Expression of angiotensin type 1 and 2 receptors in brain after transient middle cerebral artery occlusion in rats

Angiotensin II (Ang II) type 2 receptors (AT2Rs) have been associated with apoptosis. We hypothesized that AT2Rs are increased in stroke and may contribute effects of stroke to the brain. To test this, we have examined the expression of Ang II type 1 receptor (AT1R), AT2R and Ang II levels in the brain 24 h after transient middle cerebral artery occlusion (MCAO). The densities of AT1R and AT2R were measured by quantitative autoradiography (n=6). The levels of Ang II were measured by radioimmunoassay (RIA) (n=6) and by immunohistochemistry (n=3). AT1R levels on autoradiography showed a significant decrease (0.87±0.06 to 1.39±0.07 fmol/mg, p<0.01) in the ventral cortex of the stroke side compared to the cortices of non-stroke (NS) rats (n=4). There was no significant difference on ATIR in the contralateral verbal cortex of the stroke rats compared to NS control. In contrast, levels of AT2R in the ventral cortex of both the stroke and the contralateral sides were significantly increased (0.77±0.06, p<0.05 and 0.91±0.05, p<0.01 compared to 0.60±0.03 fmol/mg tissue, respectively). RIA showed that Ang II in the ventral cortex of both the stroke and the contralateral sides were significantly increased (241.63±47.72, p<0.01 and 165.51±42.59, p<0.05 compared to 76.80±4.10 pg/g tissue, respectively). Also, Ang II in the hypothalamus was significantly increased (179.50±17.49 to 118.50±6.65 pg/g tissue, p<0.05). Immunohistochemistry confirmed the increase of Ang II. These results demonstrate that brain Ang II and AT2Rs are increased whereas AT1Rs are decreased after transient MCAO in rats. We conclude that in stroke, Ang II and AT2R are activated and may contribute neural effects to brain ischemia.     

Effect of nifedipine on core cooling in rats during tail cold water immersion

Male rats (450 g, n=11/group) were heated at an ambient temperature of 42°C until a rectal temperature of 42.8°C was attained. Rats, then received either saline (30°C)+tail ice water immersion (F+I) or saline (30°C)+tail ice water immersion+Nifedipine, a peripheral vasodilator, (F+I+N) to determine cooling rate effectiveness and survivability. The time to reach a rectal temperature of 42.8°C averaged 172 min in both groups resulting in similar heating rates (0.029°C/min). The cooling rates in group F+I and F+I+N were not significantly different from each other. We conclude that since Nifedipine did not improve cooling rates when combined with fluid+tail ice water immersion, its use as a cooling adjunct does not seem warranted.     

Daily rhythms of oxygen consumption, body temperature, activity and melatonin in the Norwegian lemming Lemmus lemmus under northern summer photoperiod

Rodents inhabiting high latitudes, close to the Arctic Circle or above it, are exposed to near 24 h daylight during the summer season. An example to such rodent species is the Norwegian lemming Lemmus lemmus, which is distributed in northern Fennoscandia. We measured daily rhythms of heat production (VO₂), body temperature (T_b), motor activity and melatonin secretion (measured from its metabolite 6-sulfatoximelatonin 6-SMT) in individuals exposed to natural day light, Oulu Finland, in August 1997 and at a controlled ambient temperature of 22 °C. Our results show a daily rhythm of VO₂ with an acrophase at 04:00 h and minimal values measured at 16:00 h, with a significant difference (p<0.001) between mean day and night values. 6-SMT also shows a daily rhythm with maximal secretion during the dark phase 24:00 and 06:00 h in which total 6-SMT values were 2.92±1.1 and 3.87±1.2 ng, respectively. The lowest values were recorded at 12:00 h; 0.86±0.63 ng. These results suggest that lemmings show a VO₂ and melatonin daily rhythms, which seem to correlate with each other and it appears that melatonin secretion increases heat production.     

Determination of the thermodynamics of carbonic anhydrase acid-unfolding by titration calorimetry

The enthalpy of unfolding (Δ_uH) of carbonic anhydrase II was determined by titrating the protein with acid and measuring the heat using isothermal titration calorimetry (ITC) in the temperature range of 5 to 59 °C. By combining the ITC results with our previous findings by differential scanning calorimetry (DSC) in the temperature range of 39 to 72 °C, the Δ_uH dependence over a wide temperature range was obtained. The temperature dependence of the enthalpy displays significant curvature indicating that the heat capacity of unfolding (Δ_uC_p) is dependent on temperature. The T-derivative of Δ_uC_p was equal to 100 ± 30 J/(mol × K²), with the result that the Δ_uC_p is equal to 15.8 kJ/(mol × K) at 5 °C, 19.0 kJ/(mol × K) at 37 °C and 21.8 kJ/(mol × K) at 64 °C. The enthalpy of unfolding is zero at 17 °C. At lower temperatures, the Δ_uH becomes exothermic.

