Heat tolerance in rats following administration of streptozotocin,glucose, insulin and glucose plus insulin

Rise in rectal temperature (T_re) and survival time was determined on exposure to 38°C in adult normoglycemic and diabetic (streptozotocin treated) rats and 1 h following glucose feeding or insulin administration or both, and in young rats with and without glucose feeding or insulin treatment. The heat tolerance of adult animals treated with streptozotocin and insulin plus glucose and of adult and young animals treated with glucose feeding or insulin was less than that of their respective normoglycemic controls. The rectal temperature on exposure to heat in the treated animals was significantly higher than that of controls in the adult, but not in young rats. Exposure to heat of the normoglycemic and glucose-fed animals resulted in a rise in blood glucose in the adults and a fall in the young. The already raised blood glucose level in the streptozotocin-treated animals rose further on exposure to heat. The rate of recovery of the blood glucose was not significantly altered by exposure of the animals to heat 60 min after administration of insulin or insulin plus glucose.     

The effects of acclimation to alternating environmental temperature on metabolic and endocrine responses in guinea pigs,during acute heat and cold exposure

Male Guinea pigs (n=80) were divided into four groups and maintained in a climatic chamber for three weeks in one of the following environmental conditions: (1) T_a20°C and 55% RH; (2) T_a35°C and 30–35% RH from 08:00 to 20:00 h and 5°C; 60–65% RH, from 20:00 h to 08:00 h; (3) T_a5°C and 60–65% RH; (4) T_a35°C and 30–35% RH. At the end of this period the animals were exposed to either –5°C, 60–65% RH or 45°C, 30–35% RH, for a period of 20 min, following which T_re, plasma 11-OHCS, thyroxin, glucose, and FFA, and body and organ weights were determined. The cold-warm adapted animals seemed to develop a more efficient adaptability to acute heat and cold exposure. It is suggested that on acute exposure to severe environmental conditions the endocrine and the nervous system play a dominant role in maintaining optimal body temperature, while on chronic exposure the metabolic rate of the various organs becomes relatively more important.     

The influence of exposure to cold on the incidence of gastric ulcers after reserpine in rats

Groups of female rats (n=20) exposed from 0 to 13 days to T_a's from 8.0° to 29.0°C were given 2.5 mg/kg reserpine i.p.; T_re and gastric ulcers (GU) were recorded 24 h afterwards. At exposure temperatures below 21.0°C there was a highly significant positive correlation between T_a and T_re (r=0.85) and a negative correlation between T_a and GU (r=–0.92). The GU rate after reserpine was not affected by temperatures above 21°C up to 29°C. Below 16.5°C a difference of the reserpine response was found between rats with less and more than 3 days acclimation to a given T_a. In rats with less than 3 days acclimation the mean T_re after reserpine was 1.0°C lower and the mean GU rate was 1.7 ulcers/rat higher than in rats with more than 3 days acclimation. The correlation of T_re with GU rate revealed that the mean number of GU increased with decreasing T_re · T_re and GU were negatively correlated in both series of experiments: r= –0.92 for non-acclimated rats and r= –0.95 for >3d acclimated rats. Cold acclimation of rats for 8 days at 13.0 °C or 13 days at 10.0 °C did not significantly affect T_re and the GU rate if the rats were taken to 21.0°C after reserpine administration. The results show that with and without cold-acclimation the extent of hypothermia in rats after a standard reserpine dose depends on the prevailing ambient temperature below the comfort range and the GU rate depends on the extent of the hypothermia.     

Wirkungen höher Umgebungstemperaturen auf den Wasser—und Elektrolythaushalt des Schweines in verschiedenen Wachstumsstadien

Zusammenfassung Schweine in vier verschiedenen Alters- bzw. Gewichtsstadien (20–25 kg, 40–45 kg, 60–65 kg und 90–95 kg) wurden vergleichsweise 16° bis 23°C und in der Klimakammer bei 35°C und 70–90 RF ausgesetzt. Bei erhöhter T_a stieg die Rektaltemperatur (T_re) und gleichzeitig trat in allen 4 Gruppen eine Erhöhung der Atemfrequenz, eine geringgradige Zunahme der Plasmaosmolarität, sowie eine Hyperkalämie und Hyponatriämie ein. Stieg die T_re über 40.5°C setzt eine starke Speichelsekretion ein. Die Harnosmolarität nahm bis zu einer Rektaltemperatur von 40.5°C zu, um dann wieder abzusinken. Die Na⁺-Konzentration im Harn sank mit der Erhöhung der T_re ab, während die K⁺-Konzentration anstieg.

