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PubMed1996

Thermoregulatory vasoconstriction does not impede core warming during cutaneous heating.

BACKGROUND: Although forced-air warming rapidly increases intraoperative core temperatures, it is reportedly ineffective postoperatively. A major difference between these two periods is that arteriovenous shunts are usually dilated during surgery, whereas vasoconstriction is uniform in hypothermic postoperative patients. Vasoconstriction may decrease efficacy of warming because its major physiologic purposes are to reduce cutaneous heat transfer and restrict heat transfer between the two thermal compartments. Accordingly, we tested the hypothesis that thermoregulatory vasoconstriction decreases cutaneous transfer of applied heat and restricts peripheral-to-core flow of heat, thereby delaying and reducing the increase in core temperature. METHODS: Eight healthy male volunteers anesthetized with propofol and isoflurane were studied. Volunteers were allowed to cool passively until core temperature reached 33 degrees C. On one randomly assigned day, the isoflurane concentration was reduced, to provoke thermoregulatory arteriovenous shunt vasoconstriction; on the other study day, a sufficient amount of isoflurane was administered to prevent vasoconstriction. On each day, forced-air warming was then applied for 2 h. Peripheral (arm and leg) tissue heat contents were determined from 19 intramuscular needle thermocouples, 10 skin temperatures, and "deep" foot temperature. Core (trunk and head) heat content was determined from core temperature, assuming a uniform compartmental distribution. Time-dependent changes in peripheral and core tissue heat contents were evaluated using linear regression. Differences between the vasoconstriction and vasodilation study days, and between the peripheral and core compartments, were evaluated using two-tailed, paired t tests. Data are presented as means +/-SD; P < 0.01 was considered statistically significant. RESULTS: Cutaneous heat transfer was similar during vasoconstriction and vasodilation. Forced-air warming increased peripheral tissue heat content comparably when the volunteers were vasodilated and vasoconstricted: 48 +/- 7 versus 53 +/- 10 kcal/h. Core compartment tissue heat content increased similarly when the volunteers were vasodilated and vasoconstricted: 51 +/- 8 versus 44 +/- 11 kcal/h. Combining the two study days, the increase in peripheral and core heat contents did not differ significantly: 51 +/- 8 versus 48 +/- 10 kcal/h, respectively. Core temperature increased at essentially the same rate when the volunteers remained vasodilated (1.3 degrees C/h) as when they were vasoconstricted (1.2 degrees C/h). CONCLUSIONS: The authors failed to confirm their hypothesis that thermoregulatory vasoconstriction decreases cutaneous transfer of applied heat and restricts peripheral-to-core flow of heat in anesthetized subjects. The reported difference between intraoperative and postoperative rewarming efficacy may result from nonthermoregulatory anesthetic-induced vasodilation.

Adult↗
PubMed1998

Tissue heat content and distribution during and after cardiopulmonary bypass at 31 degrees C and 27 degrees C.

