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1.
Determinants of bovine thermal response to heat and solar radiation exposures in a field environment 总被引:4,自引:0,他引:4
Brad Scharf Michael J. Leonard Robert L. Weaber Terry L. Mader G. Leroy Hahn Donald E. Spiers 《International journal of biometeorology》2011,55(4):469-480
Continuous exposure of cattle to summer heat in the absence of shade results in significant hyperthermia and impairs growth
and general health. Reliable predictors of heat strain are needed to identify this condition. A 12-day study was conducted
during a moderate summer heat period using 12 Angus x Simmental (Bos taurus) steers (533 ± 12 kg average body weight) to identify animal and ambient determinations of core body temperature (T
core) and respiration rate (RR) responses to heat stress. Steers were provided standard diet and water ad libitum, and implanted
intraperitoneally with telemetric transmitters to monitor T
core hourly. Visual count of flank movement at 0800 and 1500 hours was used for RR. Dataloggers recorded air temperature (T
a), and black globe temperatures (T
bg) hourly to assess radiant heat load. Analysis was across four periods and 2 consecutive days averaged within each period.
Average T
a and T
bg increased progressively from 21.7 to 30.3°C and 25.3 to 34.0°C, respectively, from the first to fourth periods. A model utilizing
a quadratic function of T
a explained the most variation in T
core (R
2 = 0.56). A delay in response from 1 to 3 h did not significantly improve R
2 for this relationship. Measurements at 0800 and 1500 hours alone are sufficient to predict heat strain. Daily minimum core
body temperature and initial 2-h rise in T
a were predictors of maximum core temperature and RR. Further studies using continuous monitoring are needed to expand prediction
of heat stress impact under different conditions. 相似文献
2.
James D. Cotter Mark J. Patterson Nigel A. S. Taylor 《European journal of applied physiology and occupational physiology》1997,76(2):181-186
We investigated the impact of short-term, moderate humidity heat acclimation upon sweat distribution. Eight males completed
six daily heat exposures [cycling: ambient temperature 39.5 (0.2)°C, relative humidity 59.2 (0.8)%], during which auditory
canal temperature (T
ac) was maintained 1.4°C above pre-exposure levels for 70 min by manipulating the work rate. On days 1 and 6, T
ac and local sweat rates (m˙
sw: eight sites) were monitored. The pre-exposure, resting T
ac and the T
ac sweat threshold decreased from day 1 to day 6 [36.83 (0.05)°C vs 36.62 (0.05)°C, and 36.90 (0.05)°C vs 36.75 (0.05)°C, respectively;
both P<0.05]. However, the sweat-onset time, sweat sensitivity (Δm˙
sw/ΔT
ac) and established m˙
sw were unaltered (P > 0.05). There was also no evidence of a post-acclimation redistribution in established m˙
sw between the eight skin regions, though both the sweat sensitivity and established m˙
sw for the forehead and hand were significantly greater than at the remaining sites (P<0.05). It is concluded that the 5-day heat acclimation regimen provided only a minimal stimulus for sudomotor adaptation.
Accepted: 3 March 1997 相似文献
3.
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
4.
R. Arieli D. Kerem A. Gonen I. Goldenberg O. Shoshani Y. I. Daskalovic A. Shupak 《European journal of applied physiology and occupational physiology》1997,76(1):69-74
A wet suit may not provide adequate thermal protection when diving in moderately cold water (17–18°C), and any resultant
mild hypothermia may impair performance during prolonged diving. We studied heat exchange during a dive to a depth of 5 m
in sea water (17–18.5°C) in divers wearing a full wet suit and using closed-circuit oxygen breathing apparatus. Eight fin
swimmers dived for 3.1 h and six underwater scooter (UWS) divers propelled themselves through the water for 3.7 h. The measurements
taken throughout the dive were the oxygen pressure in the cylinder and skin and rectal temperatures (T
re). Each subject also completed a cold score questionnaire. The T
re decreased continuously in all subjects. Oxygen consumption in the fin divers (1.40 l · min−1) was higher than that of the UWS divers (1.05 l · min−1). The mean total insulation was 0.087°C · m2 · W−1 in both groups. Mean body insulation was 37% of the total insulation (suit insulation was 63%). The reduction in T
re over the 1st hour was related to subcutaneous fat thickness. There was a correlation between cold score and T
re at the end of 1 h, but not after that. A full wet suit does not appear to provide adequate thermal protection when diving
in moderately cold water.
