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1.
Fritz Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(6):590-597
Summary Dieary lipids strongly influence the pattern of torpor and the body lipid composition of mammalian hibernators. The object of the present study was to investigate whether these diet-induced physiological and biochemical changes also occur in species that show shallow, daily torpor. Deer mice, Peromyscus maniculatus, were fed with rodent chow (control diet) or rodent chow with either 10% sunflower seed oil (unsaturated diet) or 10% sheep fat (saturated diet). Animals on the unsaturated diet showed a greater occurrence of torpor (80–100% vs 26–43%), longer torpor bouts (4.5 vs 2.25 h), a lower metabolic rate during torpor (0.96 vs 2.25 ml O2·g-1·h-1), and a smaller loss of body mass during withdrawal of food (2.35 vs 3.90 g) than animals on the saturated diet; controls were intermediate. These diet-induced physiological changes were associated with significant alterations in the fatty acid composition of depot fat, leg muscle and brain total lipids, and heart mitochondrial phospholipids. Significant differences in the total unsaturated fatty acid (UFA) content between animals on saturated and unsaturated diet were observed in depot fat (55.7% vs 81.1%) and leg muscle (56.4% vs 72.1%). Major compositional differences between diet groups also occurred in the concentration of n6 and/or n3 fatty acids of brain and heart mitochondria. The study suggests that dietary lipids may play an important role in the seasonal adjustment of physiology in heterothermic mammals.Abbreviations EDTA
ethylenediaminetetra-acetic acid
- HEPES
N-2 hydroxyethylpiperazine-N1-2-ethanesulphonic acid
- MUFA
monounsaturated fatty acids
- PUFA
polyunsaturated fatty acids
- RMR
Testing metabolic rate
- SD
standard deviation
- SFA
saturated fatty acids
- SNK
Student-Newman-Keuls test
- T1
air temperature
- Tb
body temperature
- UFA
unsaturated fatty acids
-
rate of oxygen consumption
Dedicated to the late John K. Raison 相似文献
2.
Little is known about how animals from tropical and subtropical climates adjust their energy expenditure to cope with seasonal
changes of climate and food availability. To provide such information, we studied the thermal physiology, torpor patterns
and energetics of the nocturnal blossom-bat (Syconycteris australis 18 g) from a subtropical habitat in both summer and winter. In both seasons, S. australis frequently entered daily torpor at ambient temperatures between 12 and 25°C when food and water were withheld. Unlike patterns
observed in temperate animals, mean minimum metabolic rates during torpor were lower in summer (0.47 ± 0.07 ml O2 g−1 h−1) than in winter (0.75 ± 0.11 ml O2 g−1 h−1). Body temperatures during torpor were regulated at 19.3 ± 1.0°C in summer and at 23.4 ± 2.0°C in winter. Torpor bout duration
was significantly longer in summer (7.3 ± 0.6 h) than in winter (5.5 ± 0.3 h), but in both seasons, bout duration was not
affected by ambient temperature. Consequently, average daily metabolic rates were also significantly lower in summer than
in winter. Body temperatures and metabolic rates in normothermic bats did not change with season. Our findings on seasonal
changes of torpor in this bat from the subtropics are opposite to those made for many species from cold climates which generally
show deeper and longer torpor in winter and are often entirely homeothermic in summer. More pronounced torpor in subtropical
S. australis in summer may be due to low or unpredictable nectar availability, short nights which limit the time available for foraging,
and long days without access to food. Thus, the reversed seasonal response of this subtropical bat in comparison to temperate
species may be an appropriate response to ecological constraints.
Received: 6 May 1997 / Accepted: 19 October 1997 相似文献
3.