BACKGROUND: Afterdrop following cardiopulmonary bypass results from redistribution of body heat to inadequately warmed peripheral tissues. However, the distribution of heat between the thermal compartments and the extent to which core-to-peripheral redistribution contributes to post-bypass hypothermia remains unknown. METHODS: Patients were cooled during cardiopulmonary bypass to nasopharyngeal temperatures near 31 degrees C (n=8) or 27 degrees C (n=8) and subsequently rewarmed by the bypass heat exchanger to approximately 37.5 degrees C. A nasopharyngeal probe evaluated core (trunk and head) temperature and heat content. Peripheral compartment (arm and leg) temperature and heat content were estimated using fourth-order regressions and integration over volume from 19 intramuscular needle thermocouples, 10 skin temperatures, and "deep" foot temperature. RESULTS: In the 31 degrees C group, the average peripheral tissue temperature decreased to 31.9+/-1.4 degrees C (means+/-SD) and subsequently increased to 34+/-1.4 degrees C at the end of bypass. The core-to-peripheral tissue temperature gradient was 3.5+/-1.8 degrees C at the end of rewarming, and the afterdrop was 1.5+/-0.4 degrees C. Total body heat content decreased 231+/-93 kcal. During pump rewarming, the peripheral heat content increased to 7+/-27 kcal below precooling values, whereas the core heat content increased to 94+/-33 kcal above precooling values. Body heat content at the end of rewarming was thus 87+/-42 kcal more than at the onset of cooling. In the 27 degrees C group, the average peripheral tissue temperature decreased to a minimum of 29.8 +/-1.7 degrees C and subsequently increased to 32.8+/-2.1 degrees C at the end of bypass. The core-to-peripheral tissue temperature gradient was 4.6+/-1.9 degrees C at the end of rewarming, and the afterdrop was 2.3+/-0.9 degrees C. Total body heat content decreased 419+/-49 kcal. During pump rewarming, core heat content increased to 66+/-23 kcal above precooling values, whereas peripheral heat content remained 70+/-42 kcal below precooling values. Body heat content at the end of rewarming was thus 4+/-52 kcal less than at the onset of cooling. CONCLUSIONS: Peripheral tissues failed to fully rewarm by the end of bypass in the patients in the 27 degrees C group, and the afterdrop was 2.3+/-0.9 degrees C. Peripheral tissues rewarmed better in the patients in the 31 degrees C group, and the afterdrop was only 1.5+/-0.4 degrees C.

Adult↗
PubMed2006

Impact of high temperatures on mortality: is there an added heat wave effect?

BACKGROUND: Mortality during sustained periods of hot weather is generally regarded as being in excess of what would be predicted from smooth temperature-mortality gradients estimated using standard time-series regression models. However, the evidence for an effect of continuous days of exceptional heat ("heat wave effect") is indirect. In addition, because some interventions may be triggered only during forecasted heat waves, it would be helpful to know what fraction of all heat-related deaths falls during these specific periods and what fraction occurs throughout the remainder of the summer. METHODS: Extended time-series data sets of daily mortality counts in 3 major European cities (London, 28 years of data; Budapest, 31 years; Milan, 18 years) were examined in relation to hot weather using a generalized estimating equations approach. We modeled temperature and specific heat wave terms using a variety of specifications. RESULTS: With a linear effect of same-day temperature above an identified threshold, an additional "heat wave" effect of 5.5% was observed in London (95% confidence interval = 2.2 to 8.9), 9.3% in Budapest (5.8 to 13.0), and 15.2% in Milan (5.7 to 22.5). Heat wave effects were reduced slightly when we relaxed the linear assumption and these effects were reduced substantially when temperature was modeled as an average value of lags 0 to 2 days. In London, fewer than half of all heat-related deaths could be attributed to identified heat wave periods. In Milan and Budapest, the fraction was less than one fifth. CONCLUSIONS: Heat wave effects were apparent in simple time-series models but were reduced in multilag nonlinear models and small when compared with the overall summertime mortality burden of heat. Reduction of the overall heat burden requires preventive measures in addition to those that target warnings and responses uniquely to heat waves.

Epidemiologic Methods↗
PubMed2004

When defense pathways collide. The response of Arabidopsis to a combination of drought and heat stress.

Within their natural habitat, plants are subjected to a combination of abiotic conditions that include stresses such as drought and heat. Drought and heat stress have been extensively studied; however, little is known about how their combination impacts plants. The response of Arabidopsis plants to a combination of drought and heat stress was found to be distinct from that of plants subjected to drought or heat stress. Transcriptome analysis of Arabidopsis plants subjected to a combination of drought and heat stress revealed a new pattern of defense response in plants that includes a partial combination of two multigene defense pathways (i.e. drought and heat stress), as well as 454 transcripts that are specifically expressed in plants during a combination of drought and heat stress. Metabolic profiling of plants subjected to drought, heat stress, or a combination of drought and heat stress revealed that plants subject to a combination of drought and heat stress accumulated sucrose and other sugars such as maltose and glucose. In contrast, Pro that accumulated in plants subjected to drought did not accumulate in plants during a combination of drought and heat stress. Heat stress was found to ameliorate the toxicity of Pro to cells, suggesting that during a combination of drought and heat stress sucrose replaces Pro in plants as the major osmoprotectant. Our results highlight the plasticity of the plant genome and demonstrate its ability to respond to complex environmental conditions that occur in the field.