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The effect of heat (T_a = 35°C, 70–90% rh) respiratory rate, rectal temperature (T_re), plasma and urine osmolarity, and of [Na⁺] and [K⁺] in plasma and urine in four different age/weight groups of pigs were investigated. At thermal neutral temperatures the measured physiological functions remained constant over 3 hours. At 35°C and 70–90% rh rectal temperature rose gradually. At the same time, there was a rise in respiratory rate, a slight increase in plasma osmolarity and a rise in plasma [K⁺] but a fall in plasma [Na⁺] in all four groups. The animals salivated profusely as soon as a rectal temperature of 40.5°C was reached. The urine osmolarity rose from normal to a maximum at a rectal temperature of 40.5°C and thereafter decreased. The urine [Na⁺] fell with increasing rectal temperature whereas the urine [K⁺] increased.

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Resume Des porcs de 4 classes d'âge ou plus exactement de 4 groupes de poids (20 à 25 kg, 40 à 45 kg, 60 à 65 kg et 90 à 95 kg) ont été placés soit à des températures neutres de 16 à 23°C, soit en chambre climatisée par 35°C et 70 à 90% d'humidité relative. Par température neutre, les fonctions physiologiques restent constantes durant 3 heures au moins. Par température élevée, la température rectale (T_re) se relève et, parallèlement, on constante dans les 4 groupes une augmentation de la fréquence de respiration, une faible augmentation de la pression osmotique du plasma ainsi qu'une hausse des ions [ K⁺ ], mais une diminution des ions [Na⁺] du même plasma. Les animaux ont commencé à saliver abondament dès que T_re a atteint 40,5°C. La pression osmotique de l'urine a augmenté régulièrement de la normale jusqu'à un maximum atteint lorsque T_re est arrivé à 40,5°C. Elle a diminué ensuite même si T_re dépassait ce seuil. La concentration du sodium diminue avec la hausse de T_re alors que celui du potasse augmente. On discute enfin le rôle que jouent les paramètres mesurés dans la régulation de la température et du bilan de l'eau.

     

The effects of warming by active and passive means on the subsequent responses to cold water immersion

Two experiments were undertaken to investigate the effects of warming the body upon the responses during a subsequent cold water immersion (CWI). In both experiments the subjects, wearing swimming costumes, undertook two 45-min CWIs in water at 15° C. In experiment 1, 12 subjects exercised on a cycle ergometer until their rectal temperatures (T _re) rose by an average of 0.73°C. They were then immediately immersed in the cold water. Before their other CWI they rested seated on a cycle ergometer (control condition). In experiment 2, 16 different subjects were immersed in a hot bath (40° C) until their T _re rose by an average of 0.9° C; they were then immediately immersed in the cold water. Before their other CWI they were immersed in thermoneutral water (35° C; control condition). Heart rate in both experiments and respiratory frequency in experiment 1 were significantly (P < 0.05) higher during the first 30 s of CWI following active warming. In experiment 1, the rate of fall of T _re during the final 15 min of CWI was significantly (P < 0.01) faster when CWI followed active warming (2.46° C · h^–1) compared with the control condition (1.68°C · h^–1). However, this rate was observed when absolute T _re was still above that seen in the control CWIs. It is possible, therefore, that if longer CWIs had been undertaken, the two temperature curves may have converged and thereafter fallen at similar rates; this was the case with the aural temperature (T _au) seen in experiment 1 and the T _au and T _re in experiment 2. It is concluded that pre-warming is neither beneficial nor detrimental to survival prospects during a subsequent CWI.     

Freeze or dehydrate: only two options for the survival of subzero temperatures in the arctic enchytraeid<Emphasis Type="Italic"> Fridericia ratzeli</Emphasis>