Accepted: 21 January 1997 相似文献
5.
Comparison of hibernation, estivation and daily torpor in the edible dormouse, Glis glis 总被引:2,自引:0,他引:2
Wilz M Heldmaier G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(7):511-521
Three major forms of dormancy in mammals have been classified: hibernation in endotherms is characterised by reduced metabolic
rate (MR) and body temperature (T
b) near ambient temperature (T
a) over prolonged times in the winter. Estivation is a similar form of dormancy in a dry and hot environment during summertime.
Daily torpor is defined as reduced MR and T
b lower than 32 °C, limited to a duration of less than 24 h. The edible dormouse (Glis glis) is capable for all three distinct forms of dormancy. During periods of food restriction and/or low T
a, daily torpor is displayed throughout the year, alternating with hibernation and estivation in winter and summer respectively.
We recorded T
b, O2-consumption and CO2-production in unrestrained dormice at different T
a's for periods of up to several months. Cooling rate and rate of metabolic depression during entrance into the torpid state
was identical in all three forms of dormancy. The same was true for thermal conductance, maximum heat production, duration
of arousal and cost of an arousal. The only difference between hibernation and daily torpor was found in the bout duration.
A daily torpor bout lasted 3–21 h, a hibernation bout 39–768 h. As a consequence of prolonged duration, MR, T
b and also the T
b − T
a gradient decreased to lower values during hibernation bouts when compared to daily torpor bouts. Our findings suggest that
all three forms of dormancy are based on the same physiological mechanism of thermal and metabolic regulation.
Accepted: 27 June 2000 相似文献
6.
Thomas Ruf Beatrice Grafl 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(7):1089-1098
Djungarian hamsters (Phodopus sungorus) tolerate short-term exposure to ambient temperatures (T
as) down to −70°C, but surprisingly, previously appeared to reach maximum sustainable metabolic rate (SusMR) when kept at T
as as high as ≥−2°C. We hypothesized that SusMR in Djungarian hamsters may be affected by the degree of prior cold acclimation
and temporal patterns of T
a changes experienced by the animals, as average T
a declines. After cold-acclimation at +5°C for 6 weeks, hamsters reached rates of SusMR that were 35% higher than previously
determined and were able to maintain positive energy balances down to T
a −9°C. SusMR was unaffected, however, by whether mean cold load was constant or caused by T
as cycling between +3°C and as low as −25°C, at hourly intervals. At mean T
as between +3 and −3°C hamsters significantly reduced body mass and energy expenditure, but were able to maintain stable body
mass at lower T
as (−5 to −9°C). These results indicate that prior cold-acclimation profoundly affects SusMR in hamsters and that body mass
regulation may play an integral part in maintaining positive energy balance during cold exposure. Because the degree of instantaneous
cold load had no effect on SusMR, we hypothesize that limits to energy turnover in Djungarian hamsters are not determined
by the capacity to withstand extreme temperatures (i.e., peripheral limits) but are due to central limitation of energy intake. 相似文献
7.
