are significant. These results generallyconfirm that aquatic and near-stream processes causesignificant losses of NO
in the NeversinkRiver, and that the losses by these processes atdownstream locations can exceed the NO
contributions to the stream from the terrestrialenvironment during summer and fall base-flowconditions. Failure to consider these aquatic andnear-stream processes in models of watershed responseto atmospheric N deposition could result inunderestimates of the amount of NO
leaching from forested ecosystems and to an inabilityto unequivocally relate geographic differences inNO
concentrations of stream waters tocorresponding differences in terrestrial processes. 相似文献
3.
Intermittent drainage of rice fields isdiscussed as an option to mitigate emission ofCH4, an important greenhouse gas. HoweverN2O, a potentially more effective greenhouse gas,may be emitted during the aeration phase. Therefore,the metabolism of NO, N2O, NH
,NO
and NO
and the kinetics ofCH4 oxidation were measured after aeration ofmethanogenic rice field soil. Before aeration, thesoil contained NH
in relatively highconcentrations (about 4 mM), while NO
andNO
were almost undetectable. Immediatelyafter aeration both NO and N2O were produced withrates of about 15 pmol h-1 gdw-1 and 5 pmolh-1 gdw-1, respectively. Simultaneously,NH
decreased while NO
accumulated. Later on, NO
was depletedwhile NO
concentrations increased.Characteristic phases of nitrogen turnover wereassociated with the activities of ammonium oxidizers,nitrite oxidizers and denitrifiers. Oxidation ofNH
and production of NO and N2O wereinhibited by 10 Pa acetylene demonstrating thatnitrification was obligatory for the initiation ofnitrogen turnover and production of NO and N2O.Ammonium oxidation was not limited by the availableNH
and thus, concomittant production of NOand N2O was not stimulated by addition ofNH
. However, addition of NO
stimulated production of NO and N2O in bothanoxic and aerated rice soil slurries. In this case,10 Pa acetylene did not inhibit the production of NOand N2O demonstrating that it was due todenitrification which was obviously limited by theavailability of NO
. In the aerated soilslurries CH4 was only oxidized if present atelevated concentrations >50 ppmv CH4). Atatmospheric CH4 concentrations (1.7 ppmv)CH4 was not consumed, but was even slightly produced.CH4 oxidation activity increased afterpreincubation at 20% CH4, and then CH4was also oxidized at atmospheric concentrations. CH4oxidation kinetics exhibited sigmoid characteristicsat low CH4 concentrations presumably because ofinhibition of CH4 oxidation by NH
. 相似文献
4.
Pierre Dejours Jean-Paul Truchot 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1988,158(3):387-391
Summary In the intertidal shore crab,Carcinus maenas, pH and
values of the prebranchial venous hemolymph,
and
, the PO2 values of the arterialized cardiac hemolymph,
, were measured, and the ventilatory activity was assessed by measuring the hydrostatic pressures at the exits of the epibranchial cavities, under four environmental conditions: normoxic water, normoxic air, hypoxic gas, hyperoxic gas.In the crab breathing normoxic air,
was lower and
higher than in animals breathing normoxic water. With the switch to hypoxic gas, ventilation increased and
and
decreased. With the switch to hyperoxic gas, ventilation decreased,
and
increased and
decreased.Thus these crabs breathing air were not as well oxygenated as when breathing air-equilibrated water, and because of their low
, they were relatively hypervetilating and hypocapnic compared to air-breathing vertebrates. Hyperoxic breathing, increasing
and reducing ventilatory drive, led to increased
. Conversely,
was reduced by hypoxic breathing. These observations suggest that the gas exchanger of intertidal crabs is not as successfully designed for air breathing as that of land-colonizing insects and air-breathing vertebrates. 相似文献
5.
Øivind Andersen Johan B. Steen 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1986,156(6):823-828
Summary Nest humidity (
) under an incubating bantam hen was measured at ambient
ranging from 1.3 to 25.0 mmHg. Weight loss of eggs was recorded in clutches of varying size. Nest
and ambient
were also measured in wild incubating willow ptarmigan nests in dry and wet habitats.Nest
increased linearly with ambient
in a way predictable on the assumption that the water vapour conductance (
) of brood patch skin, plumage and eggs were constant and independent of ambient
. Nest
was also dependent of clutch size. Egg dehydration was quantitatively predicted from measured values and the laws of diffusion.Our findings confirm earlier conclusions that the adult bird does not actively regulate nest
at varying ambient
. Birds can presumably achieve appropriate egg dehydration by a strategy combining nest site, nest construction, egg shell conductance and incubation behaviour which meets the requirements of their breeding climate.Abbreviations
water vapur pressure
-
water vapur conductance
-
water flux 相似文献
6.