Hygrophilic soil animals, like enchytraeids, overwintering in frozen soil are unlikely to base their cold tolerance on supercooling of body fluids. It seems more likely that they will either freeze due to inoculative freezing, or dehydrate and adjust their body fluid melting point to ambient temperature as has been shown for earthworm cocoons and Collembola. In the present study we tested this hypothesis by exposing field-collected adult Fridericia ratzeli from Disko, West Greenland, to freezing temperatures under various moisture regimes. When cooled at –1 °C min^–1 under dry conditions F. ratzeli had a mean temperature of crystallisation (T_c) of –5.8 °C. However, when exposed to temperatures above standard T_c for 22 h, at –4 °C, most individuals (90%, n= 30) remained unfrozen. Slow cooling from –1 °C to –6 °C in vials where the air was in equilibrium with the vapour pressure of ice resulted in freezing in about 65% of the individuals. These individuals maintained a normal body water content of 2.7–3.0 mg mg^–1 dry weight and had body fluid melting points of about –0.5 °C with little or no change due to freezing. About 35% of the individuals dehydrated drastically to below 1.1 mg mg^–1 dry weight at –6 °C, and consequently had lowered their body fluid melting point to ca. –6 °C at this time. Survival was high in both frozen and dehydrated animals at –6 °C, about 60%. Approximately 25% of the animals (both frozen and dehydrated individuals) had elevated glucose concentrations, but the mean glucose concentration was not increased to any great extent in any group due to cold exposure. The desiccating potential of ice was simulated using aqueous NaCl solutions at 0 °C. Water loss and survival in this experiment were in good agreement with results from freezing experiments. The influence of soil moisture on survival and tendency to dehydrate was also evaluated. However, soil moisture ranging between 0.74 g g^–1 and 1.15 g g^–1 dry soil did not result in any significant differences in survival or frequency of dehydrated animals even though the apparent wetness and structure of the soil was clearly different in these moisture contents.Abbreviations DW dry weight - FW fresh weight - MP melting point - RH relative humidity - Tc crystallisation temperatures - WC water contentCommunicated by I.D. Hume     

Daily cycles of hibernation in the kangaroo rat, Dipodomys merriami

Thirty-six kangaroo rats were captured in the Mojave Desert near Las Vegas. Eight rats, group A, were kept at room temperature, 25 ± 2 °C. Ten, Group B, were kept at 13–15 °C and fed ad libitum. Eighteen, group C, were kept at 13–15 °C and fed only 2 g of dry oats daily. Rate of O₂ consumption, VO₂, food intake, rectal temperature, T_re., body weight and composition were measured in all groups. Group B showed a significant increase in VO₂, and food intake and no change in T_re body weight as compared to group A. After 2 days on the limited food intake group C began to lose weight, and T_re then began to fluctuate ranging between 14 and 36 °C; the animals exhibited hibernation when the T_re was low. Eight of the 18 rats of group C reached T_re values of 14 °C or below; only one of these survived. The lowest T_re in the other 10 was 15 °C; all survived. Chemical analysis of the homogenized rats showed a significant decrease in body fat in group C to average 1.0% contrasted with 7.8% in group B and 3.7% in group A. The VO₂ ranged from 1.9 ml/g hr at a T_re of 36.5 to 0.2 ml/g hr at a T_re of 15 °C. In conclusion D. merriami utilizes hibernation as an effective adaptive mechanism to carry out their essential body functions when on a limited food intake. It seems that maintaining a level of more than 1.5% of body fat is essential for successful arousal from hibernation.     

Vagal influence on respiratory and cardiac responses of coturnix quail to heat

Measurements of heart rate, respiratory rate, surface temperature (T_s) and rectal temperature (T_re) of mature Coturnix quail were continuously recorded for 30 min at 25° and 38°C environmental temperatures. T_s and T_re increased to a maximum level within 16 and 20 min after exposure to the 38°C environment. Thermal panting was initiated after a 1.3°C rise in rectal temperature and 12 min of exposure to 38°C. Heart rate decreased consistently during the first 20 min at 38°C, then remained at the decreased level. The increase in heart rate at 38°C following atropine injection (0.1 mg/100 g body weight) and subsequent bilateral vagotomy indicated that the decrease in heart rate is the result of an increase in vagal tone and that both efferent and afferent vagi are involved in the decreased heart rate.

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Zusammenfassung Herz- und Atemfrequenz, Oberflächen- und Rektaltemperatur erwachsener Wachteln wurden bei 25° und 38°C Raumtemperatur fortlaufend während 30 Min gemessen. T_s und T_re stiegen bei 38°C innerhalb 16–20 Min zu einem maximalen Wert an. Hecheln wurde nach 1,3°C Anstieg der T_re, 12 Min nach Exponierung bei 38°C gemessen. Die Herzfrequenz fiel gleichmässig während der ersten 20 Min bei 38°C und blieb auf diesem Niveau während der weiteren Expositionszeit. Der Anstieg der Herzfrequenz nach Injektion von Atropinsulfat (0,1 mg/100 g Kp.Gew.) und nachfolgender bilateraler Vagotomie zeigte, dass der Abfall der Herzfrequenz Folge eines erhöhten Vagotonus ist, und dass sowohl die afferenten als auch die efferenten Ä ste des Vagus beteiligt sind.