Acclimatization↗
PubMed1983

Free messenger ribonucleoprotein complexes of chicken primary muscle cells following modification of protein synthesis by heat-shock treatment.

When primary cultures of chicken myoblasts were subjected to incubation at a temperature higher than their normal growing temperature of 36-37 degrees C, the pattern of protein synthesis was altered. This condition of heat shock induced a vigorous production of a number of proteins collectively known as 'heat-shock proteins'. The synthesis of heat-shock proteins was achieved without a significant decrease in the production of a broad spectrum of proteins by muscle cells. The synthesis of three major heat-shock polypeptides with Mr values of 81 000, 65 000 and 25 000 was observed in both mononucleated dividing myoblast cells and terminally differentiated myotubes. Two-dimensional electrophoretic separation of the heat-induced polypeptides synthesized by myogenetic cultures further established that same set of polypeptides with Mr of 65 000 (pI 6.0 and 5.5), 81 000 (pI 6.2) and 25 000 (pI 5.6 and 5.3) were produced in myoblasts and myotubes. The effect of the changes in pattern of protein synthesis on the mRNA and protein moieties of non-polysomal cytoplasmic mRNA-protein complexes (free mRNP) was examined. Free mRNP complexes sedimenting at 20-35 S were isolated from the post-ribosomal supernatant of both normal and heat-shocked myotube cultures by centrifugation in a sucrose gradient. A 10-20S RNA fraction isolated from these complexes stimulated protein synthesis in a cell-free system. The RNA fraction obtained from heat-shocked cells appeared to direct the synthesis of all three major heat-shock proteins. In contrast, synthesis of these polypeptides was not detected when RNA from free mRNP complexes of normal cells was used for translation. The free mRNP complexes of both normal and heat-shocked cells showed a buoyant density of 1.195 g/cm3 in metrizamide gradients. A large number of polypeptides of Mr = 35 000-105 000 were present in the highly purified free mRNP complexes isolated from the metrizamide gradient. Similar sets of polypeptides were found in these complexes from both normal and heat-shocked myotube culture. However, the relative proportion of a 65 000-Mr polypeptide was dramatically increased in the free mRNP complexes of heat-shocked cells. Two-dimensional gel electrophoretic analysis revealed that this polypeptide and the 65 000-Mr heat-shock polypeptide exhibit similar electrophoretic migration properties. These observations suggest that, following heat-shock treatment of chicken myotube cultures, the changes in the pattern of protein synthesis is accompanied by alteration of the mRNA and protein composition of free mRNP complexes.

Animals↗
PubMed2002

Heat sterilization of peritoneal dialysis solutions influences ingestive behavior in non-uremic rats.

