The influence of dehydration on the thermal preferences of the Western tiger snake,<Emphasis Type="Italic"> Notechis scutatus</Emphasis>

Temperature selection in tiger snakes (Notechis scutatus) is strongly influenced by hydration state and this response varies between two distinct neighbouring populations on semi-arid Carnac Island and mainland wetland (Herdsman Lake). Fed and hydrated (control) Carnac Island snakes selected a preferred body temperature of 26.2+/-1.2 degrees C and an average maximum temperature of 32.5+/-0.5 degrees C in a photo-thermal gradient. Dehydrated Carnac Island snakes selected a significantly lower preferred body temperature (19.7+/-1.6 degrees C) and average maximum temperature (27.7+/-1.0 degrees C). Control Herdsman Lake snakes selected a preferred body temperature of 27.5+/-0.6 degrees C and an average maximum temperature of 33.3+/-0.4 degrees C. Dehydrated Herdsman Lake snakes selected a significantly lower preferred body temperature (23.3+/-1.1 degrees C) and a lower average maximum temperature (31.8+/-0.6 degrees C). Thermal depression (decreased preferred body and average maximum temperatures) in response to dehydration was greater for Carnac Island than Herdsman Lake snakes. As decreases in temperature and activity can reduce water loss, our laboratory data suggest that the survival of the relict population of tiger snakes on Carnac Island is associated with thermoregulatory modifications, which may have the effect of enhancing water conservation in this waterless habitat.     

Effects of fasting on thermoregulatory processes and the daily oscillations in rats

To investigate the mechanism involved in the reduction of body core temperature (T(core)) during fasting in rats, which is selective in the light phase, we measured T(core), surface temperature, and oxygen consumption rate in fed control animals and in fasted animals on day 3 of fasting and day 4 of recovery at an ambient temperature (T(a)) of 23 degrees C by biotelemetry, infrared thermography, and indirect calorimetry, respectively. On the fasting day, 1) T(core) in the light phase decreased (P < 0.05) from the control; however, T(core) in the dark phase was unchanged, 2) tail temperature fell from the control (P < 0.05, from 30.7 +/- 0.1 to 23.9 +/- 0.1 degrees C in the dark phase and from 29.4 +/- 0.1 to 25.2 +/- 0.2 degrees C in the light phase), 3) oxygen consumption rate decreased from the control (P < 0.05, from 24.37 +/- 1.06 to 16.24 +/- 0.69 ml. min(-1). kg body wt(-0.75) in the dark phase and from 18.91 +/- 0.64 to 14.00 +/- 0.41 ml. min(-1). kg body wt(-0.75) in the light phase). All these values returned to the control levels on the recovery day. The results suggest that, in the fasting condition, T(core) in the dark phase was maintained by suppression of the heat loss mechanism, despite the reduction of metabolic heat production. In contrast, the response was weakened in the light phase, decreasing T(core) greatly. Moreover, the change in the regulation of tail blood flow was a likely mechanism to suppress heat loss.     

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 +/- 3 kg, means +/- SD). The animals, housed in a climatic chamber at 23 degrees C, were exposed for nine days to a cyclic protocol with daytime heat (40 degrees C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 +/- 4% of body mass, and plasma osmolality had increased from 290 +/- 8 to 323 +/- 9 mmol/kg (P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 +/- 0.18 degrees C) than in euhydration (-0.05 +/- 0.14 degrees C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27 degrees C) and dehydration (39.14 degrees C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 +/- 0.31) than in euhydrated animals (0.87 +/- 0.11, P = 0.003). Return of drinking water at 39 degrees C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated.     