A simple linear relationship between the J
coupling constant and the linewidth (1/2) of in-phase NMR peaks has been identified. This relationship permits the rapid and accurate determination of polypeptide J
coupling constants from a simple inspection of amide cross peaks in homonuclear 1H TOCSY or 1H NOESY spectra. By using the appropriate set of processing parameters we show that J
= 0.5(1/2) – MW/5000 + 1.8 for TOCSY spectra and J
= 0.6(1/2) – MW/5000 – 0.9 for NOESY spectra, where 1/2 is the half-height linewidth in Hz and MW is the molecular weight of the protein in Da. The simplicity of this relationship, combined with the ease with which 1/2 measurements can be made, means that J
coupling constants can now be rapidly determined (up to 100 measurements in less than 30 min) without the need for any complex curve-fitting algorithms. Tests on 11 different polypeptides involving more than 650 separate J
measurements have shown that this method yields coupling constants with an rmsd error (relative to X-ray data) of less than 0.9 Hz. Furthermore, the correlation coefficient between the predicted NMR coupling constants and those derived from high-resolution X-ray crystal structures is typically better than 0.89. These simple linear relationships have been found to be valid for peptides as small as 1 kDa to proteins as large as 20 kDa. Despite the method's simplicity, these results are comparable to the accuracy and precision of the best techniques published to date. 相似文献
7.
R. A. Cole 《Entomologia Experimentalis et Applicata》1997,85(2):121-133
This paper describes an experiment to investigate the relative importance of glucosinolates and the availability of free amino acids in the phloem to the feeding behaviour and development of the specialist brassica aphid, Brevicoryne brassicae (L) (cabbage aphid) and the generalist, Myzus persicae, (Sultzer) (peach potato aphid). Aphid development was determined on brassica species and cultivated brassica varieties. Analysis of individual glucosinolates in the wild brassica species identified significant differences in their profiles and in their concentrations present in freeze dried leaves. Multiple regression analysis showed a significant correlation (
) between the intrinsic rate of increase of B. brassicae and glucosinolate concentrations; four glucosinolates, 2-OH-3-butenyl, and 2-propenylglucosinolate, 3-methoxyindolyl and 4-pentenylglucosinolates accounted for 79% of the variation. The intrinsic rate of increase of M. persicae was less correlated, though still significant (
); 3-indolyglucosinolate and 3-butenylglucosinolate accounted for 47% of the variation. Regression analysis also showed a correlation between phloem amino acid concentrations and the intrinsic rate of increase of B. brassicae (
) but not of M. persicae. The concentration of the important amino acids tyrosine, alanine, leucine and glutamic acid, accounted for 43% of the variation in intrinsic rate of increase. Leaf water potential of the Brassica species showed no relationship with the intrinsic rate of increase of either B. brassicae or M. persicae. 相似文献
8.
Boniface S. Moses 《Environmental Biology of Fishes》2001,61(1):99-109
This paper investigates the relationship between the hydroclimatic parameters (rainfall and flood index) and the catch, stock abundance and recruitment of the catfish, Chrysichthys nigrodigitatus (Bagridae) and the bonga, Ethmalosa fimbriata (Clupeidae) of southeastern Nigeria's inshore waters. For C. nigrodigitatus, most peaks in the mean biomass
and recruitment
curves occurred during the 'wet' years, i.e., years for which the percentage deviations of rainfall
and flood index
from their means remained above their averages. Catch and abundance respectively showed good positive linear correlation with the flood index. E. fimbriata behaved differently; some peaks in the
and
curves occurred in the 'wet' and some in the 'dry' years; and there was no correlation between the annual catch of bonga and either the rainfall or the flood index. The hypothesis, that linear relationships exist between the interannual variations in the hydroregime and the yearly fluctuations in the catch and population structure of some coastal and estuarine fishes, holds true for the catfish, C. nigrodigitatus, but not for bonga, E. fimbriata. 相似文献
9.