BACKGROUND: The appetite inhibitory effect of glucose-based peritoneal dialysis (PD) solutions may be due to glucose as such, or the hyperosmolality of the PD solution, or an effect of glucose degradation products (GDPs) formed in the PD solution during heat sterilization. This was studied in an experimental appetite model in rat. METHODS: The effect of different experimental PD solutions on ingestive behavior was investigated in non-uremic rats equipped with an implanted intraoral (i.o.) cannula through which a 1 mol/L sucrose solution was infused during tests. The amount of intake was recorded at 30 min after rats were infused intraperitoneally (IP) with 30 mL of different solutions. This method allowed an accurate and reproducible analysis of i.o. intake. The experimental PD solutions tested included (1) glucose based PD solutions with different glucose concentrations, sterilized by heat or microbiological filter, (2) glucose- and mannitol-based PD solutions with the same osmolality, sterilized by heat or microbiological filter; and (3) glucose based PD solutions, using different pH values (pH 3.0, pH 5.5 or pH 7.4) during heat sterilization. RESULTS: Following IP infusion of solutions, (1) the i.o. intake was significantly inhibited by glucose based, heat sterilized PD solutions and the degree of appetite suppression was related to the concentration of dialysate glucose in a dose-dependent way; (2) the i.o. intake was significantly less suppressed by filter sterilized than by heat sterilized glucose-based solutions; (3) the i.o. intake was significantly less following the IP infusion of glucose-based than following the mannitol-based heat sterilized solutions; however, i.o. intake did not differ between the glucose-based and mannitol-based filter sterilized solutions; and (4) furthermore, the degree of suppression of i.o. intake induced by glucose-based PD solutions was influenced by the pH value during heat sterilization. The lower the pH of the PD solution during heat sterilization, the higher the i.o. intake. CONCLUSIONS: The IP infusion of glucose-based heat-sterilized PD solutions inhibited food intake in this experimental appetite model, and the degree of suppression depended on the concentration of dialysate glucose and the pH of the solution during heat sterilization. The results suggest that GDPs formed during heat sterilization may exert a more adverse effect than glucose itself on ingestive behavior, and that a reduction of the concentration of GDPs in the PD solution using filter sterilization or a low pH value in the PD solution during heat sterilization may improve food intake.

Animals↗
PubMed1997

Telemetry augments the validity of the rat as a model for heat acclimation.

Repeated exposure to heat stress results in physiological adaptations which increase tolerance to heat stress. Core temperature (Tc) and heart rate (HR), two indices of successful heat acclimation, are both increased by the handling and restraint usually required to measure these variables in the rat. This study compares measurement of these variables in telemetry- and nontelemetry-equipped heat-acclimated rats. Four groups of male Sprague-Dawley rats were used: CAC (24, control for acclimated), HAC (24, heat acclimated), TCAC (3, telemetry implanted control for acclimation), and THAC (3, telemetry implanted, heat acclimated). The CAC and TCAC rats were maintained at 26 degrees C for 2 weeks; HAC and THAC groups were maintained at 32-33 degrees C for 2 weeks. The telemetry rats were surgically implanted with transmitters which measured activity, temperature, blood pressure (BP), and ECG. Following acclimation, the rats were subjected to a heat-stress test as follows: animals were placed in a chamber maintained at 41.5 degrees C until a Tc of 41.5 degrees C was reached, when the animals were removed to a 26 degrees C chamber to recover. The Tc of the CAC and HAC rats was manually measured with a rectal probe every 15 min. The TCAC and THAC rats had Tc, HR, and BP monitored electronically every 2.5 min from 30 min prior to heat stress through 30 min after heat. The THAC rats maintained lower Tc, HR, and BP than the TCAC rats throughout the heat stress. The CAC and HAC rats had higher Tc and slower rates of cooling after heat than either of the telemetry groups. Simultaneous measurement of HR, BP, and Tc has not previously been reported in unrestrained heat-acclimated rats. Measurement of these variables without the confounding effects of restraint or handling has increased the validity of the rat as a model for human heat acclimation.

Animals↗
PubMed1967

Recovery patterns of spores of putrefactive anaerobe 3679 in various subculture media after heat treatment.

A comparative study was made of the heat resistance of spores of putrefactive anaerobe 3679 grown in two different sporulation media and of the recovery pattern of these spores in several subculturing media after treatment with moist and dry heat. The heat resistance of the spores was characterized in the form of D and z values. The D values were determined by the modified Schmidt method. The z values were established by the graphic method. The results revealed significant differences in D and z values, depending on the type of heat and sporulation and subculture media. Spores grown in beef heart infusion showed higher heat resistance than those grown in Trypticase. Among the seven subculture media used, the largest number of spores was recovered in beef infusion. The magnitude of the D values at 121.1 C obtained with spores heated in moist heat decreased, depending on the subculture medium used, in the following order: beef infusion, pea infusion, yeast extract, liver infusion, Eugonbroth, Trypticase, synthetic medium. With spores subjected to dry heat, D values at 148.9 C decreased with the subculture medium in the following order: beef infusion, yeast extract, pea infusion and liver infusion, Trypticase, Eugonbroth, synthetic medium. The z values obtained with spores subjected to dry heat were approximately double those obtained with moist heat. Their relative magnitude varied slightly, depending on the type of subculture medium used. However, the relative magnitudes of the D values and z values with reference to the subculture media used were different with moist heat from those obtained with dry heat. Two theories are discussed as possible explanations for the logarithmic order of death of bacterial spores. The results obtained in these experiments, together with the findings of other workers, are most compatible with the theory that heat treatment of spores results in an increased rate of random injury to the genetic material of the spores.