Geiser F Brigham RM 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(2):153-162
Previous studies have suggested that Australian long-eared bats (Nyctophilus) differ from northern-hemisphere bats with respect to their thermal physiology and patterns of torpor. To determine whether
this is a general trait of Australian bats, we characterised the temporal organisation of torpor and quantified metabolic
rates and body temperatures of normothermic and torpid Australian bats (Nyctophilus geoffroyi, 7 g and N. gouldi, 10 g) over a range of air temperatures and in different seasons. The basal metabolic rate of normothermic bats was 1.36 ± 0.17 ml g−1 h−1 (N. geoffroyi) and 1.22 ± 0.13 ml g−1 h−1 (N. gouldi), about 65% of that predicted by allometric equations, and the corresponding body temperature was about 36 °C. Below an air
temperature of about 25 °C bats usually remained normothermic for only brief periods and typically entered torpor. Arousal
from torpor usually occurred shortly after the beginning of the dark phase and torpor re-entry occurred almost always during
the dark phase after normothermic periods of only 111 ± 48 min (N. geoffroyi) and 115 ± 66 min (N. gouldi). At air temperatures below 10 °C, bats remained torpid for more than 1 day. Bats that were measured overnight had steady-state
torpor metabolic rates representing only 2.7% (N. geoffroyi) and 4.2% (N. gouldi) of the basal metabolic rate, and their body temperatures fell to minima of 1.4 and 2.3 °C, respectively. In contrast, bats
measured entirely during the day, as in previous studies, had torpor metabolic rates that were up to ten times higher than
those measured overnight. The steady-state torpor metabolic rate of thermoconforming torpid bats showed an exponential relationship
with body temperature (r
2 = 0.94), suggesting that temperature effects are important for reduction of metabolic rate below basal levels. However, the
75% reduction of metabolic rate between basal metabolic rate and torpor metabolic rate at a body temperature of 29.3 °C suggests
that metabolic inhibition also plays an important role. Torpor metabolic rate showed little or no seasonal change. Our study
suggests that Australian Nyctophilus bats have a low basal metabolic rate and that their patterns of torpor are similar to those measured in bats from the northern
hemisphere. The low basal metabolic rate and the high proclivity of these bats for using torpor suggest that they are constrained
by limited energy availability and that heterothermy plays a key role in their natural biology.
Accepted: 22 November 1999 相似文献
4.
Schmid J Speakman JR 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(8):633-641
We aimed to investigate the pattern of utilisation of torpor and its impact on energy budgets in free-living grey mouse lemurs
(Microcebus murinus), a small nocturnal primate endemic to Madagascar. We measured daily energy expenditure (DEE) and water turnover using doubly
labelled water, and we used temperature-sensitive radio collars to measure skin temperature (T
sk) and home range. Our results showed that male and female mouse lemurs in the wild enter torpor spontaneously over a wide
range of ambient temperatures (T
a) during the dry season, but not during the rainy season. Mouse lemurs remained torpid between 1.7–8.9 h with a daily mean
of 3.4 h, and their T
sk s fell to a minimum of 18.8 °C. Mean home ranges of mouse lemurs which remained normothermic were similar in the rainy and
dry season. During the dry season, the mean home range of mouse lemurs showing daily torpor was significantly smaller than
that of animals remaining normothermic. The DEE of M. murinus remaining normothermic in the rainy season (122 ± 65.4 kJ day−1) was about the same of that of normothermic mouse lemurs in the dry season (115.5 ± 27.3 kJ day−1). During the dry season, the mean DEE of M. murinus that utilised daily torpor was 103.4 ± 32.7 kJ day−1 which is not significantly different from the mean DEE of animals remaining normothermic. We found that the DEE of mouse
lemurs using daily torpor was significantly correlated with the mean temperature difference between T
sk and T
a (r
2=0.37) and with torpor bout length (r
2
=0.46), while none of these factors explained significant amounts of variation in the DEE of the mouse lemurs remaining normothermic.
The mean water flux rate of mouse lemurs using daily torpor (13.0 ± 4.1 ml day−1) was significantly lower than that of mouse lemurs remaining normothermic (19.4 ± 3.8 ml day−1), suggesting the lemurs conserve water by entering torpor. Thus, this first study on the energy budget of free-ranging M. murinus demonstrates that torpor may not only reflect its impact on the daily energy demands, but involve wider adaptive implications
such as water requirements.
Accepted: 29 August 2000 相似文献
5.