Sulfidogenic fluidized-bed treatment of metal-containing wastewater at low and high temperatures

The applicability of a fluidized-bed reactor (FBR)-based sulfate reducing bioprocess was investigated for the treatment of iron-containing (40-90 mg/L) acidic wastewater at low (8 degrees C) and high (65 degrees C) temperatures. The FBRs operated at low and high temperatures were inoculated with cultures of sulfate-reducing bacteria (SRB) originally enriched from arctic and hot mining environments, respectively. Ethanol was supplemented as carbon and electron source for SRB. At 8 degrees C, ethanol oxidation and sulfate reduction rates increased steadily and reached 320 and 265 mg/L.day, respectively, after 1 month of operation. After this point, the rates did not change significantly during 130 days of operation. Despite the complete ethanol oxidation and iron precipitation, the average sulfate reduction efficiency was 35 +/- 4% between days 30 and 130 due to the accumulation of acetate. At 65 degrees C, a rapid startup was observed as 99.9, 46, and 29% ethanol, sulfate, acetate removals, in respective order, were observed after 6 days. The feed pH was decreased gradually from its initial value of 6 to around 3.7 during 100 days of operation. The wastewater pH of 4.3-4.4 was neutralized by the alkalinity produced in acetate oxidation and the average effluent pH was 7.8 +/- 0.8. As in the low temperature FBR, acetate accumulated. Hence, the oxidation of acetate is the rate-limiting step in the sulfidogenic ethanol oxidation by thermophilic and psychrotrophic SRB. The sulfate reduction rate is three times and acetate oxidation rate is four times higher at 65 degrees C than at 8 degrees C.     

Equine sweating responses to submaximal exercise during 21 days of heat acclimation.

This study examined sweating responses in six exercise-trained horses during 21 consecutive days (4 h/day) of exposure to, and daily exercise in, hot humid conditions (32-34 degrees C, 80-85% relative humidity). On days 0, 3, 7, 14, and 21, horses completed a standardized exercise test on a treadmill (6 degrees incline) at a speed eliciting 50% of maximal O(2) uptake until a pulmonary artery temperature of 41.5 degrees C was attained. Sweat was collected at rest, every 5 min during exercise, and during 1 h of standing recovery for measurement of ion composition (Na(+), K(+), and Cl(-)) and sweating rate (SR). There was no change in the mean time to reach a pulmonary artery temperature of 41.5 degrees C (range 19.09 +/- 1.41 min on day 0 to 20.92 +/- 1.98 min on day 3). Peak SR during exercise (ml. m(-2). min(-1)) increased on day 7 (57.5 +/- 5. 0) but was not different on day 21 (48.0 +/- 4.7) compared with day 0 (52.0 +/- 3.4). Heat acclimation resulted in a 17% decline in SR during recovery and decreases in body mass and sweat fluid losses during the standardized exercise test of 25 and 22%, respectively, by day 21. By day 21, there was also a 10% decrease in mean sweat Na(+) concentration for a given SR during exercise and recovery; this contributed to an approximately 26% decrease in calculated total sweat ion losses (3,112 +/- 114 mmol on day 0 vs. 2,295 +/- 107 mmol on day 21). By day 21, there was a decrease in sweating threshold ( approximately 1 degrees C) but no change in sweat sensitivity. It is concluded that horses responded to 21 days of acclimation to, and exercise in, hot humid conditions with a reduction in sweat ion losses attributed to decreases in sweat Na(+) concentration and SR during recovery.     

Seasonal and daily changes in the capacity for nonshivering thermogenesis in the golden hamsters housed under semi-natural conditions

Nonshivering thermogenesis (NST) is a main source of heat for many small mammals. It undergoes seasonal changes, being the highest in winter and the lowest in summer. Such acclimatization can ensure winter survival for species living in moderate or cold climates. Nevertheless, not only seasonal, but also daily changes in the capacity for NST seem to be of great importance. In this study, the effects of season and time of day on the temperature of brown adipose tissue (T(BAT)), preferred ambient temperature (PT(a)) and activity after noradrenaline (NA) injections in golden hamsters (Mesocricetus auratus) housed under semi-natural conditions were investigated. Animals were kept in outdoor enclosures and experienced natural changes in both, photoperiod and ambient temperature (T(a)). NA-induced hyperthermia was the largest during autumn (mean increase in T(BAT) by 0.74+/-0.04 degrees C), while during summer increase in T(BAT) was similar to that recorded in control (saline-injected) animals (0.16+/-0.05 degrees C and 0.24+/-0.04 degrees C, respectively). In spring hyperthermia was intermediary (0.57+/-0.05 degrees C). Daily variations in the response to NA depended on the season. In summer, the largest increase in T(BAT) (0.45+/-0.1 degrees C) was recorded during the first part of the day, while in autumn-in the middle of the day and night (1.1+/-0.1 degrees C and 0.9+/-0.1 degrees C, respectively). In spring, all NA injections induced large increase in T(BAT) except for the injection in the middle of the night. The largest decrease in PT(a) after NA administration was recorded in autumn (mean decrease by 1.5+/-0.3 degrees C). Both, seasonal and daily changes in the capacity for NST reflect different demands for heat dependently on the time of the year and time of the day. It can be concluded that although long history of breeding in captivity, golden hamsters preserved ability to survive in natural environment.     