N. J. Adams B. Pinshow L. Z. Gannes H. Biebach 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(3):195-199
We examined the relationship between body temperature (Tb) of free flying pigeons and ambient water vapor pressure and temperature. Core or near core Tb of pigeons were measured using thermistors inserted into the cloaca and connected to small transmitters mounted on the tail
feathers of free flying tippler pigeons (Columba livia). Wet and dry bulb temperatures were measured using modified transmitters mounted onto free-flying pigeons. These allowed
calculation of relative humidity and hence water vapor pressure at flight altitudes. Mean Tb during flight was 42.0 ± 1.3 °C (n = 16). Paired comparisons of a subset of this data indicated that average in-flight Tb increased significantly by 1.2 ± 0.7 °C (n = 7) over that of birds at rest (t = −4.22, P < 0.05, n = 7) within the first 15 min of takeoff. In addition, there was a small but significant increase in Tb with increasing ambient air (Ta) when individuals on replicate flights (n = 35) were considered. Inclusion of water vapor pressure into the regression model did not improve the correlation between
body temperature and ambient conditions. Flight Tb also increased a small (0.5 °C) but significant amount (t = 2.827, P < 0.05, n = 8) from the beginning to the end of a flight. The small response of Tb to changing flight conditions presumably reflects the efficiency of convection as a heat loss mechanism during sustained
regular flight. The increase in Tb on landing that occurred in some birds was a probable consequence of a sudden reduction in convective heat loss.
Accepted: 2 February 1999 相似文献
8.
Stephen S. Cheung Tom M. McLellan 《European journal of applied physiology and occupational physiology》1998,78(1):50-58
The purpose of the present study was to determine the separate and combined effects of a short-term aerobic training program
and hypohydration on tolerance during light exercise while wearing nuclear, biological, and chemical protective clothing in
the heat (40°C, 30% relative humidity). Males of moderate fitness [<50 ml · kg−1 · min−1 maximal O2 consumption (V˙O2
max
)] were tested while euhydrated or hypohydrated by ≈2% of body weight through exercise and fluid restriction the day preceding
the trials. Tests were conducted before and after either a 2-week program of daily aerobic training (1 h treadmill exercise
at 65% V˙O2
max
for 12 days; n = 8) or a control period (n = 7), which had no effect on any measured variable. The training increased V˙O2
max
by 6.5%, while heart rate (f
c) and the rectal temperature (T
re) rise decreased during exercise in a thermoneutral environment. In the heat, training resulted in a decreased skin temperature
and increased sweat rate, but did not affect f
c, T
re or tolerance time (TT). In both training and control groups, hypohydration significantly increased T
re and f
c and decreased the TT. It was concluded that the short-term aerobic training program had no benefit on exercise-heat tolerance
in this uncompensable heat stress environment.
Accepted: 12 November 1997 相似文献
9.
Silvana Mattiello Elena Formis Sara Barbieri 《International journal of biometeorology》2011,55(2):213-218
The present study monitored daily and seasonal variations of rectal temperature in response to different environmental temperatures
in alpacas bred in the Italian Apennines at 300 m a.s.l. In each season, the rectal temperature of 33 clinically healthy alpacas
was measured three times/day (morning, midday, afternoon). Ambient temperatures were also recorded. Rectal temperatures ranged
from a minimum value of 35.1 to a maximum of 39.4°C, with a maximum daily thermal excursion (ΔTrec) of 3.2°C. Temperatures increased throughout the day, with highly significant differences recorded in both young and adult
animals between all the time bands (P < 0.001). These differences were particularly dramatic for adults in summer, when the mean rectal temperature in the morning
was 36.3 ± 0.13°C, probably as a consequence of recent shearing. Significant ΔTrec differences were recorded depending on the season in both young and adult animals (P < 0.001), with the highest ΔTrec values recorded in summer (although the highest daily ambient excursion value was recorded in winter). In conclusion, similarly
to alpacas bred in their natural environment, alpacas bred in Italy show a wide thermal neutrality zone, which is probably
an adaptive response, that allows the animals to save energy. In the Italian Apennines, in order to prevent situations of
hypothermia, with possible detrimental effects on alpacas’ health and welfare, shearing should be carried out only in warm
seasons. 相似文献
10.
Four species of brown seaweeds, namely Sargassum baccularia, Sargassum binderi, Sargassum siliquosum and Turbinaria conoides, harvested from Port Dickson, Negeri Sembilan, Malaysia were analysed for ash content, alginate yield and alginate properties.