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Resume On a enregistré de façon continue durant 30 min la fréquence des pulsations et de la respiration ainsi que les températures cutanée (T_S) et rectale (T_re) de cailles adultes maintenues à des températures ambiantes de 25° et de 38°C. Les deux températures (T_s et T_re) augmentent durant 16 à 20 min après que les volailles aient été mises à 38°C, pour atteindre alors leur maximum. Les oiseaux commencent à haleter après que T_re ait augmenté de 1, 3°C, soit 12 min après le début de l'exposition à 38°C. La fréquence des pulsations diminue régulièrement durant les 20 premières minutes de l'exposition à 38°C et se maintient constante par la suite. La hausse de la fréquence des pulsations à 38°C consécutive à l'injection de sulfate d'atropine (0, 1 mg pour 100 g de poids du corps), suivie de vagotomie bilatérale, montre que la diminution observée de la dite fréquence est le résultat d'une augmentation du vagotonus et que les deux branches (afférente et efférente) du nerf vague y participant.

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Scientific Paper No. 3454. College of Agriculture, Washington State University, Pullman. Project 1915.This investigation was supported in part by funds for medical and biological research by State of Washington Initiative Measure No. 171 and the Graduate School Research Funds.     

Adaptations to terrestrial overwintering of hatchling northern map turtles,<Emphasis Type="Italic"> Graptemys geographica</Emphasis>

We conducted a 3-year field and laboratory study of winter biology in hatchlings of the northern map turtle (Graptemys geographica). At our study area in northern Indiana, hatchlings routinely overwintered in their natal nests, emerging after the weather warmed in spring. Winter survival was excellent despite the fact that hatchlings were exposed frequently to subfreezing temperatures (to –5.4 °C). In the laboratory, cold-acclimated hatchlings exhibited low rates of evaporative water loss (mean=2.0 mg g^–1 day^–1), which would enable them to conserve body water during winter. Laboratory-reared hatchlings were intolerant of freezing at –2.5 °C for 24 h, conditions that are readily survived by freeze-tolerant species of turtles. Winter survival of hatchling G. geographica probably depended on their extensive capacity for supercooling (to –14.8 °C) and their well-developed resistance to inoculative freezing, which may occur when hatchlings contact ice and ice-nucleating agents present in nesting soil. Supercooled hatchlings survived a brief exposure to –8 °C. Others, held at –6 °C for 5 days, maintained ATP concentrations at control levels, although they did accumulate lactate and glucose, probably in response to tissue hypoxia. Therefore, anoxia tolerance, as evidenced by the viability of hatchlings exposed to N₂ gas for 8 days, may promote survival during exposure to subfreezing temperatures.Abbreviations EWL evaporative water loss - FP_eq equilibrium freezing point - INA ice-nucleating agents - T_c temperature of crystallizationCommunicated by L.C.-H. Wang     

Temperature-dependent survival of isolates ofThiobacillus ferrooxidans

Psychrotrophic and mesophilic isolates ofThiobacillus ferrooxidans were examined for their ability to survive at temperatures above the T_max, below the T_min, and at –15°C after a slow freeze. There were no thermoduric strains among those studied; the viable counts decreased by two to five orders of magnitude in 24 h, following exposure to a supermaximum temperature (2–4°C above the T_max). Strain F1, when exposed to progressively higher temperatures, predictably showed increasingly rapid rates of death. When strain S2 was exposed to 2°C, a temperature below its T_min but still above freezing, there was little change in the viable counts over the 38-day observation period. When the various strains were subjected to a slow freeze at –15°C, the cells died quite rapidly with the percentage survival among the strains varying from .0006% to .0155% after 24 h. A survival curve for strain A1 showed that the number of viable cells decreased by approximately three orders of magnitude in the first 4–6 h, and a further three orders of magnitude over the next 40 h.     

Sauna-induced acceleration in insulin absorption from subcutaneous injection site.

The effect of the Finnish sauna on insulin absorption from a subcutaneous injection site was examined in eight insulin-dependent diabetic patients by measuring externally the disappearance rate of 125I-labelled rapid-acting insulin. The sauna (twice for 25 minutes at 85 degrees C) accelerated insulin absorption by 110% as compared with room temperature (p < 0.01). After the sauna blood glucose concentrations were 3.0-3.3 mmol/1 (54.1-59.5 mg/100 ml) lower than on the control day (p < 0.05). The fall in blood glucose values was proportional to the increased rate of insulin absorption (r = 0.30; p < 0.01). The hypoglycaemic effect of a sauna in insulin-treated diabetics is clearly at least partly due to enhanced insulin absorption from the injection site. Such an effect might be prevented by taking a snack or reducing the insulin dose.     

