Mechanisms of heat protection by cycloheximide or puromycin: Involvement of polyamines?

1. 1.|When Chinese hamster ovary cells are treated with cycloheximide (10 μg/ml) or puromycin (100 μg/ml) for 2 h before and during heating at 43°C for 3 h, there is protection from hyperthermic killing; i.e. the plating efficiency increases 2000-fold from 3.7 × 10⁻⁵ to (6–9) × 10⁻².

2. 2.|The total intracellular levels of spermidine and spermine are not altered by the hyperthermic or drug treatments.

3. 3.|The small 30% decrease in intracellular putrescine observed after heating is not altered by drug treatment.

4. 4.|Heat protection by treatment with cycloheximide or puromycin cannot be attributed to changes in levels of total intracellular polyamines.

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.

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.

How are neuronal thermosensitivity and lack of thermoreception related in the duck's hypothalamus? A tentative answer

1. 1.|In 15 conscious Pekin ducks, 40 “warm sensitive” hypothalamic neurons were identified according to their discharge rates at 40°C T_hy (F₄₀), local temperature coefficients (Δ/ΔT) and Q₁₀.

2. 2.|Q₁₀ and either F₄₀ or ΔF/ΔT were little or not related.

3. 3.|A positive correlation between F₄₀ and ΔF/ΔT was observed which was particularly close (r = 0.94 and 0.96) when the neurons were classified according to their Q₁₀ of <2 and >2.

4. 4.|The results suggest that neurons with positive temperature coefficients in the duck's hypothalamus mostly exhibit linear to exponential temperature-discharge relationships.

5. 5.|This is an contrast to observations on mammalian hypothalamic thermosensitive neurons and may relate to the absence of the thermosensory function in the duck's rostral brainstem.

The effect of incubation temperatuer on oxygen consumption and organ growth in domestic-fowl embryos

1. 1.|Oxygen consumption and organ growth were measured in domestic-fowl embryos incubated at different temperatures (36, 38 and 40°C).

2. 2.|Embryonic oxygen consumption was highest at an incubation temperature of 40°C and lowest at 36°C. These differences were ascribed largely to variations in embryo size at different incubation temperatures.

3. 3.|At incubation temperatuers of 40 and 38°C, there was a plateau in oxygen consumption late in incubation, but this was not apparent at 36°C.

4. 4.|At 36°C, some tissues (e.g. eyeballs) were “spared” the repression of growth that characterized the embryo as a whole, while other tissues (e.g. stomach) incurred a much greater growth reduction. Similarly, at 40°C, stomach growth exceeded that of the embryo as a whole, while the eyeballs were largely spared the enhanced growth.

5. 5.|A simple index of tissue age revealed that, in general, there were consensual changes in tissue maturity and growth at different temperatures but that there were some disparities between growth and maturity in individual organs.

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.

Temperature dependence of the germination of tomato seeds

1. 1.|The germination of tomato “C38” seeds exposed to periodical white incandescent light occurs from 6.0° ± 0.2°C to 37.5° ± 0.2°C, being rate-limited for 10.3° T 25.9°C, and elsewhere limited by the germination capacity.

2. 2.|Rate averages are linearly T-dependent outside their optimum range (25.9° T 29.5°C) and rate variances are typically heterogeneous.

3. 3.|The smooth curvilinear Arrhenius plot indicates that diffusion processes cannot be rate-limiting outside the interval 25.9° T 29.5°C, whereas phase transitions and (or) transconformation of proteins may limit the rate above 34.9°C and, by opposite effects, below 15.3°C.

4. 4.|The thermal communication between the environment and the germinating seed proceeds by a temperature signal which is quenched by random thermal noise at T 11.2°C and at T 34.0°C.

Electrical skin resistance and rectal temperature changes in resting human subjects exposed to heat

1. 1.|Fourteen male volunteers were examined under passive heating.

2. 2.|Electrical skin resistance (ESR) and rectal temperature (T_re) were measured during the whole period of exposure.

3. 3.|It was found that:

• —|ESR decreases rapidly with increasing air temperature. Assuming an exponential curve yields a mean time constant of 14 min.

• —|There is a correlation between the individual ESR time constants and T_re increases (r = 0.695, P < 0.005).

• —|Additional changes of ESR were noted in 8 subjects at a constant air temperature of 42°C.

4. 4.|It is concluded that ESR may be a useful indicator of the sweating response of the human thermoregulatory system during exogenous heat load.

Heat death and cellular heat injury

1. 1.|Evidence is presented implicating cellular membranes in cellular heat injury. It is proposed this is the site of the primary lesion.

2. 2.|Secondary and tertiary events, resulting from the primary lesion, cause organism death. Those events may be unique to the life style and grade of organisation of the organism.

3. 3.|Thus hyperthermia may cause “excessive” fluidisation of membranes and so cause impairment of membrane permeability and disrupt the stability of membrane enzymes.

4. 4.|Homeoviscous adaptation of membrane fluidity may well have an important role in resistance acclimation as well as resistance adaptation.