Bacteria↗
PubMed2001

Enhanced responses of spinal dorsal horn neurons to heat and cold stimuli following mild freeze injury to the skin.

The effects of a mild freeze injury to the skin on responses of nociceptive dorsal horn neurons to cold and heat stimuli were examined in anesthetized rats. Electrophysiological recordings were obtained from 72 nociceptive spinal neurons located in the superficial and deep dorsal horn. All neurons had receptive fields (RFs) on the glabrous skin of the hindpaw, and neurons were functionally divided into wide dynamic range (WDR) and high-threshold (HT) neurons. Forty-four neurons (61%) were classified as WDR and responded to both innocuous and noxious mechanical stimuli (mean mechanical threshold of 12.8 +/- 1.6 mN). Twenty-eight neurons (39%) were classified as HT and were excited only by noxious mechanical stimuli (mean mechanical threshold of 154.2 +/- 18.3 mN). Neurons were characterized for their sensitivity heat (35 to 51 degrees C) and cold (28 to -12 degrees C) stimuli applied to their RF. Among WDR neurons, 86% were excited by both noxious heat and cold stimuli, while 14% responded only to heat. For HT neurons, 61% responded to heat and cold stimuli, 32% responded only to noxious heat, and 7% responded only to noxious cold. Effects of a mild freeze injury (-15 degrees C applied to the RF for 20 s) on responses to heat and cold stimuli were examined in 30 WDR and 22 HT neurons. Skin freezing was verified as an abrupt increase in skin temperature at the site of injury due to the exothermic reaction associated with crystallization. Freezing produced a decrease in response thresholds to heat and cold stimuli in most WDR and HT neurons. WDR and HT neurons exhibited a mean decrease in response threshold for cold of 9.0 +/- 1.3 degrees C and 10.0 +/- 1.6 degrees C, respectively. Mean response thresholds for heat decreased 4.0 +/- 0.4 degrees C and 4.3 +/- 1.3 degrees C in WDR and HT neurons, respectively. In addition, responses to suprathreshold cold and heat stimuli increased. WDR and HT neurons exhibited an 89% and a 192% increase in response across all cold stimuli, and a 93 and 92% increase in responses evoked across all heat stimuli, respectively. Our results demonstrate that many spinal neurons encode intensity of noxious cold as well as noxious heat over a broad range of stimulus temperatures. Enhanced responses of WDR and HT neurons to cold and heat stimuli after a mild freeze injury is likely to contribute to thermal hyperalgesia following a similar freeze injury in humans.

Action Potentials↗
PubMed1990

Effects of ethanol extraction and duration of heat treatment of soybean flakes on the utilization of soybean protein by growing rats and pigs.