Temperature regulation in a burrow-nesting tropical seabird,the Wedge-tailed Shearwater (Puffinus pacificus)

Summary At low air temperatures (2.3–13.9°C), Wedge-tailed Shearwaters (Puffinus pacificus) shivered and their oxygen consumption increased to as much as 283% of the mean value (0.77 ml O₂/g·h) within the thermoneutral zone of air temperature (23–34°C). The minimal thermal conductance of the tissues and plumage was similar to the value predicted from the body mass (320.5 g). The oxygen consumption of the birds within their thermoneutral zone was lower than predictions based on body mass. At elevated air temperatures, the shearwaters panted at respiratory frequencies as high as 260 respirations/min; maximal respiratory frequencies were not invoked until the birds had become hyperthermic. During exposure to a hot environment, the oxygen consumption of the birds increased and in most instances the shearwaters were not able to lose heat equivalent to their concurrent metabolic heat production.Symbols and abbreviations BMR basal metabolic rate - C _total total thermal conductance - f respiratory frequency - TEWL total evaporative water loss - T _st stomach temperature - T _re rectal temperature     

Changes in the hypothalamo-pituitary-adrenocortical and hypothalamo-pituitary-thyroid axes in diabetic rats acclimated to moderate hyperthermic environment

We examined the effect of acclimation to moderate hyperthermic environment on the ACTH, TSH, T₃, T₄ and corticosterone level, as well as the relative weight of hypophysis, thyroid and adrenal glands in streptozotocin-diabetic rats. Increased activity of the hypothalamo-pituitary-adrenocortical (HPA) axis has been demonstrated in diabetic animals, whereas insulin treatment restores the changes. Heat acclimation reduces the level of ACTH and corticosterone in control animals and moderates the hormonal disturbances caused by diabetes. Simultaneously, our study revealed impairment in the activity of the hypothalamo-pituitary-thyroid (HPT) axis. Acclimation to 35±1 °C resulted in significantly lower T₃ and T₄ levels in control, diabetic and insulin-treated animals. Relative weight of the hypophysis, thyroid and adrenal glands is decreased in heat-acclimated rats. Our assumption is that there might be a cross tolerance between diabetes and heat acclimation on a hormonal level.     

Skeletal muscle pH dynamics during arousal from hibernation measured by31P NMR spectroscopy

Summary The time-course of changes in skeletal muscle pH during arousal from hibernation in the Columbian ground squirrel was studied using³¹P NMR spectroscopy. In hibernation (T _re 7–9°C), shoulder/neck muscle pH was 7.45±0.03 and _Im was 0.60. In euthermia (T _re 37°C), muscle pH was 7.24±0.05 and _Im was 0.75. Thus the overall pH-temperature coefficient was-0.009 pH units/°C, indicating acidification of the muscle in hibernation. During the transition from hibernation to euthermia, however, the muscle shows a nonlinear pattern of pH change. In early arousal (T _sh<20–25°C,T _re<15°C) muscle pH does not change and muscle _Im increases to 0.72. In later arousal (T _sh>20–25°C,T _re>15°C) muscle pH decreases gradually toward the euthermic value and muscle _Im increases only slightly from 0.72 to 0.75. These results support the hypothesis that intracellular acidification of the muscle, present during hibernation, is reversed in early arousal. This may facilitate an increase in muscle metabolism and the contribution of maximal shivering thermogenesis to rewarming of the animal.Abbreviations _Im dissociation ratio of protein imidazole buffergroups - NST non-shivering thermogenesis - BAT brown adipose tissue - dp H/dT temperature coefficient of pH - pH _i intracellular pH - ³¹ P NMR ³¹Phosphorus nuclear magnetic resonance - P _i chemical shift of inorganic phosphate relative to PCr - PCr phosphocreatine - T _b body temperature - T _re rectal temperature - T _sh subcutaneous shoulder temperature - T _a ambient temperature     

Thermoregulatory responses of Japanese Quail to various air temperatures and humidities

Measurements of rectal temperature (T_re), feather surface temperature (T_s), heart rate (HR) and breathing rate (BR) of adult Japanese Quail were taken at combinations of four mean relative humidities (rh) and stable or rising air temperature (T_a). T_re increased about 1.7° and 2.5°C at a stable T_a of 40°C from a T_a of 25°C at low (<50%) and high (> 80%) rh, respectively. T_s passively increased with T_a while remaining above T_a as high as 41°C. Panting and gular flutter rates were synchronous and approached rates of 800/min at high rh and stable T_a of 40°C. The steady-state panting rate was a direct curvilinear function of ambient water-vapor pressure (P_w). HR was depressed at successively higher, stable T_a's or with slowly increasing T_a. This thermal bradycardia may be related to the degree of discomfort or stress experienced by the animal.

