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PubMed2003

Temperature course and distribution during plasma heating with a microwave device.

In spite of the much shorter thawing times, the use of microwave devices for heating units of fresh frozen plasma is still being discussed. Concerns about general and localised overheating are the main arguments against the use of microwave devices. We evaluated the warming of fresh frozen plasma using the recently introduced Transfusio-therm 2000(R) microwave blood warmer. Units of fresh frozen plasma were weighed and the heating times were recorded. The surface temperature of the fresh frozen plasma bags during heating was recorded every 10 s. Temperature variation on the surface was examined by measuring the difference between peripheral and centrally placed temperature sensors. After heating, plasma temperature was determined using a calibrated thermometer. There were no signs of overheating during the heating process. The surface temperature of three units of fresh frozen plasma heated simultaneously (n = 45) was 34.0 degrees C (SD, 1.5 degrees C) after a mean heating time of 23.2 min (SD, 1.1 min). The mean (SD) temperature difference was -0.6 (0.5) degrees C and the mean (SD) plasma temperature was 33.6 (0.8) degrees C. Heating one fresh frozen plasma unit at a time (n = 20), the mean (SD) heating time was 6.3 (0.4) min. The surface temperature after heating was 34.3 (0.2) degrees C, the mean (SD) temperature difference was -0.6 (0.4) degrees C and the mean (SD) plasma temperature after heating 33.1 (0.6) degrees C. We conclude that no general or localised overheating of fresh frozen plasma occurs during or after heating with the microwave blood warmer.

Blood Preservation↗
PubMed2001

Effects of quercetin on the heat-induced cytotoxicity of prostate cancer cells.

BACKGROUND: It has been demonstrated that prostate cancer cells are relatively sensitive to heat stress. We have reported that heat treatment at 43 degrees C increases the expression of heat shock protein 70 (hsp70) in prostate cancer cells, leading to apoptosis. Hsp70 is a protein that protects cells against heat damage. Cells with lower levels of hsp70 have been shown to have a higher sensitivity to heat stress. Therefore, downregulation of hsp70 is expected to enhance heat-induced inhibitory effects on cell growth. Quercetin has been reported to be an agent that inhibits hsp70 expression. The present study was undertaken to investigate the effects of quercetin and/or heat on the growth of prostate cancer cells in vitro. METHODS: Three human prostate cancer cell lines were used: Lncap; PC-3; and JCA-1. The cells were treated with quercetin and/or heat. Alterations in the cell cycle and hsp70 expression were examined by means of flow cytometry (FCM). The apoptotic cells were detected by FCM using fluorescein isothiocyanate (FITC) labeled annexin V. RESULTS: Treatment with quercetin alone resulted in an apparent decrease of hsp70-positive cells and an increase of subG1 cells in JCA-1 and LNcap cells. Quercetin inhibited an increase of hsp70 expression after heat treatment and increased the number of subG1 cells with lower levels of hsp70 in JCA-1 and LNcap cells. Quercetin was found to enhance heat-induced inhibitory effects on cell growth and heat-induced apoptosis in both JCA-1 and LNcap cells. CONCLUSION: These results suggest that quercetin may enhance heat-induced cytotoxicity in prostate cancer cell lines through the inhibition of hsp70 production.

Apoptosis↗
PubMed1984

Developmental control of the heat shock response in Xenopus.

Xenopus cells express two major proteins on heat shock, designated hsp 70 and hsp 30. Several cDNA clones for the corresponding mRNAs were identified and sequenced. Inducibility and abundance of heat shock mRNAs in various cell types and developmental stages was determined by nuclease S1-mapping. The only cells found to contain hsp 70 mRNA without heat shock are the oocytes. The level of this stored hsp 70 mRNA is not increased by heat shock. After fertilization, hsp 70 mRNA becomes undetectable; it appears as a heat-inducible mRNA for the first time at gastrulation. After this stage, all somatic cell types accumulate hsp 70 mRNA to similar levels on heat shock, presumably by transcriptional activation of the hsp 70 genes. In contrast, hsp 30 mRNA is not detectable, even after heat shock, in oocytes or embryos that induce hsp 70 mRNA to high levels. Heat inducibility appears late in development--at the tadpole stage. However, the level of induced mRNA varies considerably in different adult tissues. This indicates that the Xenopus heat shock genes are not coordinately controlled. A long-term developmental control appears to be superimposed on the temporary heat inducibility of the heat shock genes: stage- or cell-type-specific conditions can lead to constitutive or repressed heat shock genes.

Aging↗
PubMed2003

Gap junctional intercellular communication and cellular response to heat stress.