Hatching of freshwater sponge gemmules after low temperature exposure: Ephydatia mülleri (Porifera: Spongillidae)

1. 1.|Gemmules of Ephydatia mülleri can withstand exposure to temperatures down to −80°C for 63 days without loss of hatchability.

2. 2.|Hatching is slowed following exposure to temperatures below −27°C.

3. 3.|There is a slight but significant relationship between gemmule size and the time to hatch.

4. 4.|This species can withstand long-term exposure to winter air temperatures occurring within its known geographic range.

Effect of temperature on the electrical activity of the rat epididymis in vitro

1. 1.|Regional differences in the frequency of electrical activity in rat epididymis were maintained at all temperatures below 39°C.

2. 2.|The change in frequency per deg C increased with temperature and was highest in the temperature region of 34–39°C and the Arrhenius plots of the frequency were linear and parallel in all parts of the epididymis.

3. 3.|The Q₁₀ of the frequency varied between 2.2.–4.3.

4. 4.|The conduction velocity at the cauda epididymis was highest (2.8 mm/s) at 37°C. The Q₁₀ of the conduction velocity was 2.3 in the temperature region of 24–37°C.

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.

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.

Thermohaemolysis of human erythrocytes in isotonic NaCl/sucrose media during transient heating

1. 1.|The hyperhermia induced haemolysis of cells and resealed ghosts suspended in isotonic NaCl/sucrose media was studied upon transient heating.

2. 2.|At 61.5°C a process of temperature accelerated disturbance of membrane permeability barrier was initiated, wich was sensed by the consequent volume changes. Concomitantly with this process the thermohaemolysis appeared as a threshold colloid-osmotic lysis.

3. 3.|The initial temperature of this successive barrier disturbance was decreased linearly by ethanol. At 18% ethanol this barrier disturbance took place at 39°C while spectrin was denaturated at about 45°C. Apparently, the spectrin denaturation was not sufficient, nor was involved in, the initiation of this membrane disturbance.

4. 4.|The membrane of cells made ion permeable in the presence of 18% ethanol by heating to 39°C contained irreversible pores with a radius of about 0.45 nm.

5. 5.|This suggests a conformational change of a protein(s) in their formation, but not spectrin nor the anion channel.

6. 6.|Using specific amino reagents it was ascertained, that a superficial NH₃⁺ group dissociable at neutral pH impeded this thermo-induced pore formation.

7. 7.|Consistent results show that this formation of membrane pores initiated at 61.5°C may be included in the still unknown mechanism of thermohaemolysis.

Thermal responses of the fresh water turtle Mauremys caspica to step-function changes in the ambient temperature

1. 1.|The turtle Mauremys caspica cools significantly faster than it heats in air. The heating/cooling ratio is 0.49.

2. 2.|The variation of body temperature in relation to time-course in response to a step-function change of environmental temperature, fitted to a second-order system improves that of a first-order system.

3. 3.|The gradient between ambient temperature (T_a) and equilibrium body temperature (T_b) increases significantly and progressively when ambient temperature rises over 25°C.

4. 4.|At 40°C thermoregulatory hyperventilation was detected, implying an increase in air convection requirement (ventilation relative to O₂ consumption, ).

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.

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.

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.

Variations in the activity of fatty ACYL-CoA desaturases and electron-transport components in Tetrahymena microsomes with temperature and age of culture

1. 1.|Alterations in the fatty acid composition of microsomes were most marked in the exponential phase of both 39.5- or 15°C- grown Tetrahymena pyriformis NT-1.

2. 2.|Activities of palmitoyl-CoA and stearoyl-CoA desaturases were lower in 15°C cells than in 39.5°C cells, while the activity of oleoyl-CoA desaturase was higher in 15°C cells.

3. 3.|Activities of the terminal component of the desaturation system as well as all three desaturases (palmitoyl-CoA, stearoyl-CoA, oleoyl-CoA) were higher in the exponential phase than in the stationary phase for cells grown at both temperatures.

4. 4.|NAD(P)H-cytochrome c reductase activity and cytochrome b₅ content were reduced whereas NADH-ferricyanide reductase activity was increased in the stationary phase at both 39.5 and 15°C.

Thermal sensations during simultaneous warming and cooling at theh forearm: A human psychophysical study

1. 1.The forearm of 5 female subjects ws thermally stimulated by 2 sets of interposed servo-thermodes that respectively drove skin temperature at ±0.1°C.s⁻¹ for 25 s and then held it constant. Mean skin temperature remained constant. The sequence was repeated at adapting temperatures between 22.5 and 37.5°C.

2. 2.Thermal sensations, continuously reported by the position of a dial, were warmer for heterogeneous thermal stimuli than for homogeneous stimuli when mean skin temperature was greater than 30°C and cooler when less than 27.5°C.

3. 3.This phenomenon is inconsistent with a single additive contribution of “warm” and “cold” information to thermal sensations.