W. Bartels B. S. Law F. Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(3):233-239
Little is known about torpor in the tropics or torpor in megachiropteran species. We investigated thermoregulation, energetics
and patterns of torpor in the northern blossom-bat Macroglossus minimus (16 g) to test whether physiological variables may explain why its range is limited to tropical regions. Normothermic bats
showed a large variation in body temperature (T
b) (33 to 37 °C) over a wide range of ambient temperatures (T
as) and a relatively low basal metabolic rate (1.29 ml O2 g−1 h−1). Bats entered torpor frequently in the laboratory at T
as between 14 and 25 °C. Entry into torpor always occurred when lights were switched on in the morning, independent of T
a. MRs during torpor were reduced to about 20–40% of normothermic bats and T
bs were regulated at a minimum of 23.1 ± 1.4 °C. The duration of torpor bouts increased with decreasing T
a in non-thermoregulating bats, but generally terminated after 8 h in thermoregulating torpid bats. Both the mean minimum T
b and MR of torpid M. minimus were higher than that predicted for a 16-g daily heterotherm and the T
b was also about 5 °C higher than that of the common blossom-bat Syconycteris australis, which has a more subtropical distribution. These observations suggest that variables associated with torpor are affected
by T
a and that the restriction to tropical areas in M. minimus to some extent may be due to their ability to enter only very shallow daily torpor.
Accepted: 22 September 1997 相似文献
6.
Moro D Bradshaw SD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):538-548
A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of
two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day−1 and 1.2 ± 0.4 ml · day−1, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day−1 and 2.0 ± 0.3 ml · day−1, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher
in M. domesticus (1.1 ± 0.1 mg H2O · g−0.122 · h−1) than in L. lakedownensis (0.6 ± 0.1 mg H2O · g−0.122 · h−1). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following
an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations
up to 1 mol · l−1, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate
was significantly higher in M. domesticus (3.3 ± 0.2 mg O2 · g−0.75 · h−1) than in L. lakedownensis (2.5 ± 0.1 mg O2 · g−0.75 · h−1). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose
relatively high sodium fluxes may reflect sodium associated with available food.
Accepted: 16 August 1999 相似文献
7.
Willis CK Turbill C Geiser F 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2005,175(7):479-486
Data on thermal energetics for vespertilionid bats are under-represented in the literature relative to their abundance, as
are data for bats of very small body mass. Therefore, we studied torpor use and thermal energetics in one of the smallest
(4 g) Australian vespertilionids, Vespadelus vulturnus. We used open-flow respirometry to quantify temporal patterns of torpor use, upper and lower critical temperatures (T
uc and T
lc) of the thermoneutral zone (TNZ), basal metabolic rate (BMR), resting metabolic rate (RMR), torpid metabolic rate (TMR),
and wet thermal conductance (C
wet) over a range of ambient temperatures (T
a). We also measured body temperature (T
b) during torpor and normothermia. Bats showed a high proclivity for torpor and typically aroused only for brief periods. The
TNZ ranged from 27.6°C to 33.3°C. Within the TNZ T
b was 33.3±0.4°C and BMR was 1.02±0.29 mlO2 g−1 h−1 (5.60±1.65 mW g−1) at a mean body mass of 4.0±0.69 g, which is 55 % of that predicted for a 4 g bat. Minimum TMR of torpid bats was 0.014±0.006 mlO2 g−1 h−1 (0.079±0.032 mW g−1) at T
a=4.6±0.4°C and T
b=7.5±1.9. T
lc and C
wet of normothermic bats were both lower than that predicted for a 4 g bat, which indicates that V. vulturnus is adapted to minimising heat loss at low T
a. Our findings support the hypothesis that vespertilionid bats have evolved energy-conserving physiological traits, such as
low BMR and proclivity for torpor. 相似文献
8.
