Effect of warm rearing on temperature regulation in resting and exercising rats

1. 1.|Hypothalamic and rectal temperatures were recorded in 8 warm-reared (wr) and in 12 warm-acclimated control rats during resting in the heat and during 30 min running under thermoneutral conditions.

2. 2.|Brain and body temperatures of wr rats were significantly higher (P < 0.001) than control rats, both in normothermia as well as in hyperthermia; at rest, and also during exercise.

3. 3.|Warm-reared rats were more tolerant to heat.

4. 4.|During normothermia a weak selective brain cooling was present in control but absent in wr rats. During hyperthermia, however, the cooling intensified in control and occurred in wr rats.

5. 5.|The main strategy of adaptation to heat in wr rats is an upward resetting of the temperature set-point and increased passivity.

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.

Muscle temperature and muscle metabolism during short-term exercise in the goat

1. 1.|External heat exchangers acting on lower aortal blood temperature were used to dissociate hindleg muscle temperature (T_hlm) from general internal temperature (T_int) during short-term exercise of moderate intensity.

2. 2.|In series 1 39°C T_hlm was combined with 40.6°C T_int, and in series II 42°C T_hlm was combined with 39.8°C T_int.

3. 3.|At constant work rates, the 3°C difference in muscle temperature did not result in significantly different concentrations of muscle metabolites.

4. 4.|It is concluded that high local muscle temperature without general hyperthermia does not influence muscle metabolism during short-term moderate excercise.

Hyperthermia-induced changes in the morphology of CHO-K1 and their refractile inclusions

1. 1.|Chinese hamster ovary cells (CHO-K1) were heated at temperatures of 42°C and above.

2. 2.|Cells were cultured in microcapillaries to eliminate handling stress, and morphological changes were observed by light microscopy.

3. 3.|Increased incidence of membrane blebbing was noted between 1 and 2 h and few cells were viable after 2 h at 43°C.

4. 4.|Morphological changes, including the appearance of potocytotic blebs, were recorded by cinemicroscopy of microcapillary cultures on a heated microscope stage.

5. 5.|Lipid-rich refractile cell inclusions changed shape before blebbing occurred.

6. 6.|Cell retraction and rearrangement of organelles seen at 1 h at 43°C are the reverse of those seen in spreading post-trypsinized cells and suggest a thermal effect on the cytoskeleton.

Employment of a turbidimetric assay system to measure heat-induced protein aggregation

1. 1.|We developed a turbidimetric assay system for quantitation of heat-induced protein aggregation which is presumably caused by protein denaturation.

2. 2.|Rhodanese in 6 M guanidinium chloride was employed in the assay system, because this protein recognizes hydrophobic sites on denatured proteins and aggregates.

3. 3.|Turbidity caused by protein-rhodanase aggregation was recorded at 320 nm by using a u.v./VIS spectrophotometer.

4. 4.|When heated, alcohol dehydrogenase (ADH) aggregates with rhodanese. The increase of ADH-rhodanese aggregation was correlated with the loss of enzymatic activity.

5. 5.|These results indicated that the aggregation was proportional to the extent of ADH denaturation which assumingly caused the loss of ADH activity during heating at 45.5°C.

6. 6.|Similar results were observed when cytosolic proteins from CHO cells were heated at 45.5°C. Heated cytosolic proteins promoted aggregation by complex formation with rhodanese. The aggregation increased with increasing heat dose.

7. 7.|Therefore, the rhodanese assay system can be employed usefully to quantitate the protein aggregation after heat stress.

Alteration of heat sensitivity by treatment with nonpermissive temperature or cycloheximide in temperature-sensitive CHO mutant tsH1 cell

1. 1.|The temperature-sensitive mutant CHO-tsH1 and wild type (CHO-SC) cells became thermal resistant when cells were treated for either 2 h at 39.5°C before heating at 43°C or 2 h with 10 μg/ml cycloheximide (CHM) before and during heating at 43°C.

2. 2.|There was a 2000-fold increase in survival after 2.5 h at 43°C by preincubation at 39.5°C in both cell types. There was also a 200- or 700-fold increase in survival after 2.5 h at 43°C by treatment with CHM in tsH1 or SC cell type respectively.