This method of determining protein unfolding thermodynamics using acid-ITC, significantly widens the accessible T-range, provides direct estimate of the thermodynamic parameters at physiological temperature, and gives further insight into the third T-derivative of the Gibbs free energy of unfolding.     

Attenuated feeding responses to circadian and palatability cues in mice lacking neuropeptide Y

Neuropeptide Y (NPY) is a potent orexigenic peptide that is implicated in the feeding response to a variety of stimuli. The current studies employed mice lacking NPY (Npy−/−) and their wild-type (Npy+/+) littermates to investigate the role of this peptide in the feeding response to circadian and palatability cues. To investigate the response to a circadian stimulus, we assessed food intake during the 4-h period following dark onset, a time of day characterized by maximal rates of food consumption. Compared to Npy+/+ controls, intake of Npy−/− mice was reduced by 33% during this period (0.6 ± 0.1 g versus 0.9 ± 0.1 g; p ≤ 0.05). In contrast, intake did not differ between genotypes when measured over a 24-h period (3.7 ± 0.2 g versus 3.5 ± 0.3 g; p = ns). Furthermore, reduced dark cycle 4 h food intake in Npy−/− mice was not evident after a 24-h fast (1.4 ± 0.1 g for both genotypes; p = ns), despite a pronounced delay in the initiation of feeding (636 ± 133 s versus 162 ± 29 s; p ≤ 0.05). To investigate the role of NPY in the feeding response to palatability cues, mice were presented with a highly palatable diet (HP) for 1 h each day (in addition to having ad libitum access to chow) for 18 days. Npy+/+ mice rapidly increased daily HP intake such that by the end of the first week, they derived a substantial fraction of daily energy from this source (41 ± 3%). By comparison, HP intake was markedly reduced in Npy−/− mice during the first week (24 ± 7% of daily energy intake, p ≤ 0.05 versus Npy+/+), although it eventually increased (by Day 9) to values comparable to those of Npy+/+ controls. These experiments suggest that NPY contributes to the mechanism whereby food intake increases in response to circadian and palatability cues and that mechanisms driving food intake in response to these stimuli differ from those activated by energy restriction.     

Changes in denaturation and rheological properties of collagen-hyaluronic acid scaffolds as a result of temperature dependencies

This report describes the effect of temperature on the mechanical viscoelastic properties such as: storage modulus (E′), loss modulus (E″), and loss tangent (tan δ) of the collagen sponges modified with hyaluronic acid (HA). In order to detect collagen–HA copolymer denaturation and to assess its thermal stability, the differential scanning calorimetry (DSC) supplemented by thermogravimetric (TG) measurements was used. The denaturation temperature (T_d) of unmodified collagen samples increased from 69 to 86 °C for cross-linked samples, respectively. These temperature dependencies show remarkable changes in E′ and E″ at selected temperature up to 226 °C for all samples due to the release of loosely and strongly bound water. The influence of HA on the viscoelastic behavior of collagen is manifested by a shift of the tan δ peak associated with the process of decomposition towards higher temperatures resulting in a higher thermo-stability of the modified scaffolds.     

Daily rhythms of nonshivering thermogenesis and responses to photoperiod manipulations in Apodemus mystacinus from two different ecosystems

Comparative physiology is an important tool for understanding adaptation to environment. Regulatory nonshivering thermogenesis (NST) is an essential mechanism in small mammals for coping with low ambient temperatures. Because of its geographical location and its sharp climatic changes across short distances, Israel offers conducting comparative studies between different populations of the same species. The aims of this study were: (1) to compare NST-capacity daily rhythms, between the two populations of the broad-toothed field mouse Apodemus Mystacinus—that of Mount Carmel (Mediterranean) and that of Mount Hermon (Subalpinic), (2) to compare the thermoregulatory daily rhythms response to photoperiod manipulations of mice from the two populations.