Bahr M Stams AJ De la Rosa F García-Encina PA Muñoz R 《Applied microbiology and biotechnology》2011,90(4):1527-1536
The influence of the carbon oxidation–reduction state (CORS) of organic pollutants on their biodegradation in enclosed algal–bacterial
photobioreactors was evaluated using a consortium of enriched wild-type methanotrophic bacteria and microalgae. Methane, methanol
and glucose (with CORS −4, −2 and 0, respectively) were chosen as model organic pollutants. In the absence of external oxygen
supply, microalgal photosynthesis was not capable of supporting a significant methane and methanol biodegradation due to their
high oxygen demands per carbon unit, while glucose was fully oxidized by photosynthetic oxygenation. When bicarbonate was
added, removal efficiencies of 37 ± 4% (20 days), 65 ± 4% (11 days) and 100% (2 days) were recorded for CH4, CH3OH and C6H12O6, respectively due to the additional oxygen generated from photosynthetic bicarbonate assimilation. The use of NO3− instead of NH4+ as nitrogen source (N oxidation–reduction state of +5 vs. −3) resulted in an increase in CH4 degradation from 0 to 33 ± 3% in the absence of bicarbonate and from 37 ± 4% to 100% in the presence of bicarbonate, likely
due to a decrease in the stoichiometric oxygen requirements and the higher photosynthetic oxygen production. Hypothetically,
the CORS of the substrates might affect the CORS of the microalgal biomass composition (higher lipid content). However, the
total lipid content of the algal–bacterial biomass was 19 ± 7% in the absence and 16 ± 2% in the presence of bicarbonate. 相似文献
9.
C. Lydersen K. M. Kovacs M. O. Hammill 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):81-88
In this study we measured growth and milk intake and calculated energy intake and its allocation into metabolism and stored
tissue for hooded seal (Cystophora cristata) pups. In addition, we measured mass loss, change in body composition and metabolic rate during the first days of the postweaning
fast. The mean body mass of the hooded seal pups (n = 5) at the start of the experiments, when they were new-born, was 24.3 ± 1.3 kg (SD). They gained an average of 5.9 ± 1.1.
kg · day−1 of which 19% was water, 76% fat and 5% protein. This corresponds to an average daily energy deposition of 179.8 ± 16.0 MJ.
The pups were weaned at an average body mass of 42.5 ± 1.0 kg 3.1 days after the experiment was initiated. During the first
days of the postweaning fast the pups lost an average of 1.3 ± 0.5␣kg of body mass daily, of which 56% was water, 16% fat
and 28% protein. During the nursing period the average daily water influx for the pups was 124.6 ± 25.8 ml · kg−1. The average CO2 production during this period was 1.10 ± 0.20 ml · g−1 · h−1, which corresponds to a field metabolic rate of 714 ± 130 kJ · kg−1 · day−1, or 5.8 ± 1.1 times the predicted basal metabolic rate according to Kleiber (1975). During the postweaning fast the average
daily water influx was reduced to 16.1 ± 6.6 ml · kg−1. The average CO2 production in␣this period was 0.58 ± 0.17 ml · g−1 · h−1 which corresponds to a field metabolic rate of 375 ± 108 kJ · kg−1 · day−1 or 3.2 ± 0.9 times the predicted basal metabolic rate. Average values for milk composition were 33.5% water, 58.6% fat and
6.2% protein. The pups drank an average of 10.4 ± 1.8␣kg of milk daily, which represents an energy intake of 248.9 ± 39.1
MJ · day−1. The pups were able to store 73.2 ± 7.7% of this energy as body tissue.
Accepted: 15 August 1996 相似文献
10.