3. 3.|In contrast to the effects at 43°C, at 41.8°C these protective effects were not evident in tsH1 cells. In wild type, however, there was an 800- or 1800-fold increase in survival after 8 h at 41.8°C by preincubation at the temperature of 39.5°C or treatment with CHM, respectively.

4. 4.|Therefore, these results suggest that killing of tsH1 at low temperature hyperthermia (41.8°C) is probably due to denaturation of thermolabile leucyl-tRNA synthetase.

5. 5.|The denaturation of this enzyme may not be protected by inhibition of protein synthesis by preincubation at the nonpermissive temperature of 39.5°C or by CHM.

The effect of hypothermia on the cardiovascular system and the pressor actions of angiotensin II

1. 1.|The effect of hypothermia (24°C) on the pressor action of angiotensin II (ANG II) was studied in anaesthetized rats.

2. 2.|Hypothermia prolonged the pressor response to ANG II leading to an increase in the estimated half-life of ANG II.

3. 3.|Hypothermia also caused a significant increase in stroke volume and a significant decrease in heart rate with no change in cardiac output.

4. 4.|It is conclued that hypothermia causes a prolongation of the pressor action of ANG II probably by reducing the activity of the catabolic enzymes leading to an increase in ANG II half-life.

Cardiovascular and thermoregulatory responses to repeated anticholinesterase administration

1. 1.|Pyridostigmine administration decreased resting heart rate by 11 ± 7 beats/min and resting oesophageal temperature by 0.23 ± 12°C after 50 h (P < 0.05). In addition, red blood cell cholinesterase activity was decreased an average of 43 ± 7% after 50 h of pyridostigmine treatment.

2. 2.|The lower heart rates and core temperatures at rest were continued during high intensity exercise in a 35°C environment. Whole body sweating was 12 ± 18% higher (P = 0.20) during exercise in the heat after 50 h of pyridostigmine treatment.

3. 3.|Repeated anticholinesterase administration had little effect on cardiovascular and thermoregulatory responses during high intensity exercise.

Hyperthermia and exercise performance in guinea-pigs (Cavia porcellus)

1. 1. Ten guinea-pigs with hypothalamic and subcutaneous interscapular thermocouples ran up to exhaustion at 1.5 km/h. Blood lactate concentrations were determined before and after exercise. Four animals exercised at constant ambient temperatures of 15 and 35°C and six other animals ran at variable ambient temperatures, adjusted to stabilize their hypothalamic temperature at 39.5, 40.5 and 41.5°C.

2. 2. Ambient temperature did not influence exercise performance directly. Duration of running was inversely proportional to hypothalamic temperature. There were no correlations between lactate concentration and exercise performance nor between lactate concentration and body temperatures.

3. 3. The results suggest a progressive decrease in exercise performance occurs with increasing body temperature.

Influence of temperature changes on the ability of gangliosides to complex with Ca

1. 1.|The influence of temperature changes on Ca²⁺-binding to brain ganglioside mixtures of different polarity, to single gangliosides (G_M1, G_D1a, G_T1b) and to their deceramide was investigated potentiometrically by means of ion-selective electrodes.

2. 2.|Following cooling (3.5°C/min.) from 37 to 13°C the Ca²⁺-binding to gangliosides, except G_M1, was increased (7–30%).

3. 3.|Subsequent rewarming from 13 to 37°C resulted in up to 100% release of previously-bound Ca²⁺.

4. 4.|When comparing the maximal absolute binding difference of Ca²⁺ to gangliosides during temperature changes a decrease of these differences could be stated which corresponds to an increase in the polarity of the gangliosides.

5. 5.|From these experiments it is concluded that a higher polarity of neuronal gangliosides is responsible for a lower thermal sensitivity of Ca²⁺-binding to these compounds. This may be involved in the process of thermal adaptation of ectothermic vertebrates.

Autonomic thermoregulatory effects of electrical stimulation of the hypothalamus in the sheep (Ovis aries)

1. 1.|The effects of electrical stimulation of the preoptic region, on autonomic thermoregulatory responses, were studied in conscious sheep at ambient temperatures of 5, 20, and 40°C.

2. 2.|Stimulation of the dorsal preoptic region elicited co-ordinated thermoregulatory responses characterized by increased respiratory frequency (RF), vasodilation of the ears and lowered body temperature. Stimulation inhibited shivering in cold environments.