Sodium flux through the sodium channels of axon membrane fragments isolated from lobster nerves

The efflux of 22Na from vesicles formed by axolemma fragments isolated from lobster nerves was studied in the presence and in the absence of drugs having well-known action on the sodium channels. The vesicles were equilibrated 12-14 h at 4 degrees C with 22Na in lobster solution containing 1 mM ouabain. Afterwards the suspension was divided: one portion was used as control and the others were treated with veratrine (0.025-0.50 mg/ml), tetrodotoxin (1-2,000 nM) in the presence of veratrine, or tetrodotoxin alone. After 3 h at 20-22 degrees C, the suspensions were diluted into nonradioactive solutions and the 22Na efflux followed by a rapid filtration technique. The results revealed that veratrine increases the efflux rate and the additional application of tetrodotoxin abolishes it, e.g., 0.50 mg of veratrine/ml increases the rate, expressed in 10(-2) min(-1), from 0.59 +/- 0.04 (mean +/- SEM; n = 13) to 0.86 +/- 0.05 (n = 13), and the addition of 100 nM tetrodotoxin diminishes it to 0.48 +/- 0.07 (n = 4). This increase and diminution are statistically significant (P less than 0.005), but this is not the case between the control and the veratrine plus tetrodotoxin values (P greater than 0.05). 50% of the diminution is produced by 11.9 +/- 2.4 nM tetrodotoxin. Tetrodotoxin alone produces a slight diminution of the 22Na efflux. Batrachotoxin (0.50 muM) has an action similar to veratrine's. These findings are considered evidence of the presence of functioning sodium channels in the isolated axolemma fragments.     

Effect of thermoperiod on diapause intensity in Pyrrhocoris apterus (Heteroptera Pyrrhocoridae)

The intensity of adult diapause in Pyrrhocoris apterus was measured in two series of experiments as the duration of pre-oviposition period at a constant temperature of 25 degrees C after transfer from short (12L:12D) to long day conditions (18L:6D). Higher diapause intensity was induced with a thermoperiod than at constant temperatures. After the induction throughout larval instars 3-5 and during 4 weeks of adult life at short days and a thermoperiod of 25/15 degrees C the pre-oviposition period was 30+/-4 and 26+/-3 days. After induction at constant 25 degrees C the pre-oviposition period was 22+/-3 and 23+/-4 days, while after induction at constant 20 degrees C it was 17+/-4 and 19+/-4 days. Induction at a lower constant temperature of 20 degrees C was thus followed by a less intense diapause than the induction at a higher constant temperature of 25 degrees C. These counterintuitive results are discussed. The oxygen consumption rate measured at experimental temperatures prior to transfer from short to long days was higher at thermoperiodic conditions than at constant temperatures and it was similar at constant 20 and 25 degrees C. Thus, the oxygen consumption rate measured prior to the transfer was highest (indication of the least intense diapause) in the insects that showed later, after the transfer to long days, the longest pre-oviposition period (indication of the most intense diapause). Within the first two days after transfer to constant 25 degrees C, oxygen consumption rate measured at 25 degrees C decreased in the thermoperiodic insects, while it transiently increased in insects from constant 20 degrees C. Two days and later after the transfer, oxygen consumption rate was similar in all groups. Cold hardiness was not correlated with diapause intensity. The low lethal temperature in diapausing insects was correlated with the night temperature during diapause induction.     