Theodore J. Angelopoulos Rebecca Lewis Thanassis Jamurtas Chris Schumann 《European journal of applied physiology and occupational physiology》1998,77(6):556-559
We characterized the effect of ten days of training on lipid metabolism in 6 [age 37.2 (2.3) years] sedentary, obese [BMI
34.4 (3.0) kg · m−2] males with normal glucose tolerance. An oral glucose tolerance test was performed prior to and at the end of the 10 d of
training period. The duration of each daily exercise session was 40 min at an intensity equivalent to ˜75% of the age predicted
maximum heart rate. Blood measurements were performed after an overnight fast, before and at the end of the 10 d period. Plasma
triacylglycerol was significantly (p < 0.05) reduced following exercise training (2.15 ± 0.29 vs. 1.55 ± 0.28 mmol · l−1). Very low density lipoprotein-triacylglycerol was also significantly (p < 0.05) reduced (1.82 ± 0.3 vs. 1.29 ± 0.29 mmol · l−1). No significant changes in high density lipoprotein-cholesterol were observed as a result of training. Following training
fasting plasma glucose and fasting plasma insulin were significantly reduced [Glucose: 5.9 (0.2) mmol · l−1 vs. 5.3 (0.22) mmol · l−1 (p < 0.05); Insulin 264.3 (53.8) ρ · mol · l−1 vs. 200.9 (30.1) ρ · mol · l−1, p = 0.05]. The total area under the glucose curve during the OGTT decreased significantly (p < 0.05). These preliminary data suggest that short-term exercise, without concomitant loss of body mass, induces favorable
changes in plasma triacylglycerol, and very low density lipoprotein-triacylglycerol and glucose tolerance but has no effect
on high density lipoproteincholesterol.
Accepted: 7 January 1998 相似文献
11.
J. Langfort R. Zarzeczny W. Pilis K. Nazar H. Kaciuba-Ucitko 《European journal of applied physiology and occupational physiology》1997,76(2):128-133
The aim of this study was to find out whether a low-carbohydrate diet (L-CHO) affects: (1) the capacity for all-out anaerobic
exercise, and (2) hormonal and metabolic responses to this type of exercise. To this purpose, eight healthy subjects underwent
a 30-s bicycle Wingate test preceded by either 3 days of a controlled mixed diet (130 kJ/kg of body mass daily, 50% carbohydrate,
30% fat, 20% protein) or 3 days of an isoenergetic L-CHO diet (up to 5% carbohydrate, 50% fat, 45% protein) in a randomized
order. Before and during 1 h after the exercise venous blood samples were taken for measurement of blood lactate (LA), β-hydroxybutyrate
(β-HB), glucose, adrenaline (A), noradrenaline (NA) and insulin levels. Oxygen consumption (V˙O2) was also determined. It was found that the L-CHO diet diminished the mean power output during the 30-s exercise bout [533
(7) W vs 581 (7) W, P < 0.05] without changing the maximal power attained during the first or second 5-s interval of the exercise. In comparison
with the data obtained after the consumption of a mixed diet, after the consumption of a L-CHO diet resting plasma concentrations
of β-HB [2.38 (0.18) vs 0.23 (0.01) mmol · l−1, P < 0.001] and NA [4.81 (0.68) vs 2.2 (0.31) nmol · l−1, P < 0.05] were higher, while glucose [4.6 (0.1) vs 5.7 (0.2) mmol · l−1, P < 0.05] and insulin concentrations [11.9 (0.9) vs 21.8 (1.8) mU · l−1] were lower. The 1-h post-exercise excess of V˙O2 [9.1 (0.25) vs 10.6 (0.25) l, P < 0.05], and blood LA measured 3 min after the exercise [9.5 (0.4) vs 10.6 (0.5) mmol · l−1, P < 0.05] were lower following the L-CHO treatment, whilst plasma NA and A concentrations reached higher values [2.24 (0.40) vs
1.21 (0.13) nmol · l−1 and 14.30 (1.41) vs 8.20 (1.31) nmol · l−1, P < 0.01, respectively]. In subjects on the L-CHO diet, the plasma β-HB concentration decreased quickly after exercise, attaining
≈30% of the pre-exercise value within 60 min, while insulin and glucose levels were elevated. The main conclusions of this
study are: (1) a L-CHO diet is detrimental to anaerobic work capacity, possibly because of a reduced muscle glycogen store
and decreased rate of glycolysis; (2) reduced carbohydrate intake for 3 days enhances activity of the sympathoadrenal system
at rest and after exercise.
Accepted: 31 January 1997 相似文献
12.