Chronic nitrate additions dramatically increase the export of carbon and nitrogen from northern hardwood ecosystems 总被引:22,自引:4,他引:18
Kurt S. Pregitzer Donald R. Zak Andrew J. Burton Jennifer A. Ashby Neil W. MacDonald 《Biogeochemistry》2004,68(2):179-197
A long-term field experiment was initiated to simulate chronic atmospheric N deposition, a widespread phenomenon in industrial regions of the world. Eight years of experimental nitrate (
) additions (3 g
-N m–2 per year) to four different northern hardwood forests located along a 500 km geographic gradient dramatically increased leaching losses of
-N, dissolved organic carbon (DOC), and dissolved organic nitrogen (DON). During the last two water years, the average increase in solution
-N and DON leaching from the
-amended plots was 2.2 g N m–2, equivalent to 72% of the annual experimental N addition. Results indicate that atmospheric N deposition may rapidly saturate some northern hardwood ecosystems across an entire biome in the upper Great Lakes Region of the USA. Changes in soil C and N cycling induced by chronic N deposition have the potential in this landscape to significantly alter the flux of DOC and DON from upland to aquatic ecosystems. Michigan Gradient study site characteristics are similar to those of European forests most susceptible to N saturation. 相似文献
10.
T. B. R. J. Smith W. G. Hopkins N. A. S. Taylor 《European journal of applied physiology and occupational physiology》1994,69(1):44-49
The position of the body and use of the respiratory muscles in the act of rowing may limit ventilation and thereby reduce maximal aerobic power relative to that achieved in cycling or running, in spite of the greater muscle mass involved in rowing. This hypothesis was investigated for three groups of male subjects: nine elite senior oarsmen, eight former senior oarsmen and eight highly trained athletes unskilled in rowing. The subjects performed graded exercise to maximal effort on a rowing ergometer, cycle ergometer and treadmill while respiratory minute volume
and oxygen consumption
were monitored continuously. The VE at a given
during intense submaximal exercise (greater than 75% of maximal
) was not significantly lower in rowing compared with that in cycling and treadmill running for any group, which would suggest that submaximal rowing does not restrict ventilation. At maximal effort,
and
for rowing were less than those for the other types of exercise in all the groups, although the differences were not statistically significant in the elite oarsmen. These data are consistent with a ventilatory limitation to maximal performance in rowing that may have been partly overcome by training in the elite oarsmen. Alternatively, a lower maximal VE in rowing might have been an effect rather than a cause of a lower maximal
if maximal
was limited by the lower rate of muscle activation in rowing. 相似文献
11.
B. Grubb G. E. Folk Jr. 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1978,128(2):185-188
Summary The rate of oxygen consumption (
) by skeletal muscle was investigated in isolated perfused hindlimbs of laboratory rats and lemmings (Lemmus). In both species,
increased in proportion to blood flow rate, even at flow rates 4–5 times above resting level. The slope of the line relating
to skeletal muscle blood flow was significantly greater in the lemming than in the rat. This may be related to the inverse relationship between body weight and metabolic rate. These data support the hypothesis that in small animals a dependent relationship exists between blood flow and skeletal muscle
. 相似文献
12.
D. L. Evans R. J. Rose 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1988,157(6):791-799
Summary Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake (
max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100%
max, the oxygen consumption (
) increased to mean values of approximately 130 ml/kg·min, which represents a 40-fold increase above resting
. At the low and moderate work rates,
showed no significant change from 30 s to 300 s of exercise. At the high work rate, the mean
at 30 s was 80% of the value at 300 s. The HR showed no significant change over time at the moderate work rate but differing responses at the low and high work rates. At the low work rate, the mean HR decreased from 188 beats/min at 30 s to 172 beats/min at 300 s exercise, whereas at the high work rate the mean HR increased from 204 beats/min at 30 s to 221 beats/min at 300 s exercise. No changes in acid base status occurred during exercise at the low work rate. At the moderate work rate, a mild metabolic acidosis occurred which was nonprogressive with time, whereas the high work rate resulted in a progressive metabolic acidosis with a base deficit of 16 mmol/l by 300 s exercise. It is concluded that the kinetics of gas exchange during exercise are more rapid in the horse than in man, despite the relatively greater change in
in the horse when going from rest to high intensity exercise.Symbols and abbreviations E
minute ventilation
-
V
T
tidal volume
-
oxygen uptake
-
carbon dioxide output
-
oxygen pulse
-
ventilatory equivalent for oxygen
-
ventilatory equivalent for carbon dioxide
- R
respiratory exchange ratio
- HR
heart rate
- SBC
standard bicarbonate
- STPD
standard temperature and pressure dry
- BTPS
body temperature and pressure saturated
-
arterial oxygen content
-
arteriovenous oxygen content difference
- Rf
respiratory frequency 相似文献
13.