The effects of temperature change on lung liquid production by in vitro lungs from fetal guinea pigs

Lungs from fetal guinea pigs of 58-65 days of gestation were supported in vitro for 3 h, and lung liquid production rates were measured by a dye dilution technique. In 36 control preparations, incubated continuously at 37 degrees C, the average production rate in the first hour was 1.46 +/- 0.23 ml/h per kg body weight; there was no significant change over the following two h. In 36 further preparations the temperature was changed during the middle hour (ABA), with the following % reductions in production rates: at -1 degrees C (relative to 37 degrees C), 68.2 +/- 17.1%; -2 degrees C, 125.5 +/- 30.1% (reabsorption); -3 degrees C, 103.8 +/- 32.8% (reabsorption); -5 degrees C, 82.7 +/- 16.6%, -8 degrees C, 94.7 +/- 1.8 %; +2 degrees C, 100.7 +/- 12.6% (all significant, P less than 0.025-0.005). Slow recoveries followed a return to starting conditions, except after the increase in temperature, 10(-6) M amiloride abolished reabsorption, but not depression, during the maximal effects of temperature reduction (at -2 degrees C, n = 6); amiloride had no effect on control preparations (n = 6). These results suggest that: (a) reductions of 2-3 degrees C, as seen in the delivery room, abolish secretion, but not reabsorption of lung fluid; larger reductions stop both processes; (b) the reabsorptions seen after a fall in temperature depend on Na(+)-transport mechanisms; (c) lung liquid production was sensitive to a rise in temperature, so that fevers might adversely affect lung development, and (d) the fall in temperature at birth may be an important factor in the early reabsorption of lung liquid.     

Temperature during the day, but not during the night, controls flowering of Phalaenopsis orchids

Phalaenopsis orchids are among the most valuable potted flowering crops commercially produced throughout the world because of their long flower life and ease of crop scheduling to meet specific market dates. During commercial production, Phalaenopsis are usually grown at an air temperature > or =28 degrees C to inhibit flower initiation, and a cooler night than day temperature regimen (e.g. 25/20 degrees C day/night) is used to induce flowering. However, the specific effect of day and night temperature on flower initiation has not been well described, and the reported requirement for a diurnal temperature fluctuation to elicit flowering is unclear. Two Phalaenopsis clones were grown in glass greenhouse compartments with constant temperature set points of 14, 17, 20, 23, 26, or 29 degrees C and fluctuating day/night (12 h/12 h) temperatures of 20/14, 23/17, 26/14, 26/20, 29/17, or 29/23 degrees C. The photoperiod was 12 h, and the maximum irradiance was controlled to < or =150 micromol m(-2) s(-1). After 20 weeks, > or =80% of plants of both clones had a visible inflorescence when grown at constant 14, 17, 20, or 23 degrees C and at fluctuating day/night temperatures of 20/14 degrees C or 23/17 degrees C. None of the plants were reproductive within 20 weeks when grown at a constant 29 degrees C or at 29/17 degrees C or 29/23 degrees C day/night temperature regimens. The number of inflorescences per plant and the number of flower buds on the first inflorescence were greatest when the average daily temperature was 14 degrees C or 17 degrees C. These results indicate that a day/night fluctuation in temperature is not required for inflorescence initiation in these two Phalaenopsis clones. Furthermore, the inhibition of flowering when the day temperature was 29 degrees C and the night temperature was 17 degrees C or 23 degrees C suggests that a warm day temperature inhibits flower initiation in Phalaenopsis.     