Seaweeds calcined at 450°C were found to have low amount of non-combustible residue as these were not contaminated by calcareous
animals. Alginate was extracted from these seaweeds by two methods: hot and cold. In the hot method, the storing time was
3 h and the processing temperature was 50°C, whilst in the cold method, the sample was stored overnight at room temperature.
Higher yield of alginate was obtained by the hot method compared to the cold method, but alginate extracted by the cold method
gave higher molecular weight. In the hot method, 49.9% of alginate was extracted from S. siliquosum, followed by T. conoides (41.4%), S. binderi (38.9%) and S. baccularia (26.7%). Alginate extracted from T. conoides has an average molecular weight, M
w, of 8.06 × 105 g mol−1, whereas alginate from S. siliquosum was the lowest in M
w (4.81 × 105 g mol−1) when the extraction was done at room temperature. Alginate extracted from S. baccularia was found to be very heat-sensitive. Its M
w has dropped more than 83%, from 7.52 × 105 to 1.23 × 105 g mol−1, when the extraction temperature was raised. The effect of heat on the extent of depolymerisation of the alginate molecule
of the other three brown seaweed species was less significant, with decrease in molecular weight ranging between 13% and 16%. 相似文献
11.
A. S. Weller C. E. Millard P. L. Greenhaff I. A. Macdonald 《European journal of applied physiology and occupational physiology》1998,77(3):217-223
In a previous study, rectal temperature (T
re) was found to be lower, and oxygen consumption (V˙O2) and the respiratory exchange ratio (R) were higher in a cold (+5°C), wet and windy environment (COLD), compared with a thermoneutral environment during intermittent
walking at ≈30% of peak V˙O2 (Weller AS, Millard CE, Stroud MA et al. Am J Physiol 272:R226–R233, 1997). The aim of the present study was to establish
whether these cold-induced responses are influenced by prior fasting, as impaired thermoregulation has been demonstrated in
cold-exposed, resting men following a 48-h fast. To address this question, eight men attempted a 360-min intermittent (15 min
rest, 45 min exercise) walking protocol under COLD conditions on two occasions. In one condition, the subjects started the
exercise protocol ≈120 min after a standard meal (FED/COLD), whereas in the other the subjects had fasted for 36 h (FASTED/COLD).
The first two exercise periods were conducted at a higher intensity (HIGHER, 6 km · h−1 and 10% incline), than the four subsequent exercise periods (LOW, 5 km · h−1 and 0% incline). There was no difference in the time endured in FED/COLD and FASTED/COLD. In FASTED/COLD com pared with FED/COLD,
R was lower during HIGHER and LOW, and T
re was lower during LOW, whereas there was no difference in V˙O2, mean skin temperature and heart rate. Therefore, although the 36-h fast impaired temperature regulation during intermittent
low-intensity exercise in the cold, wet and windy environment, it was unlikely to have been the principal factor limiting
exercise performance under these experimental conditions.
Accepted: 26 August 1997 相似文献
12.
This study compares the thermal ecology of male bearded dragon lizards (Pogona barbata) from south-east Queensland across two seasons: summer (1994–1995) and autumn (1995). Seasonal patterns of body temperature
(T
b) were explored in terms of changes in the physical properties of the thermal environment and thermoregulatory effort. To
quantify thermoregulatory effort, we compared behavioral and physiological variables recorded for observed lizards with those
estimated for a thermoconforming lizard. The study lizards' field T
bs varied seasonally (summer: grand daily mean (GDM) 34.6 ± 0.6°C, autumn: GDM 27.5 ± 0.3°C) as did maximum and minimum available
operative temperatures (summer: GDM T
max 42.1 ± 1.7°C, T
min 32.2 ± 1.0°C, autumn: GDM T
max 31.7 ± 1.2°C, T
min 26.4 ± 0.5°C). Interestingly, the range of temperatures that lizards selected in a gradient (selected range) did not change
seasonally. However, P. barbata thermoregulated more extensively and more accurately in summer than in autumn; lizards generally displayed behaviors affecting
heat load nonrandomly in summer and randomly in autumn, leading to the GDM of the mean deviations of lizards' field T
bs from their selected ranges being only 2.1 ± 0.5°C in summer, compared to 4.4 ± 0.5°C in autumn. This seasonal difference
was not a consequence of different heat availability in the two seasons, because the seasonally available ranges of operative
temperatures rarely precluded lizards from attaining field T
bs within their selected range, should that have been the goal. Rather, thermal microhabitat distribution and social behavior
appear to have had an important influence on seasonal levels of thermoregulatory effort.