Three experiments were conducted to determine the effects of ethanol extraction and duration of heat treatment of soybean flakes on the utilization of soybean protein by growing rats and pigs. In the first experiment, the treatments were no extraction or extraction with a 55% ethanol-water mixture (v/v), and heat treatments of 0, 5, 10, 20 and 40 min in an autoclave. Ethanol extraction improved rate (P less than .002) and efficiency of gain (P less than .001) of rats. As heat treatment was increased from 0 to 20 min, rate of gain increased, but it decreased again as heating time was increased from 20 to 40 min (P less than .03). In Exp. 2 and 3, 45 pigs were used in a growth assay and 54 were used in a N balance experiment to determine the effects of ethanol extraction on under-, intermediate- and over-processed soybean flakes (i.e., 5, 20 and 60 min of autoclaving). The heat treatments were applied either without, before or after extraction with ethanol. Responses in rate and efficiency of gain to ethanol extraction were greater for soybean flakes heated for either 5 or 60 min than for the soybean flakes heated for 20 min. When pooled across heat treatment, pigs fed the soybean flakes heated before or after extraction with ethanol gained faster (P less than .001), had greater gain:feed (P less than .001) and lower plasma urea concentrations (P less than .002) than pigs fed soybean flakes heated without extraction. Feeding soybean flakes heated and extracted with ethanol also resulted in greater apparent N retention (P less than .003), apparent N digestibility (P less than .001) and apparent biological value (P less than .03) than soybean flakes that were heated without extraction. Ethanol extraction improved the protein quality of soybean flakes, especially when the flakes were under- or overprocessed with heat.

Animals↗
PubMed2006

Heat treatment of bovine colostrum. I: effects of temperature on viscosity and immunoglobulin G level.

The objective of this study was to identify the critical temperature, at or below which heat-treatment of bovine colostrum would produce no significant changes in viscosity, IgG concentration, or Ig activity. Results of preliminary work, using a Rapid Visco Analyzer (RVA) to heat 50-mL aliquots from 6 unique batches of bovine colostrum at 59, 60, 61, 62, and 63 degrees C, suggested that colostrum could be heated to 60 degrees C for up to 120 min without changing viscosity or IgG concentration. This finding was confirmed by heating 50-mL aliquots from 30 unique batches of colostrum in an RVA for 120 min at 60 and 63 degrees C. Heating colostrum to 63 degrees C resulted in an estimated 34% decrease in IgG concentration and 33% increase in viscosity. However, there was no difference in IgG concentration between preheat-treated (73.4 +/- 26.5 mg/mL) and post-heat-treated (74.5 +/- 24.3 mg/mL) samples after heating colostrum to 60 degrees C in an RVA for 120 min. Similarly, viscosity was unaffected after heating colostrum to 60 degrees C in an RVA for 120 min. High quality colostrum (> or =73.0 mg/mL) suffered greater losses of IgG and greater viscosity changes when heated to 63 degrees C than did moderate quality colostrum (<73.0 mg/mL). However, the effects of colostrum quality were minor if high quality colostrum was only heated to 60 degrees C. The results of a bovine viral diarrhea serum neutralization assay suggested that antibody activity was unchanged after heating colostrum to either 60 or 63 degrees C. However, these results were interpreted as being inconclusive due to a high proportion of missing results because of the congealing of many samples after heat treatment. The results of this study indicate that 50-mL volumes of bovine colostrum can be heat treated at 60 degrees C for up to 120 min in an RVA without affecting IgG concentration or viscosity.

Animals↗
PubMed1998

Heat resistance of Salmonella weltevreden in low-moisture environments.

The heat resistance of Salmonella weltevreden inoculated into flour and heated in hot air was determined for (a) an initial water activity (aw) range of 0.20 to 0.60 prior to heating, (b) a range of storage relative humidities of 6.0 to 35.5% prior to heating, and (c) temperatures of 57 to 77 degrees C. The death curves obtained were biphasic, demonstrating an initial rapid decline in the numbers of survivors (1.0- to 1.5-log reductions) during the first 5 to 10 min of heating for all the temperature-water activity combinations tested. Following this initial rapid decline in the number of cells, a linear survivor curve was obtained where inactivation occurred at a slower rate. The initial decline in survivors coincided with a rapid decrease in the water activity of all the samples tested. Irrespective of the initial water activity level in the samples prior to heating, the aw decreased to < 0.2 during the first 5 to 10 min of heating. The D values obtained for these experimental parameters ranged from a D60-62 of 875 min at an initial aw of 0.4 to a D63-65 of 29 min at an initial aw of 0.5. The results demonstrated that, for any temperature, as the initial water activity of the sample prior to heating decreased, the heat resistance of the cells increased. The z values obtained from these data ranged from 15.2 to 53.9 degrees C. The relative humidity during storage prior to heating did not appear to have a significant effect on the heat resistance of S. weltevreden in flour. These results demonstrate that the amount of available water in foods that are considered to be "dry" (i.e., with a water activity less than 0.60) will significantly influence the effectiveness of the heat processing of foods and, in addition to the temperature, the aw prior to heating is a critical controlling factor during these processes.