Control of local heat gain by vasomotor response of the hand

Finger blood flow (BF) was measured by venous occlusion plethysmography using mercury-in-Silastic strain gauges during immersion of one hand in hot water (raised by steps of 2 degrees C every 10 min from 35 to 43 degrees C), the other being a control (kept immersed in water at 35 degrees C). The measurements were made in three different thermal states on separate days: 1) cool-25 degrees C, 40% rh, esophageal temperature (Tes) = 36.64 +/- 0.10 degrees C; 2) warm-35 degrees C, 40% rh, Tes = 36.71 +/- 0.11 degrees C; and 3) hot-35 degrees C, 80% rh with the legs immersed in water at 42 degrees C, Tes = 37.26 +/- 0.11 degrees C. When water temperature was raised at 42 degrees C, Tes = 37.26 +/- 0.11 When water temperature was raised to 39-41 degrees C in the warm state, finger BF in the hand heated locally (BFw) decreased. When water temperature was raised to 43 degrees C, however, BFw returned to the control value. In the hot state, Tes rose steadily, reaching 37.90 +/- 0.12 degrees C at the end of the 50-min sessions. BF in the control finger also increased gradually during the session. BFw showed a tendency to decrease when water temperature was raised to 39 degrees C, but the change was not greater than that observed in the warm state. In the cool state, no such reduction in BFw was observed when water temperature was raised to 39-41 degrees C. On the contrary, BFw increased at water temperatures of 41-43 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypothermia versus torpor in response to cold stress in the native Australian mouse Pseudomys hermannsburgensis and the introduced house mouse Mus musculus

This study compared torpor as a response to food deprivation and low ambient temperature for the introduced house mouse (Mus musculus) and the Australian endemic sandy inland mouse (Pseudomys hermannsburgensis). The house mouse (mass 13.0+/-0.48 g) had a normothermic body temperature of 34.0+/-0.20 degrees C at ambient temperatures from 5 degrees C to 30 degrees C and a basal metabolic rate at 30 degrees C of 2.29+/-0.07 mL O2 g(-1) h(-1). It used torpor with spontaneous arousal at low ambient temperatures; body temperature during torpor was 20.5+/-3.30 degrees C at 15 degrees C. The sandy inland mouse (mass 11.7+/-0.16 g) had a normothermic T(b) of 33.0+/-0.38 degrees C between T(a) of 5 degrees C to 30 degrees C, and a BMR of 1.45+/-0.26 mL O2 g(-1) h(-1) at 30 degrees C. They became hypothermic at low T(a) (T(b) about 17.3 degrees C at T(a)=15 degrees C), but did not spontaneously arouse. They did, however, survive and become normothermic if returned to room temperature (23 degrees C). We conclude that this is hypothermia, not torpor. Consequently, house mice (Subfamily Murinae) appear to use torpor as an energy conservation strategy whereas sandy inland mice (Subfamily Conilurinae) do not, but can survive hypothermia. This may reflect a general phylogenetic pattern of metabolic reduction in rodents. On the other hand, this may be related to differences in the social structure of house mice (solitary) and sandy inland mice (communal).     

Heat debt as an index for cold adaptation in men

Several types of cold adaptation in men have been described in the literature (metabolic, insulative, hypothermic). The aim of this study is to show that the decrease of heat debt can be considered as a new index for cold adaptation. Ten male subjects were acclimated by water immersions (temperature 10-15 degrees C, 4 immersions/wk over 2 mo). Thermoregulatory responses before and after acclimation were tested by a standard cold test in a climatic chamber for 2 h at rest [dry bulb temperature (Tdb): 10 degrees C; relative humidity (rh): 25%]. After adaptation, four thermoregulatory modifications were observed: an increase in the delay for the onset of shivering (32.7 +/- 7.99 instead of 14.1 +/- 5.25 min); a decrease of body temperature levels for the onset of shivering [rectal temperature (Tre): 37.06 +/- 0.08 instead of 37.31 +/- 0.06 degrees C; mean skin temperature (Tsk): 24.83 +/- 0.56 instead of 26.86 +/- 0.46 degrees C; mean body temperature (Tb): 33.03 +/- 0.20 instead of 34.16 +/- 0.37 degrees C); a lower level of body temperatures in thermoneutrality (Tre = 37.16 +/- 0.08 instead of 37.39 +/- 0.06 degrees C; Tsk = 31.29 +/- 0.21 instead of 32.01 +/- 0.22 degrees C; Tb = 35.92 +/- 0.08 instead of 36.22 +/- 0.05 degrees C); a decrease of heat debt calculated from the difference between heat gains and heat losses (5.66 +/- 0.08 instead of 8.33 +/- 0.38 kJ/kg). The different types of cold adaptation observed are related to the physical characteristics of the subjects (percent body fat content) and the level of physical fitness (VO2max).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cutaneous and subcutaneous blood flow during general anaesthesia