Received: 28 April 1997 / Accepted: 29 December 1997 相似文献
13.
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
14.
C. J. Baxter N. Magan B. Lane H. G. Wildman 《Applied microbiology and biotechnology》1998,49(3):328-332
A Phoma sp., known to produce the pharmaceutically active metabolites squalestatin 1 (S1) and squalestatin 2 (S2), was cultured on
malt-extract/agar (MEA) over a range of water activities (a
w, 0.995–0.90) and temperatures (10–35 °C) to investigate the influence on growth and metabolite production. Use of the ionic
solute NaCl to adjust a
w resulted in significantly lower (P < 0.01) squalestatin yields than when the Phoma sp. was grown on MEA amended with the non-ionic solute glycerol. Water activity and temperature and their interactions were
highly significant factors (P < 0.001) affecting growth of the Phoma sp., with optimum conditions of 0.998–0.980 a
w and 25 °C. Squalestatin production was similarly influenced by a
w, temperature, time and their interactions (P < 0.001). S1 and S2 production occurred over a narrower a
w and temperature range than growth, with a slightly lower optimum a
w range of 0.995–0.980 a
w. The optimum temperature for squalestatin production varied from 20 °C (S1) to 25 °C (S2) and yields of S2 were up to 1000
times lower than those of S1. The ratio of S1 and S2 produced by the Phoma sp. was influenced by a
w and temperature, with highest values at 0.99–0.98 a
w, and at 15 °C. Incubation times of 28 days gave highest yields of both S1 and S2. Up to 2000-fold increases in squalestatin
yields were measured at optimum environmental conditions, compared to the unmodified MEA. This indicates the need to consider
such factors in screening systems used to detect biologically active lead compounds produced by fungi.
Received: 2 June 1997 / Received last revision: 6 November 1997 / Accepted: 7 November 1997 相似文献
15.
Titis Wijayanto Hitoshi Wakabayashi Joo-Young Lee Nobuko Hashiguchi Mohamed Saat Yutaka Tochihara 《International journal of biometeorology》2011,55(4):491-500
The objective of this study was to investigate thermoregulatory responses to heat in tropical (Malaysian) and temperate (Japanese)
natives, during 60 min of passive heating. Ten Japanese (mean ages: 20.8 ± 0.9 years) and ten Malaysian males (mean ages:
22.3 ± 1.6 years) with matched morphological characteristics and physical fitness participated in this study. Passive heating
was induced through leg immersion in hot water (42°C) for 60 min under conditions of 28°C air temperature and 50% RH. Local
sweat rate on the forehead and thigh were significantly lower in Malaysians during leg immersion, but no significant differences
in total sweat rate were observed between Malaysians (86.3 ± 11.8 g m−2 h−1) and Japanese (83.2 ± 6.4 g m−2 h−1) after leg immersion. In addition, Malaysians displayed a smaller rise in rectal temperature (0.3 ± 0.1°C) than Japanese
(0.7 ± 0.1°C) during leg immersion, with a greater increase in hand skin temperature. Skin blood flow was significantly lower
on the forehead and forearm in Malaysians during leg immersion. No significant different in mean skin temperature during leg
immersion was observed between the two groups. These findings indicated that regional differences in body sweating distribution
might exist between Malaysians and Japanese during heat exposure, with more uniform distribution of local sweat rate over
the whole body among tropical Malaysians. Altogether, Malaysians appear to display enhanced efficiency of thermal sweating
and thermoregulatory responses in dissipating heat loss during heat loading. Thermoregulatory differences between tropical
and temperate natives in this study can be interpreted as a result of heat adaptations to physiological function. 相似文献
16.