Food Microbiology↗
PubMed1975

[A.I. in pigs: breeding efficiency of one and two inseminations per heat (author's transl.)].

Breeding efficiency as expressed by the 30-60 days non-return percentage by one and two inseminations per heat was compared. Sows and gilts in a good heat (heat detection by stockmen) received only one insemination per heat, whereas females with a moderate/weal heat received two inseminations with an interval of approx. 24 hours, provided they were still in heat at the 2nd visit. The results have been set out in the tables I and II. A total of 89.1 and 90.8 percent non-returns by one and two inseminations per heat have been obtained (table I). The difference of 1.7 percentage units in favour of two inseminations is significant, (P less than 0.001). A variation within technicians of percentage of one insemination per heat from 10-97 was found, table II. 11 technicians had significant better results with two inseminations, one technician with one insemination, and by the rest of technicians no significant differences were found between one and two inseminations per heat. It is concluded that: 1) By effective heat detection, the breeding efficiency which can be obtained by one insemination per heat, is only two percentage lower than the breeding efficiency obtained by two inseminations per heat. 2) This loss in breeding efficiency is probably compensated by the economical advantage of one insemination per heat.

Animals↗
PubMed1990

Time-temperature relationships for L1A2 cells step-down heated from 38 to 45 degrees C in vitro.

The in vitro response of L1A2 cells to a single exposure to one temperature and to step-down heating was investigated. Single heating consisted of heating for a specified time at a constant temperature in the range 38.0-45.0 degrees C, whereas step-down heating involved a pretreatment of either 45.0 degrees C for 10 min or 42.0 degrees C for 90 min. The pretreatments were adjusted to give the same survival level. The survival curves for single heating had an initial shoulder followed by an exponential region, whereas for step-down heating they were strictly exponential and had no shoulder. The time-temperature relationship for cells exposed to single heating showed a biphasic Arrhenius curve with a downward inflection at 40.5 degrees C. Biphasic Arrhenius curves were also observed for step-down heating, but both the 45 degrees C/10 min and the 42 degrees C/90 min pretreatment showed an upward inflection that broke at 42.5 degrees C and 40.5 degrees C, respectively. The downward inflection on the Arrhenius curve for single heating has been attributed to thermotolerance development and the effect of step-down heating to a temporary inhibition of thermotolerance development. However, the present shape of the Arrhenius curves for step-down heating cannot be explained by inhibition of thermotolerance. It is therefore reasonable to assume that step-down heating is more than just the inhibition of thermotolerance, and that step-down heating and thermotolerance are distinct phenomena which act independently.

Animals↗
PubMed1990

Heat-sensitive state of mouse mammary carcinoma cells in tumors.

The heat response of the SCK mammary carcinoma of A/J mice was studied in vivo and in vitro. Solid tumors or tumor cells in culture were heated in a water bath and cell survival was determined by clonogenicity in vitro. Cells in tumors were much more sensitive to heat than cells in culture. To eliminate vascular effects, tumors were dissociated into small fragments and the tumor fragments were heated in vitro, so that cells were heated while in contact with neighbors and in a complete medium. Cells in tumor fragments were as sensitive to heat as cells in tumors, even though vascular effects during heat exposure were excluded. The heat-sensitive tumor fragments gradually became heat resistant during 3 h of incubation in a complete medium at physiological temperature. The transition from a heat-sensitive to a heat-resistant state was not correlated with the development of thermotolerance or stress-related proteins. The transition was inhibited when the extracellular environment was made acidic or hypoxic but not when it was glucose and serum deprived. These results suggest that SCK tumor cells in vivo are sensitive to heat, and the heat-sensitive state appears to be established under the influence of the intratumor environment.