Linkage analysis using multiple DNA polymorphic markers in normal families and in families with fragile X syndrome 总被引:4,自引:1,他引:3
S. N. Thibodeau H. R. Dorkins K. R. Faulk R. Berry A. C. M. Smith R. Hagerman A. King K. E. Davies 《Human genetics》1988,79(3):219-227
Summary Linkage data, using the polymorphic markers 52A (DXS51), F9, 4D-8(DXS98), and St14(DXS52), are presented from 14 fragile X pedigrees and from 7 normal pedigrees derived from the collection of the Centre d'Étude du Polymorphisme Humaine. A multipoint linkage analysis indicates that the most probable order of these four loci in normal families is DXS51-F9-DXS98-DXS52. Recombination frequencies (
) corresponding to maximum LOD scores (
) were obtained by two-point linkage analysis for a nuber of linkage groups, including: DXS51-F9 (
=5.94,
=0.03), F9-DXS98 (
=0.51,
=0.26), F9-DXS52 (
=0.84,
=0.27), and DXS98-DXS52 (
=0.32,
=0.20). A multipoint linkage analysis of these loci, including the fragile X locus, was also performed for the fragile X population and the data support the relative order (DSX51, F9, DXS98)-FRAXA-DXS52. Recombination frequencies and maximum LOD scores, which again were derived from two-point linkage analyses, were obtained for the linkage groups DXS51-F9 (
=9.96,
=0) and F9-DXS52 (
=0.07,
=0.45), as well as for the groups DXS51-FRAXA (
=2.42,
=0.15), F9-FRAXA (
=1.30,
=0.18), DXS98-FRAXA (
=0.05
=0.36), and DXS52-FRAXA (
=2.42
=0.15). The linkage data was further tested for the presence of genetic heterogeneity both within and between the fragile X and normal families for the intervals DXS51-F9, F9-DXS52, F9-FRAXA, and DXS52-FRAXA using a modification of the A test. Except for the interval F9-FRAXA (P<0.10) there was no evidence of genetic heterogeneity for each of the various linkage groups examined. The heterogeneity detected for the interval F9-FRAXA, however, was most likely due to one family (Fx-28) that displayed very tight linkage between these two loci. 相似文献
14.
Veronique Billat Jean C. Renoux Jacques Pinoteau Bernard Petit Jean P. Koralsztein 《European journal of applied physiology and occupational physiology》1994,69(3):271-273
The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits
max
max in 38 elite male long - distance runners
max = 71.4 ± 5.5 ml.kg–1.min–1 and
max = 21.8 ± 1.2 km.h–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in
max. Tlim value was negatively correlated with
max (r = -0.362, p< 0.05) and
max (r = –0.347, p< 0.05) but positively with LT (%v
max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at
max in a homogeneous group of elite male long-distance runners was inversely related to
max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) . 相似文献
15.