A. Ancel L. Petter R. Groscolas 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(7):533-539
The triggering of transitory egg desertion in fasting and incubating blue petrels (Halobaena caerulea, nocturnal burrowing seabirds living in the subantarctic region) was investigated by continuously monitoring both body temperature
(T
sto) and egg temperature (T
egg) with a telemetry system, and by measuring body mass (BM) loss. The birds were kept captive in their burrow and incubated
day and night without any interruption; there was no day-night cycle in T
sto and T
egg, which averaged 39.9 °C and 32.0 °C, respectively. There was no evidence of hypothermia as a way to save energy in this fasting
situation. Egg desertion occurred at night and was an abrupt and definitive phenomenon reflected by a simultaneous fall in
T
egg and a peak in T
sto. After egg desertion, a distinct day-night cycle of body temperature was observed, T
sto being 0.6 °C higher during night-time (P < 0.05), probably reflecting increased nocturnal activity. BM at egg desertion averaged 166.7 ± 3.8 g in telemetered birds
and 164.4 ± 1.6 g in␣a group of free-living birds. Throughout fasting, the␣specific daily BM loss remained at 46 ± 1 g · kg−1 · day−1, but increased sharply below a critical BM of 160.0 ± 2.5 g. Thus, fasting incubating blue petrels spontaneously desert their
egg when reaching a BM threshold. This BM is very close to a critical value in fasting birds and mammals that corresponds
to a critical depletion of fat stores and to a shift from lipid to protein utilization. This strongly suggests that such a
metabolic shift triggers behavioural changes leading to egg desertion and refeeding, which is of great relevance to the understanding
of the long-term control of food intake and BM.
Accepted: 16 July 1998 相似文献
17.
I. Giladi B. Pinshow 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):311-318
Body water conservation is important in flying birds because the very high metabolic demands and heat dissipation requirements
during flight depend on plasma-volume integrity. Wind tunnel experiments and theoretical model predictions show that evaporative
water loss (EWL) depends on air temperature (T
a) and water vapor density (ρa), but these relationships have not been examined in free-flying birds. The contribution of excretory water loss to the total
water loss of a flying bird is thought to be negligible but this assumption is untested. To study the dependence of water
losses on environmental conditions in free-flying birds and to quantify the contribution of excretory water loss to total
water loss, we estimated evaporative and excretory water losses in 16 trained, free-flying tippler pigeons (Columba livia, 250–340 g). We collected excreta by attaching a light latex, water-impermeable receptacle around each bird's vent. By gravimetry,
we measured evaporative and excretory water losses of birds for eight flights at different T
as and compared flying to resting (control) birds for two of these flights. EWL was constant with respect to T
a when less than 15 °C, and increased with increasing T
a above 19 °C, indicating that evaporative cooling was invoked when the heat load increased. EWL increased with increasing
ρa, possibly due to the strong correlation between ρa and T
a. Excretory water loss was independent of ρa or T
a and averaged almost 10% of the total water loss. Measurements of EWL made on pigeons during wind tunnel experiments and previous
free-flight studies are consistent with our free-flight measurements made at similar T
a
s.
Accepted: 13 April 1999 相似文献
18.