Mice were acclimated for at least 3 weeks to long scotophase (16D:8L-LS) and then to long photophase (16L:8D-LP) at a constant ambient temperature (T_a) of 24±1 °C. The following variables were compared at four different times of the day (06, 12, 18, 24 h): minimal body temperature (T_bMin), minimal oxygen consumption (VO₂Min) measured at the lower critical point and their response to noradrenaline (NA), 1.5 mg/1 kg.W_b injected s.c., (VO₂NA and T_bNA). NST-capacity was calculated as the ratio between VO₂NA and VO₂Min. The measurements were carried out at T_a of 28 °C and in light conditions matching those of acclimation. NA was injected after establishing VO₂Min and T_bMin. The values mean±SD are given for each measurement for n=6.

A three-way ANOVA revealed a significant difference between the two populations. Significant differences were revealed at different hours within populations under the different photoperiod regimes for different measured variables.     

A miniswine model of heatstroke

We developed a miniswine model of passive heatstroke, in part, to explain the variable hyper-, normo- and hypokalemia seen in heatstroke victims. After a baseline period (T_amb=26–27°C), anesthetized and instrumented miniswine (n=13, mass=44.6 kg) were ramped to 41–43°C, 60% RH; 13 controls were treated identically, but T_re was maintained at 38°C. T_re of the experimental miniswine rose nearly linearly to 45–46°C until death (approx. 4 h). The response patterns of mean arterial pressure, heart rate, plasma K⁺, LPS, Ca²⁺, inorganic phosphate, lactate and a variety of other clinical chemical and physiological variables were determined. An explanation for the variability of plasma K⁺ in heatstroke victims was proposed. This model may be useful in characterizing the multisystemic pathology of severe heat injury and be useful for assessing innovative therapeutic regimens.     

Peripheral insulin administration attenuates the increase in neuropeptide Y concentrations in the hypothalamic arcuate nucleus of fasted rats

Fasting increases neuropeptide Y (NPY) concentrations in the arcuate nucleus (ARC), its site of synthesis, and in other regions of the rat hypothalamus. Neuropeptide Y is a potent central orexigenic agent and may therefore stimulate appetite during fasting. We tested the hypothesis that low plasma insulin levels stimulate ARC levels of NPY in fasted rats. Compared with freely fed controls (n = 8), rats fasted for 72 h (n = 8) showed significantly lower plasma insulin levels (28.9 ± 1.6 vs. 52.6 ± 5.7 pmol/l; p < 0.001) and higher ARC NPY concentrations (14.2 ± 1.8 vs. 8.4 ± 2.2 fmol/μg protein; p < 0.001). Fasted rats treated with subcutaneous insulin (5 U/kg/day; n = 10), which nearly normalized plasma insulin (46.6 ± 2.8 pmol/l), showed intermediate ARC NPY levels (11.2 ± 1.4 fmol/μg protein; p < 0.01 vs. controls and untreated fasted rats). Insulin administered peripherally, therefore, attenuates fasting-induced NPY increases in the ARC, supporting the hypothesis that hypoinsulinemia stimulates hypothalamic NPY.     

Critical thermal maximum and body water loss in first instar larvae of three Cetoniidae species (Coleoptera)

Critical thermal maximum (CT_max) and body water losses were measured in first instar larvae of Gnorimus nobilis, Osmoderma eremita (Trichiinae) and Cetonischema aeruginosa (Cetoniinae) when air temperature was increased gradually (0.5 °C/min) from 20 °C to the critical thermal maximum (CT_max), in dry air (near 0% R.H.).

The CT_max was significantly lower in O. eremita (45.6±0.7 °C) than in G. nobilis (48.5±0.6) and C. aeruginosa (51.4±0.9 °C).

An increase of 10 °C (30–40 °C) induced a 2-fold increase of the water loss in C. aeruginosa and O. eremita (Q₁₀=2.10±0.12 and 2.13±0.20, respectively). In the range from 40 to 45 °C to CT_max a strong increase of the water loss was observed in O. eremita and C. aeruginosa, respectively. Body water losses were significantly lower in C. aeruginosa than in O. eremita and G. nobilis over the range 20 °C—CT_max; no significant difference occurred between G. nobilis and O. eremita.     

Thermoregulation by the short-horned lizard (Phrynosoma douglassi) at high elevation

The short-horned lizard Phrynosoma douglassi was studied in a montane habitat (elevation of 2290 m) in the Guadalupe Mountains of Texas. The body temperatures (T_b) of active lizards were consistently between 35–36°C (grand mean=35.5°C) in the period from 0900 to 1800 h during the months of May through September. The lizards began their spring activity during April when environmental temperatures were still low. Although T_bs in April were significantly lower than during May through September, on sunny April days the lizards were able to maintain T_bs near 30°C even when air temperatures were as low as 1.5°C. P. douglassi at this site thermoregulated very effectively whenever they were not limited by the physical environment.     