Ivona Aksentijevich Luis Gruberg Elon Pras James E. Balow Jr. Michal Kovo Ephraim Gazit Michael Dean Mordechai Pras Daniel L. Kastner 《Human genetics》1993,91(6):527-534
Familial Mediterranean fever (FMF) is an autosomal recessive disorder of unknown pathogenesis, characterized by recurrent, selflimited attacks of fever with synovitis, peritonitis, or pleurisy. Using DNAs from affected Israeli families, we have recently mapped the gene causing FMF (designated MEF) to the short arm of chromosome 16, with two-point lod scores in excess of 20. In this report we consider the possibility of a second FMF susceptibility locus. Before discovering linkage to markers on chromosome 16, we had found suggestive evidence for linkage to chromosome 17q, with the following maximal two-point lod scores: D17S74 (pCMM86),
= 2.47, (
= 0.20); D17S40 (pLEW101),
= 2.15(
= 0.15); D17S35 (CRI-pP3-1),
= 1.78 (
= 0.15); D17S46 (pLEW108),
= 1.69 (
= 0.18), D17S254,
= 2.30 (
= 0.20). Moreover, multipoint linkage analysis using D17S74 and D17S40 as fixed loci gave
= 3.27 approximately 10 centimorgans (cM) telomeric to D17S40. Data with the chromosome 17 markers alone in our families suggested locus heterogeneity. Nevertheless, our families were not separable into complementary subsets showing linkage either to chromosome 16 or to chromosome 17. We also examined the possibility that the positive lod scores for chromosome 17 might reflect a secondary, modifying locus. By several measures of disease severity, families with positive lod scores for chromosome 17 loci had no worse disease than those with negative lod scores for these loci. We conclude that chromosome 17 does not encode a major FMF susceptibility gene for some of the families, nor does it encode a disease-modifying gene. Rather, it would appear that linkage to chromosome 17 is a false positive (type I) error. These results reemphasize the fact that a lod score of 3.0 corresponds to a posterior probability of linkage of 95%, with an attendant 1 in 20 chance of observing a false positive. 相似文献
16.
Lawrence A. Baker Dr. Wesley W. Weathers Fred N. White 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1972,80(3):312-323
Summary The influence of local temperature changes within the posterior portion of the body on dorsal aorta blood flow (
), femoral arterial pressure (P
a
), peripheral resistance (R), skin blood flow (
) and skeletal muscle blood flow (
) was examined in unanesthetized lizards (Iguana iguana andTubinambis nigropunctatus). In response to local heating of the hind legs and tail
and
increased,P
a
was generally unchanged,R decreased and
decreased or was unchanged (Fig. 2). It is suggested that the acquisition of heat may be favored by diverting the increase in
away from the muscle to the warmer skin. In response to cooling
and
decreased,P
a
was generally unchanged, R increased and
increased or was unchanged. Hence, during cooling the retention of heat may be favored by diverting blood away from the skin to the deeper muscle. The muscle-skin shunt is under sympathetic control since following blockade with phenoxybenzamine HCL (Dibenzyline) muscle blood flow changes in response to temperature were qualitatively similar to those of skin (Fig. 4). These changes in peripheral circulatory patterns are independent of changes in heart rate or deep body temperature.Baker and Weathers were predoctoral and postdoctoral trainees, respectively, under USPHS Grant HE-05696. This study was also supported by NSF Grant GB-8523 and Los Angeles County Heart Association Grant 437IG. 相似文献
17.
Takayoshi Yoshida Koji Yamamoto Masao Udo 《European journal of applied physiology and occupational physiology》1993,66(2):155-160
The purpose of the present study was to assess the relationship between the rapidity of increased gas exchange (i.e. oxygen uptake
) and increased cardiac output (
) during the transient phase following the onset of exercise. Five healthy male subjects performed multiple rest-exercise or light exercise (25 W)-exercise transitions on an electrically braked ergometer at exercise intensities of 50, 75, or 100 W for 6 min, respectively. Each transition was performed at least eight times for each load in random order. The
was obtained by a breath-by-breath method, and
was measured by an impedance method during normal breathing, using an ensemble average. On transitions from rest to exercise,
rapidly increased during phase I with time constants of 6.8–7.3 s. The
also showed a similar rapid increment with time constants of 6.0–6.8 s with an apparent increase in stroke volume (SV). In this phase I,
increased to about 29.7%–34.1% of the steady-state value and
increased to about 58.3%–87.0%. Thereafter, some 20 s after the onset of exercise a mono-exponential increase to steady-state occurred both in
and
with time constants of 26.7–32.3 and 23.7–34.4 s, respectively. The insignificant difference between
and
time constants in phase I and the abrupt increase in both
and SV at the onset of exercise from rest provided further evidence for a cardiodynamic contribution to
following the onset of exercise from rest. 相似文献
18.