3. 3.|The thermoregulatory responses were greater at 5°C in unshorn than in shorn sheep. Increased RF, induced at 20 and 40°C, persisted several minutes after stimulation ceased.

4. 4.|Intraventricular injection of noradrenaline reduced both normal and electrically-induced panting.

5. 5.|Sheep would press panels to electrically stimulate the preoptic region and this “self-stimulation” activated heat-loss mechanisms.

Effect of hyperthermia on blood constituents in the domestic rabbit (Lepus cuniculus)

1. 1. Effects of exposing rabbits to temperatures 37–50°C on body-core temperature and some blood constituents were investigated.

2. 2. Heat stroke death occurred at or above a critical core-temperature of 43.0°C.

3. 3. Plasma osmolality and levels of glucose, urea and lactate were significantly elevated in hyperthermia.

4. 4. Widespread tissue damage was indicated by increases in plasma activities of glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT) and creatinine phosphokinase (CPK).

5. 5. The most sensitive indicators of impending heat stroke in heat stressed rabbits were plasma levels or urea, lactate and CPK.

Effect of temperature on growth and bioenergetics of a tropical moth

1. 1.|Larval development and metamorphosis of Achaea junta were prolonged at 22°C, compared to 27, 32 and 35°C.

2. 2.|Overall rates of consumption, assimilation, production and metabolism of the larvae increased with temperature.

3. 3.|Efficiencies of assimilation and conversion of the digested food were significantly altered by life stage and temperature.

4. 4.|About 60% of the pupal energy was transferred to the imago at the tested temperatures.

The combined effects of ambient temperature and enforced sustained swimming activity on body temperatures of arctic charr (Salvelinus alpinus L.)

1. 1.|The difference between tissue temperatures and ambient water temperatures (ΔT) of the ectothermic Arctic charr (Salvelinus alpinus L.) ranged between 0.2 and 0.6°C.

2. 2.|For fish held at 5.7°C there were no significant differences in ΔT of exercising fish and those of controls.

3. 3.|By contrast, for fish held at 1.7°C sustained exercise led to a significant increase in ΔT of all body compartments compared with fish held in standing water (controls).

4. 4.|It is suggested that Arctic charr are capable of a limited control of metabolic heat exchange between body compartments and surrounding water when subjected to sustained exercise and ambient temperatures <2°C.

Thermosensitivity during embryonic development of Lymnaea stagnalis (Mollusca)

1. 1.|The percentage of survival after 1 hr at 40.0°C is lowest at the larval trochophore stage and at hatching of the young snail.

2. 2.|Heat resistance depends on the stage of development.

3. 3.|From the early cleavage stage onwards a higher percentage of embryos can withstand high temperature after a previous heat treatment than without it.

4. 4.|The pattern of thermosensitivity is discussed in relation to the organizational level of the stage of development.

5. 5.|It is concluded that the developing Lymnaea is a suitable system to study heat resistance and thermotolerance at the level of cells, organs and organism.

Acclimatory responses in enzymatic activity and metabolite concentrations in the tropical scorpion Heterometrus fulvipes

1. 1.|Changes in tissue metabolite concentrations and enzyme activities in the pedipalpal (PM) and heart (HM) muscles of the tropical scorpion Heterometrus fulvipes show that the metabolism in PM and HM is fundamentally reorganized following low (18°C) and high (38°C) temperature acclimation.

2. 2.|Changes in metabolite concentrations show that metabolite biosynthesis showed increases after cold acclimation but decreases after warm acclimation.

3. 3.|Similarly, changes in enzyme activities show a preponderance of glycolysis and HMP shunt activity after cold acclimation, while after warm acclimation glycogenolysis, oxidative metabolism and gluconeogenesis predominated.

4. 4.|Higher metabolite concentrations and enzyme activities both before and after thermal acclimation in HM reflect its greater compensatory abilities.

Temperature effects on evoked potentials of hippocampal slices from noncold-acclimated, cold-acclimated and hibernating hamsters

1. 1.|Neural activity was recorded in hippocampal slices from noncold-acclimated, cold-acclimated and hibernating hamsters.