Effects of oven- or freeze-drying on chemical composition and NIR spectra of pasture silage

In order to assess effects of drying method on chemical composition and NIR spectra of pasture silage, 20 samples of silages from permanent pastures of different qualities were subsampled and dried either by forced draught oven at 65°C or freeze-dried. Samples were analysed for crude protein (CP), crude fibre (CF), neutral detergent fibre (NDF), acid detergent fibre (ADF), gross energy (GE) and in vitro digestible organic matter in the dry matter (DOMD) and composition expressed on a dry-matter (DM) basis, either obtained as oven 105°C DM (DM_105°) or toluene DM (DM_tol). Effects of the drying method on chemical composition were estimated by paired comparisons. Near-infrared reflectance (NIR) spectra were taken and the difference spectra between treatments for each sample were plotted in order to visually inspect effects of treatments, either as log 1/R or transformed by their first derivative. Principal components explaining spectral variability were computed and samples graphically displayed according to the eigenvalues of the first (1 and 2), or second (2 and 3) pairs of principal components. Oven-drying resulted in a reduction in CP (p<0.02) content and an increase in CF (p<0.1), NDF (p<0.001) and ADF (p<0.06) content of silages, when expressed on a DM_105° basis. When expressed on a DM_tol basis, a reduction in CP (p<0.02) and DOMD (p<0.06) content was observed with oven drying, but fibre fractions were not affected (p>0.1). Effects of the drying treatment were visually apparent on NIR spectra when plotted as log 1/R against wavelengths, mainly as a baseline shift. Difference spectra (OD − FD), both as log 1/R and its first derivative, showed consistent absorption bands, indicative of different molecular responses of OD and FD silages to incident light. Plotting samples according to eigenvalues of the first two or second two principal components suggests that drying methods affect the distribution of samples. This is also indicative of an effect of drying treatment on spectral features and reinforces the general advice that sample processing should be consistent in order to avoid adding errors to NIR analysis.     

Responses of core and peripheral temperatures to chronic cold stress in transiently goitrous goats

Thyroid hormones play a major role in controlling basal metabolic rate, body temperature and hemodynamics. Responses of core and peripheral body temperatures to transient use of thyreostatic drugs are seldom measured simultaneously under chronic experimental settings. We developed a technique to attain this goal. Eighteen Damascus goat kids (initial Avg. BW=44±0.7 kg) underwent a minor invasive surgical procedure to implant two miniature temperature data loggers, intraperitoneally and subcutaneously, to assess core (T_core) and subcutaneous (T_sq) temperature changes when subjected to chronic (47 days) cold (< 10 °C) environment along with or without oral administration of the reversible goitrogen 6-N-propyl-2-thiouracil (PTU; 20 mg/kg BW/day). Nine animals served as controls whereas the remaining nine were treated with PTU for 31 out of total 47-day trial period. The PTU treatment significantly (P<0.05) depressed circulating free thyroxine (FT4), followed by a rebound after termination. Prior to initiation of PTU treatment, all animals displayed similar daily means of T_core and T_sq. Subsequently, both temperatures precipitously declined (P<0.01) with the gradual drop in ambient temperature (T_a) overtime. However, PTU caused an immediate and further drop in T_sq, suggesting a reduction in cutaneous perfusion. Interestingly, on the other hand, a delayed downregulation of T_core by PTU occurred 14 days post-treatment, indicating a relatively slower depression in metabolic thermogenesis after suppression of circulating thyroxine. Upon termination of PTU, T_core but not T_sq, returned to simulate control levels. Results from the current study show the practicality of our technique to concurrently record core and peripheral temperatures in chronically-instrumented animals, and that PTU causes a marked depression in thermoregulatory ability during cold stress with no indication for a reduction in the temperature set-point.     