Ercan Varol Selahattin Akcay I. Hakki Ersoy Mehmet Ozaydin Banu Kale Koroglu Simge Varol 《Biological trace element research》2010,133(2):121-127
Sixty-three patients with endemic fluorosis (36 males/27 females; mean age 33.9 ± 8.6 years) and 45 age-, sex-, and body mass
index-matched healthy controls (30 males/15 females; mean age 32.7 ± 8.8 years) were included in this study. Aortic stiffness
indices, aortic strain (AS), aortic distensibility (AD), and aortic strain index (ASI) were calculated from the aortic diameters
measured by echocardiography and blood pressure obtained by sphygmomanometry. The urine fluoride levels of fluorosis patients
were significantly higher than control subjects as expected (1.9 ± 0.1 mg/l vs. 0.4 ± 0.1 mg/l, respectively; P < 0.001). AS and AD were significantly lower in fluorosis patients than in the controls (for AS 5.3 ± 3.6 vs. 8.0 ± 3.4%;
P < 0.001 and for AD 0.2 ± 0.1 vs. 0.3 ± 0.1 cm2 dyn−1 10−3; P < 0.001, respectively). In contrast, signicantly higher ASI was observed in fluorosis patients than in the controls (3.4 ± 0.6
vs. 3.0 ± 0.4; P < 0.001, respectively). The results of our study demonstrate that elastic properties of ascending aorta are impaired in patients
with endemic fluorosis. 相似文献
13.
Long-term exposure of native vegetation to elevated atmospheric CO2 concentrations is expected to increase C inputs to the soil and, in ecosystems with seasonally dry periods, to increase soil
moisture. We tested the hypothesis that these indirect effects of elevated CO2 (600 μl l−1 vs 350 μl l−1) would improve conditions for microbial activity and stimulate emissions of nitrous oxide (N2O), a very potent and long-lived greenhouse gas. After two growing seasons, the mean N2O efflux from monoliths of calcareous grassland maintained at elevated CO2 was twice as high as that measured from monoliths maintained at current ambient CO2 (70 ± 9 vs 37 ± 4 μg N2O m−2 h−1 in October, 27 ± 5 vs 13 ± 3 μg N2O m−2 h−1 in November after aboveground harvest). The higher N2O emission rates at elevated CO2 were associated with increases in soil moisture, soil heterotrophic respiration, and plant biomass production, but appear
to be mainly attributable to higher soil moisture. Our results suggest that rising atmospheric CO2 may contribute more to the total greenhouse effect than is currently estimated because of its plant-mediated effects on soil
processes which may ultimately lead to increased N2O emissions from native grasslands.
Received: 11 September 1997 / Accepted: 20 March 1998 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.
Schröder B Vössing S Breves G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(7):487-494
From various in vivo and in vitro studies it has been shown that the rumen represents a significant site of Ca2+ absorption in sheep and goats. It was the aim of the present study to further characterize the underlying mechanisms. Unidirectional
flux rates of Ca2+ across rumen wall epithelia of sheep were measured in vitro by applying the Ussing-chamber technique in the absence of electrochemical
gradients. Under these conditions, significant Ca2+ net flux rates (Jnet) clearly indicate the presence of active mechanisms for Ca2+ transport. Short chain fatty acids (SCFAs) caused highest stimulation of Ca2+ Jnet (6.3 ± 1.9 nmol · cm−2 · h−1) when used as a mixture of acetate, proprionate and butyrate in physiological proportions (36, 15, 9 mmol · l−1, respectively). The effect of 30 mmol · l−1 butyrate (3.2 ± 0.6 nmol · cm−2 · h−1) was higher than respective amounts of propionate and acetate (0.6 ± 0.8 nmol · cm−2 · h−1 and 0.9 ± 0.8 nmol · cm−2 · h−1, respectively). Eliminating SCFAs resulted in Ca2+ Jnet of 0.4 ± 1.1 nmol . cm−2 . h−1. Addition of Ca channel blocker verapamil (mucosal 1 mmol · l−1) had no significant effect on SCFA-stimulated Jnet of Ca2+, whereas application of Na+/H+ inhibitor amiloride (mucosal 1 mmol · l−1) further enhanced the Ca2+ Jnet by >65%. The Ca2+-pump inhibitor vanadate had no significant effect on Jnet of Ca2+. Dietary Ca depletion enhanced calcitriol plasma concentrations but had no effect on active Ca2+ absorption across the rumen wall of sheep. In addition, no effect on active Ca2+ absorption could be observed during early lactation. In conclusion, there is clear evidence for the rumen as a main site
for active Ca2+ absorption in sheep. Our results suggest the presence of a Ca2+/H+ exchange mechanism in the apical membrane of rumen epithelial cells which depends on SCFA absorption and which does not seem
to be under the control of calcitriol. Basolateral Ca2+ extrusion occurs independently from Ca2+-pump activity and may be accomplished via Na+/Ca2+ exchange.