The vasodilator effect of anaesthetic agents on cutaneous vessels has often been investigated. In contrast, although subcutaneous tissue is concerned with metabolism and thermoregulation, the effects of anaesthesia on subcutaneous blood flow have not been well documented. The purpose of this study was to determine the magnitude of changes in cutaneous and subcutaneous blood flow during general anaesthesia in Man. Anaesthesia was induced with flunitrazepam in 15 patients before facial plastic surgery. Blood flow was estimated using heat thermal clearance (HC). Two HC sensors in different areas allowed the measurement of superficial and deep HC. Systolic (SABP), diastolic (DABP) and mean arterial blood pressure (MABP), heart rate (HR), and rectal and mean skin temperature were also recorded. After induction of anaesthesia, HR increased significantly (p less than 0.05) whereas SABP, DABP and MABP remained unchanged. The rectal-toe temperature gradient fell from 6.3 +/- 4.1 degrees C to 3.4 +/- 1.1 degrees C (p less than 0.01) suggesting a reduction in vasomotor tone. Superficial HC increased from 0.37 +/- 0.06 to 0.42 +/- 0.08 W.m-1.degrees C-1 (p less than 0.05) whereas deep HC decreased from 0.33 +/- 0.07 to 0.31 +/- 0.09 W.m-1.degrees C-1 (NS) and returned to the control value thereafter. Rectal temperature and mean skin temperature were unchanged. The changes in deep HC are similar to those previously observed in muscle during induction of anaesthesia. Our results show that anaesthesia mainly affects cutaneous blood flow, without any significant change in subcutaneous blood flow during the early phase of anaesthesia in human beings.     

Behavioral thermoregulation by hypoxic rats.

To address whether a shift in hypothalamic thermal setpoint might be a significant factor in induction of hypoxic hypothermia, behavioral thermoregulation was examined in 7 female Sprague-Dawley rats implanted with radiotelethermometers for deep body temperature (Tb) measurement in a thermocline during normoxia (PO2 = 125 torr) and hypoxia (PO2 = 60 torr). Normoxic rats (TNox) selected a mean ambient temperature of 19.7 +/- 1.4 (SE) degrees C and maintained Tb at 37.0 +/- 0.2 degrees C. Hypoxic rats selected a significantly higher ambient temperature (THox = 28.6 +/- 2.2 degrees C) but maintained Tb significantly lower at 35.5 +/- 0.3 degrees C. Without a thermal gradient (ambient temperature = 25 degrees C), Tb during hypoxia was 35.4 +/- 0.4 degrees C. The maintenance of a lower body temperature during hypoxia through behavioral thermoregulation despite having warmer temperatures available supports the hypothesis that the thermoregulatory setpoint of hypoxic rats is shifted to promote thermoregulation at a lower Tb, effectively reducing oxygen demand when oxygen supply is limited.     

The development of homeothermy in mink (Mustela vison)

In mink (Mustela vison) kits newborn mortality is very high. One of the major causes of death is hypothermia. The objectives of this study were to observe the development of thermoregulation in mink kits, and their ability to maintain their body temperature during the postnatal period (1-50 days of age). Based on the kit's body weight (BW), and rectal and ambient temperature measurements during cold (+4 degrees C) and warm (+40 degrees C) exposures, a homeothermy index (HI) and cooling and warming rates were calculated. No significant differences in the body temperatures were found between the kits and the dam after 36 days of age. The kits were able to maintain homeothermy by 22 days of age (HI 90%). The body cooling rate was 0.88+/-0.04 degrees C min(-1) on day 1 but only 0.35+/-0.03 degrees C min(-1) at 22 days of age. The body WR was lower: day 1, 0.85+/-0.04 degrees C min(-1) and 0.22+/-0.03 degrees C min(-1) at 22 days of age. All measured and calculated thermophysiological variables were significantly influenced by BW and age of the kit.     