A method to reduce the invasiveness of fetal catheterization in the cow

Surgical intervention in general anesthesia (GA) of the cow in late gestation is a stressful condition for both mother and fetus, potentially leading to premature delivery or fetal death. The present study hypothesized that fetal catheterization at days 246–253 (90% of gestation) is done with less physical and metabolic stress for the mother and fetus, when the surgery is performed on a standing cow and local anesthesia (LA) rather than on a recumbent cow in general anesthesia. Fetal and uterine maternal intra-vascular catheters were implanted during general anesthesia (GA, n=24) or local analgesia (LA, n=7). Blood gases and metabolite levels in the fetal calves and their mothers were measured during surgery and for 5 days post-operatively. During surgery, venous blood pH was higher (7.44±0.01 versus 7.39±0.01, P<0.05) and hemoglobin and oxygen contents lower in LA cows compared with GA cows (9.3±0.3 mg/dl versus 11.8±0.2 mg/dl, P<0.001 and 10.1±0.3 ml/dl versus 12.6±0.6 ml/dl, P<0.05). The differences between the two groups of fetuses reflected those of their dams in that LA fetuses showed lower arterial oxygen pressure (18.3±1.4 mmHg versus 24.8±1.4 mmHg, P<0.05) and hemoglobin (7.81±0.30 mg/dl versus 9.22±0.21 mg/dl P<0.01) and furthermore, they also showed higher blood glucose (2.4±0.2 mM versus 1.4±0.1 mM, P<0.01). During the 5 days post-surgery, 10 GA fetuses (42%) and 1 LA fetus (14%) died in utero. Bacterial contamination was implicated in six of the GA deaths and in the one LA death. In the dams with surviving calves, differences in hemoglobin (9.49±0.21 mg/dl versus 11.17±0.23 mg/dl P<0.001) and O₂ct (10.9±0.3 ml/dl versus 12.5±0.5 ml/dl, P<0.05) were still present, and in addition, blood glucose was higher in LA versus GA cows (4.3±0.2 mM versus 3.8±0.1 mM, P<0.05). The choice of surgical method did not affect post-surgery blood chemistry in the surviving fetuses, except that the higher blood glucose in the LA fetuses at surgery tended to be maintained also post-operatively (2.0±0.2 mM versus 1.5±0.1 mM, P=0.07). The observed differences in blood chemistry parameters between the two methods of surgery and possibly in the fetal death may be explained by differences in catheterization method and the associated differences in physical and metabolic stress during and after surgery. Thus, surgery upon a standing cow in local anesthesia should be considered as an alternative to surgery in universal anesthesia for fetal catheterization in the cow in late gestation.     

Liquid storage of Asian elephant (Elephas maximus) sperm at 4 degrees C

The Asian elephant (Elephas maximus) population in the wild has been in decline for several decades and breeding in captivity has not been self-sustaining. The use of artificial insemination (AI) can help overcome many of the difficulties associated with breeding elephants in captivity; however, the ability to store semen for extended periods of time is critical to the successful application of AI to elephants. The objective of the present study was to assess the effects of four different semen extenders and the presence of egg yolk on the viability and motility of Asian elephant semen stored at 4 °C. High quality ejaculates (n=4) were collected from two Asian elephant bulls by rectal massage. Aliquots of each ejaculate were extended in four different diluents (Beltsville thawing solution (BTS); Tris–citric acid (TCA)/fructose-based; Beltsville F5 (BF5); dextrose-supplemented phosphate-buffered saline (PBS)) with or without egg yolk then cooled and stored at 4 °C. The percentages of viable (viability) and motile (motility) sperm were evaluated at 8, 24 and 48 h following collection. The addition of egg yolk significantly reduced the percentage loss in viability from initial collection to 48 h compared to extenders without egg yolk (17.0±8.2 versus 32.6±8.9 decline in percent viable sperm in the population, respectively; P<0.05). Extender and egg yolk affected (P<0.005) total motility and percent progressively motile sperm at all evaluation times during incubation. TCA + egg yolk maintained higher (P<0.05) levels of progressive motility compared to other extenders supplemented with egg yolk. These results indicate that Asian elephant semen extended in TCA diluent supplemented with egg yolk can maintain at least 50% viability and motility when stored at 4 °C for 48 h.     

Comparative aspects of the thermal biology of the short-tailed gerbil, Desmodillus auricularis, and the bushveld gerbil, Tatera leucogaster

1. 1. The response of oxygen consumption (VO₂), thermal conductance (C_d and C_min, body temperature (T_b), and evaporative water loss (EWL) of Tatera leucogaster and Desmodillus auricularis were measured over the range of ambient temperatures (T_a) from 5–35°C.

2. 2. Basal metabolic rate (BMR) of T. leucogaster was 0.841 ± 0.049 ml O₂ g⁻¹ h⁻¹ and lower than predicted, while that of D. auricularis was similar to the expected value (1.220 ± 0.058 ml O₂ g⁻¹ h⁻¹). D. auricularis had a high, narrow thermoneutral zone (TNZ) typical of nocturnal, xerophilic, burrowing rodents.