Jeong-Beom Lee Jun-Sang Bae Takaaki Matsumoto Hun-Mo Yang Young-Ki Min 《International journal of biometeorology》2009,53(2):149-157
Natives of the tropics are able to tolerate high ambient temperatures. This results from their long-term residence in hot
and often humid tropical climates. This study was designed to compare the peripheral mechanisms of thermal sweating in tropical
natives with that of their temperate counterparts. Fifty-five healthy male subjects including 20 native Koreans who live in
the temperate Korean climate (Temperate-N) and 35 native tropical Malaysian men that have lived all of their lives in Malaysia
(Tropical-N) were enrolled in this study after providing written informed consent to participate. Quantitative sudomotor axon
reflex testing after iontophoresis (2 mA for 5 min) with 10% acetylcholine (ACh) was used to determine directly activated
(DIR) and axon reflex-mediated (AXR) sweating during ACh iontophoresis. The sweat rate, activated sweat gland density, sweat
gland output per single gland activated, and oral and skin temperature changes were measured. The sweat onset time of AXR
(nicotinic-receptor-mediated) was 56 s shorter in the Temperate-N than in the Tropical-N subjects (P < 0.0001). The nicotinic-receptor-mediated sweating activity AXR (1), and the muscarinic-receptor-mediated sweating activity
DIR, in terms of sweat volume, were 103% and 59% higher in the Temperate-N compared to the Tropical-N subjects (P < 0.0001). The Temperate-N group also had a 17.8% (P < 0.0001) higher active sweat gland density, 35.4% higher sweat output per gland, 0.24°C higher resting oral temperature,
and 0.62°C higher resting forearm skin temperature compared to the Tropical-N subjects (P < 0.01). ACh iontophoresis did not influence oral temperature, but increased skin temperature near where the ACh was administered,
in both groups. These results suggest that suppressed thermal sweating in the Tropical-N subjects was, at least in part, due
to suppressed sweat gland sensitivity to ACh through both recruitment of active sweat glands and the sweat gland output per
each gland. This physiological trait guarantees a more economical use of body fluids, thus ensuring more efficient protection
against heat stress. 相似文献
19.
F. Aujard M. Perret G. Vannier 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(7):540-548
The lesser mouse lemur, a small Malagasy primate, is exposed to strong seasonal variations in ambient temperature and food
availability in its natural habitat. To face these environmental constraints, this nocturnal primate exhibits biological seasonal
rhythms that are photoperiodically driven. To determine the role of daylength on thermoregulatory responses to changes in
ambient temperature, evaporative water loss (EWL), body temperature (T
b) and oxygen consumption, measured as resting metabolic rate (RMR), were measured in response to ambient temperatures ranging
from 5 °C to 35 °C, in eight males exposed to either short (10L:14D) or long (14L:10D) daylengths in controlled captive conditions.
In both photoperiods, EWL, T
b and RMR were significantly modified by ambient temperatures. Exposure to ambient temperatures below 25 °C was associated
with a decrease in T
b and an increase in RMR, whereas EWL remained constant. Heat exposure caused an increase in T
b and heat loss through evaporative pathways. Thermoregulatory responses to changes in ambient temperature significantly differed
according to daylength. Daily variations in T
b and EWL were characterized by high values during the night. During the diurnal rest, lower values were found and a phase
of heterothermia occurred in the early morning followed by a spontaneous rewarming. The amplitude of T
b decrease with or without the occurrence of torpor (T
b < 33 °C) was dependent on both ambient temperature and photoperiod. This would support the hypothesis of advanced thermoregulatory
processes in mouse lemurs in response to selective environmental pressure, the major external cue being photoperiodic variations.
Accepted: 4 August 1998 相似文献
20.
Two species of the genus Acomys coexist in arid zones of southern Israel. Acomys russatus is distributed in extremely arid areas, while A. cahirinus is common in both Mediterranean and arid regions. Individuals of both species from a rodent community in the Ein Gedi Nature
Reserve were implanted with temperature-sensitive transmitters. Body temperature (T
b) rhythms were recorded in free-ranging mice at four different seasons of the year. A. cahirinus (30–45 g) showed a nocturnal rhythm of T
b throughout the year. In the activity phase during the night T
b increased to 38.2°C. During the day T
b decreased to 34°C. This species displayed this pattern in summer also when ambient temperatures rose above T
b. The T
b of A. russatus (45–65 g) varied between 34.8 and 41°C during the hot season, showing a bimodal temperature rhythm with maximal values in
the morning and in the evening. Measurements of activity in this species showed inactivity during the hottest period of a
summer day. In winter A. russatus showed no clearly detectable diurnal or ultradian rhythm in T
b, which remained constant between narrow limits of 35.2 and 36.8°C.
Received: 21 December 1998 / Accepted: 15 March 1999 相似文献