Effect of temperature on the development and viability of Gryon gallardoi (Brethes) (Hymenoptera: Scelionidae) parasitizing Spartocera dentiventris (Berg) (Hemiptera: Coreidae) eggs.

The development and viability of Gryon gallardoi (Brethes) (Hym.: Scelionidae) in Spartocera dentiventris (Berg) (Hem.: Coreidae) eggs were studied under four temperatures: 15, 20, 25, and 30 +/- 1 degree C, with a 12-h photophase. No parasitoid developed at 15 degrees C. Otherwise, viability reached 98.8% without varying significantly over the temperature range tested. The duration of development for males and females was inversely proportional to the temperature increase, varying respectively from 46.2 +/- 0.13 and 47.1 +/- 0.11 days (20 degrees C) to 13.3 +/- 0.07 and 13.4 +/- 0.06 days (30 degrees C). Males developed faster than females. The values estimated for the lowest thermic thresholds of development and the thermic constants were 15.5 degrees C and 185.19 DD for males and 15.6 degrees C and 192.31 DD for females, respectively. Given the average weather conditions in Porto Alegre, RS (30 degrees 01' S and 51 degrees 13' W), Brazil, G. gallardoi could annually produce 8.54 and 8.07 generations of males and females, respectively. The low rates of parasitism observed in the field during the first generation of its host may be due to the small number of G. gallardoi generations in this period.     

Turnover of rod photoreceptor outer segments. I. Membrane addition and loss in relationship to temperature

Membrane turnover in outer segments of Rana pipiens red rods (ROS) was studied in tadpoles maintained under cyclic lighting (12L:12D) at 23 degrees, 28 degrees, and 33 degrees C. Large fragments (greater than 2 microns in diameter or length) were shed from the ROS tips shortly after the onset of light. These were phagocytized by the pigment epithelium (PE) which caused an increase in the number of phagosomes greater than 2 microns in size (large phagosomes). Large phagosomes were present in highest numbers 2-4 h after light exposure and were degraded by 8-12 h. The proportion of ROS that shed each day after the onset of the light cycle increased with increment increases in temperatures (23 degrees C-18%, 28 degrees C-33%, 33 degrees C-42% per day), resulting, in a reduction in the average interval of time between repeated sheddings (23 degrees C-5.6 days, 28 degrees C-3 days, 33 degrees C-2.4 days) though the average numbers of disks shed from ROS at the various temperatures were not significantly different (23 degrees C-139.5 +/- 5.7, 28 degrees C-129.4 +/- 7.6, 33 degrees C-129.9 +/- 4.8 disks/shed packet). Phagosomes in the PE that were less than 2 microns in diameter (small phagosomes) were present in relatively constant numbers throughout the day, and their numbers increased at higher temperatures. The absence of a concomitant increase in small phagosomes as large phagosomes were degraded indicates that large phagosomes were not the major source of small phagosomes. When the PE was isolated to culture in the absence of the retina, these small phagosomes were degraded. The rate of disk addition to the ROS base was determined by autoradiography after [3H]leucine injection. The number of disks added per day increased with elevations of temperature (23 degrees C-32.4; 28 degrees C-55.9; 33 degrees C-65.5). The average number of disks added to the ROS between repeated sheddings (23 degrees C-181.4; 28 degrees C-167.7; 33 degrees C-157.2) was greater than the number of disks shed after light exposure. Inasmuch as the ROS show no net increase in length during the tadpole stages utilized, the remaining disks must be lost at some other time. Electron microscope analysis revealed the presence of small groups of disks in curled configurations at the tips of ROS, suggesting possible stages of detachment.(ABSTRACT TRUNCATED AT 400 WORDS)     

The influence of whole-body vs. torso pre-cooling on physiological strain and performance of high-intensity exercise in the heat