Gap junctional intercellular communication (GJIC) is essential in the maintenance of tissue homeostasis and has been implicated in tumor suppression. Recent studies have indicated that GJIC is also involved in cellular stress responses to low dose ionizing radiation, UV light and hydrogen peroxide. However, the contribution of GJIC to the heat stress response has not yet been elucidated. We here demonstrate a potential link between GJIC and the heat stress response. First, we investigated whether the abolition of GJIC by lindane affects heat sensitivity in normal human cells. Lindane potentiated cell killing by heat shock at 43 degrees C, whereas little or no cytotoxicity was observed at 37 degrees C. Nuclear translocation of heat shock protein 72 (HSP72) was interrupted by lindane, although its induction was not affected. These results indicate that lindane exacerbates hyperthermic lethality via disrupted nuclear translocation of HSP72 protein. Second, we assessed whether heat shock alters GJIC and phosphorylation of gap junction connexin (Cx) proteins in normal human cells. Persistent heat treatment augmented Cx43 phosphorylation in a heat- and time-dependent fashion and this phosphorylation was recovered after heat shock. GJIC was also disturbed by heat shock. These results indicate that heat shock augments Cx43 phosphorylation leading to GJIC abrogation. Our present results imply that GJIC contributes to protection against heat stress and that loss of GJIC function during carcinogenesis exacerbates hyperthermic lethality.

Cell Communication↗
PubMed1993

Heat stress limits infarct size in the isolated perfused rabbit heart.

OBJECTIVE: Heat stress, with the expression of heat stress proteins, has been shown to protect the rabbit heart in vitro against global ischaemia/reperfusion injury, though no benefit is apparent in an in vivo rabbit model of infarct size. The aim of this study was therefore to investigate this discrepancy and to discover whether heating itself has any effect which could negate the protection derived from myocardial stress protein synthesis. METHODS: (1) To ascertain whether heat stress could limit infarct size in the absence of blood, isolated buffer perfused hearts, with or without prior heat stress, were subjected to 45 min of regional ischaemia and 120 min reperfusion, and the resulting infarct size was expressed as a percentage of the risk area (I/R%). (2) The observations were repeated in an isolated blood perfused heart model in which a support rabbit (heat stressed or control) was used to perfuse the isolated heart. RESULTS: In the buffer perfused heart, prior heat stress reduced I/R from 70.8(SEM 4.4)%, n = 10, in controls to 51.5(5.7)%, n = 12 (p < 0.05). In hearts perfused by support rabbits, prior heat stress reduced I/R [from 34.7(3.7)%, n = 16, to 23.5(3.3)%, n = 15 (p < 0.05)] only when the perfusing rabbit was a control (not heat stressed). If the perfusing rabbit had been heated, I/R was greater in both heat stressed and control hearts [51.9(7.0)% and 44.9(3.3)%, p < 0.05 v control support rabbit]. CONCLUSIONS: Heat stress limits infarct size in this rabbit model. However it appears to have additional adverse effects, probably on the blood, which may override any benefit associated with myocardial stress protein synthesis.

Animals↗
PubMed2006

Heat shock-induced changes in lipid and protein metabolism in the endoplasmic reticulum of barley aleurone layers.

Heat shock in barley aleurone layers induces heat shock protein synthesis and suppresses secretory protein synthesis by selectively destabilizing their mRNAs. In addition, the endoplasmic reticulum (ER) membranes upon which secretory protein mRNAs are translated become vesiculated during heat shock, leading to the hypothesis that ER dissociation and targeted mRNA destabilization are linked mechanistically. Supporting this, ER can be heat adapted, and heat-adapted ER has higher levels of fatty acid saturation in membrane phospholipids which do not vesiculate upon heat shock. Secretory protein mRNAs are also more stable in heat-adapted cells. To understand better heat shock-induced changes in ER membranes, we examined ER membrane proteins and enzymes involved in phosphatidylcholine biosynthesis and phospholipid turnover in heat-shocked aleurone cells. Heat shock significantly increased the activity of phospholipases A2 and D, and shortly thereafter significant but gradual increases in choline kinase and phosphocholine glyceride transferase activities and a sharp increase in phosphorylcholine citidyl transferase activity were observed. Only minor changes were observed in SDS-PAGE analyses of proteins from sonicated ER membranes fractionated on continuous sucrose gradients. Overall, heat shock reduced total lipid in ER membranes relative to protein, and in intact, ultracentrifuged aleurone cells examined by light and electron microscopy the ER band appeared to increase in density. The changes in phospholipid metabolism coupled with the suppression of secretory protein synthesis indicate that in addition to inducing a classic heat shock response, high temperature also induces a classic unfolded protein response in the ER of this secretory cell.