3. 3. D. auricularis and T. leucogaster regulated T_b over the range T_a = 5–35°C and kept EWL and dry thermal conductance at a minimum below the TNZ. However, the EWL of T. leucogaster increased rapidly above T_a = 30°C.

4. 4. After comparison with data from other species, it was concluded that there is an optimum size for xeric, nocturnal, burrowing rodents.

Exercise in the heat: Effects of dinitrophenol administration

1. 1.|Dinitrophenol (DNP) was administered to rats in two equal dosages (20 mg/kg, 30 min interval); the second injection was followed immediately by exercise (9.14 m/min) in the heat (30°C) or at room temperature (21°C).

2. 2.|At 21°C control (saline-treated) rats manifested a mean endurance of 94 min which was reduced to 32 min among DNP-treated animals.

3. 3.|At 30°C, control rats ran for 65 min (δT_re/min = 0.05°C) while DNP-treated animals had a mean endurance of only 12 min (δT_re/min = 0.22°C).

4. 4.|DNP-treated rats (30°C) manifested no decrements in tail-skin heat loss (δT_sk/min = 0.17°C vs 0.10°C) or saliva secretion (0.78 g/min, DNP vs. 0.19 g/min, control) for their brief treadmill duration.

5. 5.|The increased metabolic heat production of DNP severely reduced performance.

Ovarian follicular wave synchronization and pregnancy rate after fixed-time natural mating in llamas

The study was designed to compare the efficacy of treatments intended to induce follicular wave synchronization among llamas (Experiment 1), and to determine the effect of these treatments on pregnancy rates after fixed-time natural mating (Experiment 2). In Experiment 1, llamas were treated with: (1) saline (control, n=20); (2) estradiol and progesterone (E/P, n=20); (3) LH (LH, n=20); or (4) transvaginal ultrasound-guided follicle ablation (FA, n=20). The ovarian response was monitored daily by transrectal ultrasonography. The intervals from treatment to follicular wave emergence and to the day on which the new dominant follicle reached ≥7 mm, respectively, did not differ between the LH (2.1±0.3 days and 5.2±0.5 days, respectively) and FA groups (2.3±0.3 days and 5.0±0.5 days), but both were shorter (P<0.05) and less variable (P<0.01) than in the control group (5.5±1.0 days and 8.4±2.0 days), while the E/P group (4.5±0.8 days and 7.7±0.5 days) was intermediate. In Experiment 2, llamas at unknown stages of follicular development were assigned randomly to control, E/P, and LH groups (n=30 per group). A single, fixed-time natural mating was permitted 10–12 days after treatment. Ovulation rates did not differ among groups (control, 93%; E/P, 90%; LH, 90%; P=0.99), but the pregnancy rate was higher (P<0.05) for synchronized llamas (LH and E/P groups combined, 41/54) than for non-synchronized llamas (control group, 15/28). In conclusion, LH and FA treatments were most effective for inducing follicular wave synchronization, while E/P treatment was intermediate. Synchronization treatments did not influence ovulation rate subsequent to fixed-time natural mating, but a higher pregnancy rate in synchronized than non-synchronized llamas warrants critical evaluation of the effects of follicular status on the developmental competence of the contained oocyte.     

Metabolism and thermoregulation in Maximowiczi's voles (Microtus maximowiczii) and Djungarian hamsters (Phodopus campbelli)

1 Metabolic rates (Vo₂), body temperature (T_b), and thermal conductance (C) were first determined in newly captured Maximowiczi's voles (Microtus maximowiczii) and Djungarian hamsters (Phodopus campbelli) from the Inner Mongolian grasslands at a temperature range from 5 to 35 °C.

2 The thermal neutral zone (TNZ) was between 25 and 32.5 °C for Maximowiczi's voles and between 25 and 30 °C for Djungarian hamsters. Mean T_b was 37.0±0.1 °C for voles and 36.2±0.1 °C for hamsters. Minimum thermal conductance was 0.172±0.004 ml O₂/g h °C for voles and 0.148±0.003 ml O₂/g h °C for hamsters.

3 The mean resting metabolic rate within TNZ was 2.21±0.05 ml O₂/g h in voles and 2.01±0.07 ml O₂/g h in hamsters. Nonshivering thermogenesis was 5.36±0.30 ml O₂/g h for voles and 6.30±0.18 ml O₂/g h for hamsters.

4 All these thermal physiological properties are adaptive for each species and are shaped by both macroenvironmental and microenvironmental conditions, food habits, phylogeny and other factors.