Little research has been reported examining the effects of pre-cooling on high-intensity exercise performance, particularly when combined with strategies to keep the working muscle warm. This study used nine active males to determine the effects of pre-cooling the torso and thighs (LC), pre-cooling the torso (ice-vest in 3 degrees C air) while keeping the thighs warm (LW), or no cooling (CON: 31 degrees C air), on physiological strain and high-intensity (45-s) exercise performance (33 degrees C, 60% rh). Furthermore, we sought to determine whether performance after pre-cooling was influenced by a short exercise warm-up. The 45-s test was performed at different (P<0.05) mean core temperature [(rectal+oesophageal)/2] [CON: 37.3+/-0.3 (S.D.), LW: 37.1+/-0.3, LC: 36.8+/-0.4 degrees C] and mean skin temperature (CON: 34.6+/-0.6, LW: 29.0+/-1.0, LC: 27.2+/-1.2 degrees C) between all conditions. Forearm blood flow prior to exercise was also lower in LC (3.1+/-2.0 ml 100 ml tissue(-1) x min(-1)) than CON (8.2+/-2.5, P=0.01) but not LW (4.3+/-2.6, P=0.46). After an exercise warm-up, muscle temperature (Tm) was not significantly different between conditions (CON: 37.3+/-1.5, LW: 37.3+/-1.2, LC: 36.6+/-0.7 degrees C, P=0.16) but when warm-up was excluded, T(m) was lower in LC (34.5+/-1.9 degrees C, P=0.02) than in CON (37.3+/-1.0) and LW (37.1+/-0.9). Even when a warm-up was performed, torso+thigh pre-cooling decreased both peak (-3.4+/-3.8%, P=0.04) and mean power output (-4.1+/-3.8%, P=0.01) relative to the control, but this effect was markedly larger when warm-up was excluded (peak power -7.7+/-2.5%, P=0.01; mean power -7.6+/-1.2%, P=0.01). Torso-only pre-cooling did not reduce peak or mean power, either with or without warm-up. These data indicate that pre-cooling does not improve 45-s high-intensity exercise performance, and can impair performance if the working muscles are cooled. A short exercise warm-up largely removes any detrimental effects of a cold muscle on performance by increasing Tm.     

Possible biphasic sweating response during short-term heat acclimation protocol for tropical natives

The aim of the present study was to evaluate the sweat loss response during short-term heat acclimation in tropical natives. Six healthy young male subjects, inhabitants of a tropical region, were heat acclimated by means of nine days of one-hour heat-exercise treatments (40+/-0 degrees C and 32+/-1% relative humidity; 50% (.)VO(2peak) on a cycle ergometer). On days 1 to 9 of heat acclimation whole-body sweat loss was calculated by body weight variation corrected for body surface area. On days 1 and 9 rectal temperature (T(re)) and heart rate (HR) were measured continuously, and rating of perceived exertion (RPE) every 4 minutes. Heat acclimation was confirmed by reduced HR (day 1 rest: 77+/-5 b.min(-1); day 9 rest: 68+/-3 b.min(-1); day 1 final exercise: 161+/-15 b.min(-1); day 9 final exercise: 145+/-11 b.min(-1), p<0.05), RPE (13 vs. 11, p<0.05) and T(re) (day 1 rest: 37.2+/-0.2 degrees C; day 9 rest: 37.0+/-0.2 degrees C; day 1 final exercise: 38.2+/-0.2 degrees C; day 9 final exercise: 37.9+/-0.1 degrees C, p<0.05). The main finding was that whole-body sweat loss increased in days 5 and 7 (9.49+/-1.84 and 9.56+/-1.86 g.m(-2).min(-1), respectively) compared to day 1 (8.31+/-1.31 g.m(-2).min(-1), p<0.05) and was not different in day 9 (8.48+/-1.02 g.m(-2).min(-1)) compared to day 1 (p>0.05) of the protocol. These findings are consistent with the heat acclimation induced adaptations and suggest a biphasic sweat response (an increase in the sweat rate in the middle of the protocol followed by return to initial values by the end of it) during short-term heat acclimation in tropical natives.