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Zusammenfassung Bei Kombinationen von 4 relativen Feuchtigkeiten (rh) und konstanter oder ansteigender Temperatur (T_a) wurden Messungen der Rektaltemperatur (T_re), Federoberflächentemperatur (T_s), Herzfrequenz (HR) und Atemfrequenz (BR) an ausgewachsenen japanischen Wachteln vorgenommen. Bei T_a 40°C stieg T_re zwischen 1,7°–2,5°C an ausgehend von T_a 25°C bei <50% und > 80% rh. Die T_s folgte diesem Anstieg von T_a und überschritt ihn bis auf 41°C. Hecheln und Gurren stiegen synchron an bis auf 800/min bei hoher rh und 40°C T_a. Die erhöhte Hechelfrequenz war eine direkte lineare Funktion des Wasserdampfdruckes. HR war verlangsamt bei erhöhter, konstanter T_a. Die Hitzebradykardie steht vermutlich in enger Beziehung zu dem Ausmass der von dem Tier empfundenen Belastung.

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Resume On a soumis des cailles du Japon adultes à 4 taux différents d'humidité relative (rh) par température constante ou en hausse et mesuré la température rectale (T_re), la température superficielle des plumes (T_s), les battements du coeur (HR) et la vitesse de respiration (BR). T_re a augmenté de 1,7°C, respectivement de 2,5°C par suite d'une hausse de T_a de 25°C à 40°C par humidité basse (<50%), respectivement élevée (>80%). T_s a suivi la hausse de T_a et l'a même dépassée jusqu'à atteindre 41°C. Halètement et palpitations ont suivi la courbe de T_a pour atteindre 800/min par rh élevée et 40°C de T_a. La vitesse de respiration s'est élevée en fonction linéaire de la pression de vapeur. HR se sont ralentis par T_a élevée, mais constante. La bradycardie de chaud est probablement étroitement liée à la contrainte ressentie par l'animal.

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This investigation was supported in part by funds provided for medical and biological research by State of Washington Initiative Measure No. 171.     

Effects of temperature on the properties of primary auditory fibres of the spectacled caiman,Caiman crocodilus (L.)

Summary The effect of temperature on the response properties of primary auditory fibres in caiman was studied. The head temperature was varied over the range of 10–35 ° C while the body was kept at a standard temperature of 27 °C (T_s). The temperature effects observed on auditory afferents were fully reversible. Below 11 °C the neural firing ceased.The mean spontaneous firing rate increased nearly linearly with temperature. The slopes in different fibres ranged from 0.2–3.5 imp s^–1 °C^–1. A bimodal distribution of mean spontaneous firing rate was found (<20 imp s^–1 and >20 imp s^–1 at T_s) at all temperatures.The frequency-intensity response area of the primary fibres shifted uniformly with temperature. The characteristic frequency (CF) increased nearly linearly with temperature. The slopes in different fibres ranged from 3–90 Hz °C^–1. Expressed in octaves the CF-change varied in each fibre from about O.14oct °C^–1 at 15 °C to about 0.06 oct °C^–1 at 30 °C, irrespective of the fibre's CF at T_s. Thresholds were lowest near T_s. Below T_s the thresholds decreased on average by 2dB°C^–1, above T_s the thresholds rose rapidly with temperature. The sharpness of tuning (Q_10db) showed no major change in the temperature range tested.Comparison of these findings with those from other lower vertebrates and from mammals shows that only mammalian auditory afferents do not shift their CF with temperature, suggesting that a fundamental difference in mammalian and submammalian tuning mechanisms exists. This does not necessarily imply that there is a single unifying tuning mechanism for all mammals and another one for non-mammals.Abbreviations BF best frequency: frequency of maximal response at an intensity 10 dB above the CF-threshold - CF characteristic frequency - FTC frequency threshold curve, tuning curve - T _s standard temperature of 27 °C     

Does feeding regime affect physiologic and thermal responses during exposure to 8, 20, and 27° C?

When the loss of body heat is accelerated by exposure to low environmental temperatures, additional substrates must be oxidized to provide energy to sustain temperature homeostasis. Therefore, the present investigation examined the relation between feeding regime [pre-experimental carbohydrate feeding (FED) vs a fast (FAST)], during 120 min of exposure to 8, 20, and 27° C in well-nourished men. The following were examined: tissue insulation (I; °C · m² · W^–1), rectal temperature (T _re; °C), and oxygen consumption ( O₂; ml · kg^–1 · min^–1). O₂, T _re, and I revealed no significant differences between treatments (FED vs FAST) at any temperature. At 27° C, I was less (P < 0.05) than at 20 and 8° C, and decreased (P < 0.05) as exposure time increased. At 8° C, O₂was higher (P < 0.5) than at 20 or 27°C, and O₂increased as time increased (P < 0.05). T _re decreased (P < 0.05) as time increased for all conditions. Respiratory exchange ratio (R) differed (P < 0.05) between treatments (FED vs FAST), temperature (8 vs 20° C), and across time. Values for R suggests that carbohydrate accounted for 56% and 33% of caloric utilization during the FED vs FAST conditions, respectively. At 8 vs 20° C, R represented 54% vs 30% of cabohydrate utilization. Across time, R demonstrated that in both conditions (FED vs FAST) there was a decreased reliance on carbohydrate utilization for energy provision. From these data it appears that while substrate utilization differed between dietary treatment and across time this did not differentially affect O₂or T _re during protracted exposure to 8, 20, and 27° C. The higher R in the 8° C condition for both dietary treatments demonstrates that carbohydrate utilization is increased in shivering cold-exposed humans. However, the reduction in R across time suggests that fat oxidation is also involved in metabolic heat production and core temperature maintenance during shivering in the cold.     