P. Pic 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1978,123(2):155-162
Summary In seawater (SW)-adaptedMugil andFundulus, gill effluxes of Na+
and of Cl–
and the simultaneously recorded transgill potential (P.D.) differ according to whether they are measured in stressed or rested animals.In rested animals of the two species, transfer to Ringer's solution considerably reduces the P.D. but not
. InFundulus,
is also decreased. Transfer of the two species from SW to fresh water (FW) reduces
and
by 75 to 85% and leads to a large inversion of P.D. When K+ is added to FW, a gill depolarization occurs, as well as a large increase of
and
.These results suggest that: 1) the P.D. originates primarily from the diffusion of cations, the gill permeability to Na+ (
) being greater than that to Cl– (
), 2) a Cl–/Cl– exchange independent of P.D. is associated with the Cl– pump; 3) Cl– pump activity is linked to Na+/K+ exchange which in turn is associated to a Na+/Na+ exchange diffusion mechanism.In stressed individuals of the two species, the P.D. in SW, as well as the P.D. changes observed during transfer experiments, are considerably reduced. The decrease of
and
observed after transfer from SW to FW are also minimised. Changes are smaller inFundulus. The decrease of P.D. characterizing stressed animals may be at least in part due to a 3 to 4 fold increase of
which becomes equal to
in both species.As a result of stress, the K+-activated Na+ and Cl– excretion mechanisms are totally inhibited inFundulus and partially so inMugil.Stress response seems more intense inFundulus and recovery from stress faster inMugil. 相似文献
19.
Gregory K. Snyder Wesley W. Weathers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1977,117(3):291-301
Summary Resting rates of O2 consumption
against
, exercise endurance times and
during recovery from vigorous exercise were measured inSceloporus occidentalis captured near sea level and inS. graciosus captured above 2850 m. Oxygen consumption against
was also measured inS. occidentalis captured above 2850 m. When
was recorded continuously, as ambient
was slowly reduced from 155 Torr, it became directly dependent upon ambient
between 110 and 120 Torr. The critical
for the high altitude lizards was lower than that for the lowland lizards, which enabled the former to maintain relatively higher
's when ambient
was reduced below 120 Torr. The high altitude lizards also had significantly greater endurance when stimulated to exercise at 1600 m (
130 Torr). Both the higher
under hypoxia and the greater endurance roughly parallel a significantly greater maximum
in the high altitude lizards. At a simulated altitude of 3600 m (
100 Torr), maximum
and rate of recovery of the O2 debt calculated from post active
were significantly reduced in the lowland but not the high altitude lizards. The effects of simulated altitude conditions on the lowland but not the mountaine animals indicate adaptations to altitude in these sceloporine lizards. We did not find any consistent relationship between organ/body weight ratios or hematocrit and our measures of
endurance or the altitude at which the lizards were captured. 相似文献
20.
Takayoshi Yoshida Junji Kamiya Kouji Hishimoto 《European journal of applied physiology and occupational physiology》1995,70(6):482-486
To assess the rate-limiting factor of oxygen uptake (
) kinetics at the onset of exercise, six healthy male sedentary subjects performed repeated one-legged constant-load cycle exercise. The one-legged constant-load exercise test consisted of two 5-min periods of pedalling at an exercise intensity of 50 W, with a 5-min rest between periods (these exercise periods, i.e. first and second exercises, were performed by the same leg). The exercise was then repeated using the other leg. In addition, two-legged incremental exercise was investigated to establish whether
kinetics were affected by slower heart rate kinetics. The incremental exercise test consisted of two-legged pedalling first with the cycle unloaded as a warm-up for 5 min followed by 50-W exercise for 5 min. The exercise intensity was then increased to 100 W for 5 min. During exercise, gas exchange parameters were determined by the breath-by-breath method and cardiac output (
) was determined continuously by an impedance technique with a computer-based automated system. To determine the kinetics of heart rate (HR),
and
, a best fit procedure was employed using least-squares criteria with a time delay, except during the initial increase. During the one-legged constant-load exercise test,
kinetics were significantly accelerated by repeated exercise using the same leg. On the other hand, when the exercise was changed to the other leg,
kinetics were significantly slower, although
kinetics continued to be faster. During the incremental exercise test, although the HR response was slower at the transition from 50-W to 100-W exercise than at the transition from warm-up to 50-W exercise, there were no significant changes in
kinetics. These findings suggest that
kinetics may be affected by metabolic conditions in the muscle, but not by blood flow (
and/or HR) kinetics. 相似文献