2. 2.|Action potentials from a population of hippocampal pyramidal neurons were evoked by stimulating an afferent fiber tract, the Schaffer collaterals. The temperature of the artificial cerebrospinal fluid bathing the slice was varied by controlling the temperature of a water chamber jacketing the recording chamber.

3. 3.|The temperature just below that at which a population spike could be evoked, T_t, was 15.8 ± 0.9°C (mean ± SEM) for noncold-acclimated hamsters, 13.9 ± 0.3°C for cold-acclimated hamsters and 12.3 ± 0.3°C for hibernating hamsters.

4. 4.|These thresholds for evoked activity were significantly different in noncold-acclimated, cold-acclimated and hibernating hamsters, and may reflect acclimation of hippocampal neurons to cold.

Some effects of thyroidectomy on growth, heat production and the thermoregulatory ability of the immature fowl (Gallus domesticus)

1. 1.|The effect of thyroidectomy at 12 days of age on weight gain, and on heat production and thermoregulatory ability of 4- to 5-week-old chickens at temperatures within and below the thermo-neutral zone was investigated.

2. 2.|Despit the absence of thyroid tissue, as demonstrated with radioiodine, a small amount of thyroxine was found in the plasma of some thyroidectomized (TX) birds.

3. 3.|Thyroidectomy depressed weight gain; pair-fed controls grew significantly faster than TX birds.

4. 4.|Resting heat production of TX birds at thermoneutrality (30°C) was depressed by 18% (P < 0.001) and body temperature by 0.4°C (P < 0.001).

5. 5.|At 12°C heat production of TX birds was similar to that of controls but the body temperature of TX birds was 0.7°C lower (P < 0.001).

6. 6.|Thyroidectomized birds were unable to regulate body temperature at 5°C even if thyroxine was provided on the day before and at the time of cold-exposure. This inability to thermoregulate was probably due to inadequate insulation and poor nutritional status.

Effect of cycloheximide on nonpermissive temperature killing in tsH1 mutant cells

1. 1.|We investigated the mechanism of cycloheximide-induced heat protection. We proposed a hypothesis to account for the mechanism [Lee and Dewey (1986) Radiat. Res. 106, 98–110].

2. 2.|Cycloheximide protects cells from hyperthermic killing by means of protecting thermolabile proteins from denaturation.

3. 3.|For this study, we have employed temperature-sensitive mutant tsH1 which contains a thermolabile leucyl-tRNA synthetase.

4. 4.|By 15 h of incubation at the nonpermissive temperature of 39.5 or 40°C, 40 or 93% of mutant cells respectively, were killed. In contrast, wild type SC cells did not lose viability after this same incubation.

5. 5.|Although killing of tsH1 by incubation at the nonpermissive temperatures was mainly due to denaturation of a thermolabile leucyl-tRNA synthetase, cycloheximide did not protect mutant cells from killing. However, tsH1 and SC cells exhibited similar sensitivities to killing at 43°C and above. Furthermore, cycloheximide protected both cell types from hyperthermic killing.

6. 6.|There was a 200- or 700-fold increase in survival after 2.5 h at 43°C by treatment with cycloheximide in tsH1 or SC cell type, respectively. Thus, the cellular target(s) for hyperthermic killing at this temperature apparently are similar in both types of cells.

7. 7.|The data indicate that the mechanism behind cycloheximide-induced heat protection is probably not the prevention of protein denaturation.

The effect of temperature on caecal fermentation processes in a poikilothermic mammal, Heterocephalus glaber

1. 1.|The effect of temperature on caecal function was examined in the naked mole-rat Heterocephalus glaber, a poikilothermic mammal, which consumes a high proportion of fibre in its natural diet.

2. 2.|The temperature of optimal caecal function was determined from fermentation data measure at three specifically chosen temperatures (28, 33 and 40°C).

3. 3.|There was no significant difference between gas production at 33 and 40°C, however, gas production was significantly lower at 28°C.

4. 4.|The relative proportions of the gases produced were markedly different at 33 and 40°C (P ≤ 0.01). More methane and hydrogen were produced at 33°C than at 40°C.

5. 5.|These data suggest that microbial organisms within the caecum were active and functioning more effectively at 33°C (the preferred body temperature of the naked mole-rat) than at the other two temperatures.