Accepted: 29 June 1999 相似文献
16.
R. Oelkrug G. Heldmaier C. W. Meyer 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(1):137-145
In eutherian mammals, uncoupling protein 1 (UCP1) mediated non-shivering thermogenesis from brown adipose tissue (BAT) provides
a mechanism through which arousal from torpor and hibernation is facilitated. In order to directly assess the magnitude by
which the presence or absence of UCP1 affects torpor patterns, rewarming and arousal rates within one species we compared
fasting induced torpor in wildtype (UCP1+/+) and UCP1-ablated mice (UCP−/−). Torpor was induced by depriving mice of food for up to 48 h and by a reduction of ambient temperature (T
a) from 30 to 18°C at four different time points after 18, 24, 30 and 36 h of food deprivation. In most cases, torpor bouts
occurred within 20 min after the switch in ambient temperature (30–18°C). Torpor bouts expressed during the light phase lasted
3–6 h while significantly longer bouts (up to 16 h) were observed when mice entered torpor during the dark phase. The degree
of hypometabolism (5–22 ml h−1) and hypothermia (19.5–26.7°C) was comparable in wildtype and UCP1-ablated mice, and both genotypes were able to regain normothermia.
In contrast to wildtype mice, UCP1-ablated mice did not display multiple torpor bouts per day and their peak rewarming rates
from torpor were reduced by 50% (UCP1+/+: 0.24 ± 0.08°C min−1; UCP1−/−: 0.12 ± 0.04°C min−1). UCP1-ablated mice therefore took significantly longer to rewarm from 25 to 32°C (39 vs. 70 min) and required 60% more energy
for this process. Our results demonstrate the energetic benefit of functional BAT for rapid arousal from torpor. They also
suggest that torpor entry and maintenance may be dependent on endogenous rhythms. 相似文献
17.
Herbert R. L. Drouin 《European biophysics journal : EBJ》1999,28(7):600-604
A new ion-selective liquid membrane microelectrode, based on the neutral carrier 1,1′-bis(2,3-naphtho-18-crown-6), is described
that shows the dependence of EMF on the activity of divalent putrescine cations a
Put, with the linear slope s
Put = 26 ± 3 mV/decade (mean ± SD, N = 18), in the range 10−4–10−1 M at 25 ± 1 °C. Values of potentiometric putrescine cation selectivity coefficients of logK
Pot
Put
j
(mean ± SD, N) are obtained by the separate solution method for the ions K+ (1.0 ± 0.4, 10), Na+ (−1.2 ± 0.4, 8), Ca2+ (−2.3 ± 0.5, 10) and Mg2+ (−2.5 ± 0.5, 7). The microelectrode can be applied for the direct analysis of the activities of free divalent putrescine
cations in the range 5 × 10−4 to 10−1 M in an extracellular ionic environment. Established analytical methods, e.g. high performance liquid chromatography, determine
the total concentration of the derivatives of free and bound putrescine.
Received: 20 December 1998 / Revised version: 7 May 1999 / Accepted: 27 May 1999 相似文献
18.