Adaptation, Physiological↗
PubMed1989

Heat flux from the head surface in healthy newborns and in newborns with cerebral pathology.

Scalp heat flux of fetuses during labor was shown to be related to metabolic and circulatory factors. We therefore investigated whether heat flux from the head of newborns was also related to cerebral pathology. Heat flux from the head was measured in three groups: Group A consisted of 7 newborn infants with micro- and/or hydrocephalus and with cerebral asphyxia, who were considered to have decreased heat flux from the head due to decreased heat production. Group B consisted of 3 newborn infants with hypoplastic left heart syndrome, who were considered to have increased heat flux from the head due to low cerebral blood flow and, thus, decreased heat convection from the brain. Group C consisted of 17 randomly selected healthy neonates, who served as controls. Heat flux from the head was measured by heat flux transducers attached to the skin of the forehead. The effective operative temperature in the incubator was measured with thermistors. The heat flux from the head of neonates with micro-and/or hydrocephalus and of neonates with cerebral asphyxia was distinctly below, the heat flux from the head of the neonates with hypoplastic left heart syndrome were above two standard deviations of the mean of the heat flux of healthy neonates. The results suggest that heat flux from the head is related to the metabolic or circulatory condition of the underlying brain.

Asphyxia Neonatorum↗
PubMed1987

Effects of acute and prolonged exposure to heat on regional blood flows in pregnant sheep.

This study deals with fetal growth retardation in heat-exposed sheep, and provides information on mechanisms of acclimation to heat. Radioactive microspheres were used to measure regional capillary blood flows in conscious sheep 80-100 days pregnant, at first in a thermoneutral environment, next after 2.5-6 h exposure to a hot environment of 40 degrees C, 25 mmHg water vapour pressure, and then 7 days and 15-20 days later, after spending 9 h daily in the heat. Maternal blood flow in the placental cotyledons was decreased by the first heat exposure, and remained depressed during the period of periodic heating. Reduction in placental blood flow on the maternal side could be part of the mechanism by which fetal development is retarded in heat-stressed sheep. Acclimation to heat was indicated by a decrease in the rate of rise in rectal temperature during the first 2 h of daily exposure to heat. Concomitantly, there was a progressive increase in the blood flow in extremity skin and nasal mucosa, which are tissues concerned with facilitation of heat loss during acute heat stress. However, in respiratory muscles which are also concerned with heat-loss, there was no further increase in flow after the initial response to to acute heat, indicating that heat acclimation is not due to an increased ability to pant. Blood flow in other tissues such as gut, pancreas and adipose tissue progressively decreased. These changes in blood flow have possible adaptive significance.

Acclimatization↗
PubMed1980

Appearance of heat shock proteins during the induction of multiple flagella in Naegleria gruberi.

A heat shock to amebae of the amebo-flagellate Naegleria gruberi during differentiation into swimming flagellates results in the induction of heat shock proteins as well as multiple flagella. The principal heat shock proteins migrate on sodium dodecyl sulfate-polyacrylamide gels with apparent molecular weights of 96,000, 77,000, 70,000, and 68,000. These proteins are synthesized preferentially when cells at 25 degrees C are shifted to temperatures above 32 degrees C. The maximal incorporation of methionine into heat shock proteins occurs at 38.2 degrees C, the temperature at which maximal induction of multiple flagella has been reported. Synthesis of heat shock proteins requires new transcription as judged by the ability of actinomycin D to inhibit their synthesis during the first 15 min of heat shock but not thereafter. Although heat shock can induce multiple flagella only when applied during a restricted interval, heat shock proteins are induced at any time cells are shifted to 38.2 degrees C. The response to heat shock of the Naegleria heat shock proteins resembles that of Drosophila heat shock proteins, but the two groups of proteins differ in both size and number. Naegleria heat shock proteins are, however, strikingly similar in size to a group of heat-induced proteins found in chick embryo fibroblast, mouse L, and BHK cells.

Amoeba↗