Heat acclimation causes some alterations in serum enzymes activities in streptozotocin-diabetic rats

The present study investigated the effect of long-term heat acclimation and experimental diabetes on serum activity of transaminases (AST, ALT), ALP, LDH and elastase complex, as well as blood glucose and HbA1c level in Wistar rats. The heat acclimation model was established with the artificial heat chamber (35±1 °C and 30-40% humidity) for a period of 28 days, while the control groups were held on 20±2 °C. Experimental diabetes was induced by single streptozotocine (STZ) injection (55 mg/kg bodyweight) The changes caused by insulin treatment (2 IU/100 g body weight, 14 days, twice daily) in both thermal groups were also investigated.STZ-diabetes leads to significant increase in blood glucose and HbA1c level, AST, ALT and ALP activities in both thermal groups (normothermic and heat acclimated), decrease in LDH activity in normothermic animals and increase in heat-acclimated ones. Treatment with insulin restores the blood glucose, HbA1c and enzymes activities regardless of the previous thermal exposure.Prolonged acclimation of control animals to elevated ambient temperature resulted in significant decrease in blood glucose level, AST, ALT, ALP and LDH activities and non-significant changes in HbA1c. Compared to diabetic rats from room temperature, heat-acclimated diabetic ones have significantly higher blood glucose, AST, ALP and LDH activity, lower HbA1c concentration and no significant changes in ALT. Most of the changes observed in heat-acclimated insulin-treated diabetic rats did not significantly differ compared to those from room temperature.The overall two-way ANOVA analyses showed that diabetic state causes significant changes in the blood glucose, HbA1c, AST, ALT and ALP activity, while heat acclimation causes significant changes only in HbA1c level and AST activity. Both of the factors (diabetic state and heat acclimation) have significant common effects on AST, ALP and LDH activity.     

The effect of high temperatures on tissue lactate,pyruvate and venous blood properties in the rat

Brain, muscle and liver pyruvate and L(+) lactate were determined in rats (1) control, T_re=37.2°C; (2) thermal stress T_re=40.8°C; (3) terminal thermal stress T_re=43.8°C, and (4) hypoxic death at reduced oxygen tension. A second experiment was conducted to examine venous blood acid-base parameters in heated rats at imminent death. Group 2 failed to show a significant change in brain lactate concentration, but muscle lactate decreased and liver lactate increased significantly (27 and 48%, respectively). Group 3 showed significant increases of 65 and 125% in the lactate content of brain and liver, respectively, but in this instance no significance was attributed to the 12% decrease in muscle lactate. Hypoxia in Group 4 resulted in the greatest increases in tissue lactate in brain, muscle and liver (130, 50 and 171%, respectively). The pyruvate concentrations of brain and liver in Group 2 exhibited no change, but muscle pyruvate decreased significantly (59%). Group 3 brain and muscle pyruvate decreased significantly by 57 and 74%, while liver pyruvate remained unchanged. Hypoxia (4) produced no significant differences in pyruvate levels from those observed in Group 3. The changes in venous blood properties of rats heated until respiratory movement ceased suggested acute and severe metabolic acidosis while animals exhibiting heat induced spasms and loss of coordination showed only slight decreases in blood pH and bicarbonate levels. Brain water content did not change, but muscle was dehydrated and liver tissue water content increased in rats exposed to lethal temperatures. The results indicate that hypoxia probably occurs in rat tissues at high temperatures, but not to a degree that would result in death.