To identify the importance of arbuscular mycorrhizal fungi (AMF) colonizing wetland seedlings following flooding, we assessed
the effects of AMF on seedling establishment of two pioneer species, Bidens frondosa and Eclipta prostrata grown under three levels of water availability and ask: (1) Do inoculated seedlings differ in growth and development from
non-inoculated plants? (2) Are the effects of inoculation and degree of colonization dependent on water availability? (3)
Do plant responses to inoculation differ between two closely related species? Inoculation had no detectable effects on shoot
height, or plant biomass but did affect biomass partitioning and root morphology in a species-specific manner. Shoot/root
ratios were significantly lower in non-inoculated E. prostrata plants compared with inoculated plants (0.381 ± 0.066 vs. 0.683 ± 0.132). Root length and surface area were greater in non-inoculated
E. prostrata (259.55 ± 33.78 cm vs. 194.64 ± 27.45 cm and 54.91 ± 7.628 cm2 vs. 46.26 ± 6.8 cm2, respectively). Inoculation had no detectable effect on B. frondosa root length, volume, or surface area. AMF associations formed at all levels of water availability. Hyphal, arbuscular, and
vesicular colonization levels were greater in dry compared with intermediate and flooded treatments. Measures of mycorrhizal
responsiveness were significantly depressed in E. prostrata compared with B. frondosa for total fresh weight (−0.3 ± 0.18 g vs. 0.06 ± 0.06 g), root length (−0.78 ± 0.28 cm vs.−0.11 ± 0.07 cm), root volume (−0.49 ± 0.22 cm3 vs. 0.06 ± 0.07 cm3), and surface area (−0.59 ± 0.23 cm2 vs.−0.03 ± 0.08 cm2). Given the disparity in species response to AMF inoculation, events that alter AMF prevalence in wetlands could significantly
alter plant community structure by directly affecting seedling growth and development. 相似文献
19.
D. A. Gray S. K. Maloney 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(8):558-562
The relationship between body temperature (T
b) and the plasma concentrations of arginine vasotocin (AVT) and angiotensin II (AII) was examined in conscious, adult Pekin
ducks. Exposure of birds to an ambient temperature of 40 °C for 3 h increased T
b by about 1.5 °C and increased breathing rate five-fold. Plasma osmolality was elevated from the normothermic value of 294.9 ± 1.4
mosmol kg−1 by about 8 mosmol kg−1 Circulating AVT levels increased by about 2 pg ml−1 from a basal concentration of 4.98 ± 0.15 pg ml−1, a rise which could be accounted for by the change in osmotic status. Plasma AII concentrations were unchanged from the pre-heat
exposure value of 31.8 ± 3.4 pg ml−1. Time control birds, exposed only to an ambient temperature of 22 °C demonstrated no significant changes in any of the measured
variables. The results suggest that an increased T
b has no direct effect on the circulating concentrations of AVT or AII in ducks.
Accepted: 2 June 1997 相似文献
20.
C. E. Crocker J. J. Cech Jr. 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(1):50-60
The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO2, PO2, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia
(water PCO2 < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25–35 Torr) and a final return to normocapnia at 19 ± 0.5 °C. Acute
(≤ 2h) hypercapnia significantly increased arterial PCO2 (8-fold increase), ventilation frequency (2-fold increase), plasma HCO3
− (2.3-fold) and decreased arterial pH (to 7.15 ± 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly
increased, and arterial pH reached its nadir (7.10 ± 0.03). During the 72- and 96-h-periods, arterial PCO2 (24 ± 4.4 Torr) and ventilatory frequency (105 ± 5 breaths min−1) stabilized, HCO3
− reached its apparent maximum (23.6 ± 0.0 mmol−1), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored
arterial PCO2 (2.5 ± 0.14 Torr), HCO3
− (7.4 ± 0.59 mmol · l−1), ventilation frequency (71 ± 7 breaths · min−1), and pH (7.75 ± 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine
“spike”, and increased plasma catecholamines, cortisol, and arterial PO2. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted
in a significantly decreased blood-O2 affinity (Bohr effect), as determined by construction of in vitro blood O2 equilibrium curves at 15 °C and 20 °C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively
affect growth of white sturgeon.
Accepted: 17 August 1997 相似文献