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Zusammenfassung Gehirn, Muskel und Leberpyruvat and 1-Laktat wurden bestimmt in Ratten (1) Kontrollen, T_re=37,2°C; (2) Hitze T_re=40,8°C; (3) tödliche Belastung T_re=43,8°C und (4) Tod durch Hypoxie bei reduziertem PO₂. In einem zweiten Experiment wurde der Säure Basengehalt des venösen Blutes in erhitzten Tieren vor Eintritt des Todes bestimmt. Gruppe 2 zeigte keine signifikante Änderung in der Gehirnlaktatkonzentration, dagegen fiel das Muskellaktat (–27%) und das Leberlaktat stieg significant(+48%). Gruppe 3 zeigte einen signifikanten Anstieg des Gehirn- (+65%) und Leberlaktats (+125%), während das Muskellaktat fiel (–11%). Hypoxie in Gruppe 4 bewirkte den grössten Anstieg des Laktats im Gehirn (+130%), Muskel (+50%) und Leber (+171%). Die Pyruvatkonzentration in Gruppe 2 zeigte nur im Muskel einen Anstieg auf +59%. In Gruppe 3 fielen das Gehirn- (–57%) und Muskelpyruvat (–74%) signifikant, ohne Änderung in der Leber. Ähnliche Resultate ergaben sich bei Hypoxie in Gruppe 4. Vor dem Eintritt des Hitzetodes war im Blut hochgradige Acidose nachweisbar, während Tiere mit Hitzespasmus und Koordinationsstörungen nur gering niedrigere pH- und Bikarbonatwerte aufwiesen. Der Gehirnwassergehalt blieb unverändert, der Muskel war dehydriert und die Leber zeigte einen höheren Wassergehalt bei letal hohen Temperaturen. Die Ergebnisse zeigen, dass Hypoxia bei Hyperthermie auftritt, doch nicht in dem Ausmasse, um zum Tod zu führen.

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Resume On a déterminé les pyruvates et lactates du cerveau, des muscles et du foie de rats présentant 4 particularités différentes: (1) T_re (température rectale) = 37,2°C (contrôle); (2) T_re = 40,8°C (contrainte de chaleur); (3) T_re = 43,8°C (contraite de chaleur limite) et (4) morts par hypoxie par suite de la réduction de la pression partielle de l'oxygène. Dans un second essai, on a déterminé le rapport acides/bases dans le sang veineux de rats sous contrainte de chaleur, juste avant leur trépas. Dans le groupe 2, on n'a pas trouvé de modification significative de la concentration des lactates du cerveau. Par contre, celle des muscles a diminué (–27%) et celle du foie a augmenté (+48%) et cela de façon significative. Dans le groupe 3, on constate une hausse du taux de lactates dans le cerveau (+65%) et dans le foie (+125%), alors que celui des muscles diminue (–11%). L'hypoxie du groupe 4 a provoqué une forte augmentation des lactates aussi bien dans le cerveau (+130%), les muscles (+50%) que le foie (+171%). La concentration des pyruvates ne fut sensiblement modifiée dans le groupe 2 que pour les muscles (+59%). Dans le groupe 3, on en note une diminution significative dans le cerveau (–57%) et dans les muscles (–74%) alors que le taux du foie reste inchangé. On a obtenu des résultats analogues par l'hypoxie dans le groupe 4. On a pu constater une acidose aigue du sang juste avant la mort de chaleur, alors que les animaux atteints de spasmes et de perturbations dans la coordination ne présentaient que peu de variations du pH et du taux de bicarbonate. Dans un état létal par hautes températures, la teneur en eau du cerveau est restée inchangée. Les muscles étaient par contre déshydratés et le foie contenait davantage d'eau. Ces résultats ont montré que, lorsque la température augmente, les animaux souffrent d'hypoxie, mais pas au point d'en mourir.

     

Cold tolerance in CCl4-treated rats and its modification by administration of garlic oil and glucose

Male Wistar rats weighing 150–200 g maintained under standard laboratory conditions and given Hindustan Lever Pellets and waterad libitum were exposed to –20°C for determination of the rate of fall of rectal temperature and survival time. The rate of fall of body temperature was significantly increased and the survival time was reduced, when animals were given an intraperitoneal injection of 1 ml/kg BW of CCl₄ 24 h but not 2 h earlier. Pre-treatment of the animals with 0.006 ml of garlic oil in a 2% solution of arachis oil for 3 days gave a significant protection to the animals against the CCl₄-induced fall in cold tolerance. Administration of glucose orally 300 mg in 2 ml of saline eliminated the CCl₄-induced fall in cold tolerance. The animals displayed a hypoglycemia 24 h, but not 2 h after injection of CCl₄. CCl₄-induced hypoglycemia was reduced by pre-treatment with garlic oil. The results indicate that the CCl₄-induced reduction in cold tolerance is secondary to hypoglycemia and not due to the direct effect of CCl₄ on the thermoregulatory mechanism in the CNS. The critical level of blood glucose below which the cold tolerance is reduced was found to be 76 mg/100 ml of blood.