Endoplasmic Reticulum↗
PubMed1999

Osmotic regulation of the heat shock response in H4IIE rat hepatoma cells.

The influence of cell hydration on the heat shock response was investigated in H4IIE hepatoma cells at the levels of HSP70 expression, MAP kinase activation, induction of c-jun and the MAP kinase phosphatase MKP-1, heat resistance, and development of tolerance/sensitization to arsenite after a priming heat treatment. Induction of HSP70, MKP-1, and c-jun by heat was delayed, but more pronounced or sustained, under hyperosmotic conditions compared with normo- and hypo-osmotically exposed cells. Anisosmolarity per se was ineffective to induce HSP70; some expression of the mRNAs for MKP-1 and c-jun in response to hyperosmolarity was found, but was small compared with the response to heat. Heat-induced activation of JNK-1 was increased under hyperosmotic conditions and more sustained than the JNK-activity induced by hyperosmolarity at 37 degrees C. A prominent Erk-2 activation was found immediately after heat shock under hypo- and normo-osmotic conditions, but Erk-2 activation was weak in hyperosmolarity-exposed cells. Despite anisosmotic alterations of the heat shock response at the molecular level, the heat resistance of H4IIE cells toward heat shock was not affected by ambient osmolarity. However, an osmolarity-dependent sensitization to arsenite was induced by a priming heat shock. The osmodependence of the H4IIE cell response to heat differs from that recently found in primary rat hepatocytes. The data are discussed in terms of cellular adaption mechanisms and their physiological relevance.

Animals↗
PubMed2002

Heat shock protein and high-dose aspirin: effects on random skin flap survival in a rat model.

The heat shock response is known to have a protective effect against flap ischemia. It has been shown that heat shock protein (hsp) expression can be augmented in vivo with the administration of high-dose aspirin before heat treatment. The authors hypothesized that administration of aspirin before hsp induction through heat stress would enhance further the protective effects of the heat shock response against skin flap ischemia. They used a random dorsal skin flap model in 32 rats divided into four groups (N = 8 each): control, heat shock, aspirin plus heat shock, and aspirin. Before surgery, rats in the two heat shock groups were placed in a 45 degrees C water bath until core body temperature measured 42 degrees C, and they were maintained at 42 degrees C for 15 minutes. Rats in the two aspirin groups received a single oral dose of aspirin (100 mg per kilogram) 1 hour before heat bath or surgery. Immunohistochemistry confirmed hsp expression in the two heat groups. Skin flap survival was improved significantly (p < 0.05) in the heat shock (55%), aspirin plus heat shock (58%), and aspirin (60%) groups when compared with controls (45%). Contrary to their hypothesis, aspirin combined with hsp induction did not offer greater protection from ischemia than hsp induction alone (p > 0.05). However, high-dose aspirin administration alone did improve skin flap survival when compared with controls. Future studies are needed to investigate further the role of pharmacological therapy combined with hsp induction in improving skin flap survival and to delineate the dose-response relationship between aspirin and hsp.

Animals↗
PubMed2000

The effect of heat on cytokine production in rat endotoxemia.

OBJECTIVE: To determine whether heat stress protects the endotoxemic rat by up-regulation of the counterinflammatory cytokine interleukin (IL)-10, thereby attenuating the inflammatory response. DESIGN: A total of 16 rats were assigned to either the heat stress group (n = 8) or the control group (n = 8). The heat stress group was warmed to a temperature of >42 degrees C (107.6 degrees F) rectally for 10-15 mins; 20 hrs later, all rats were intubated, paralyzed, and ventilated. After jugular venous and arterial catheterization, endotoxin was given intravenously. Arterial blood was removed at 0, 2, 4, and 5 hrs for blood gases, tumor necrosis factor (TNF)-alpha, nitric oxide metabolites (NO), IL-10, and macrophage inflammatory protein (MIP)-2. The alveolar macrophages were removed, counted, and then incubated for 24 hrs. The supernatant was analyzed for TNF-alpha, NO, IL-10, and MIP-2. SETTING: University research laboratory. SUBJECTS: Male Sprague-Dawley rats (n = 16). INTERVENTIONS: Administration of heat before endotoxin infusion. MEASUREMENTS AND MAIN RESULTS: Alveolar-arterial oxygen gradient was lower in the heat stress group at 4 and 5 hrs after endotoxemia. Plasma and alveolar macrophage supernatant concentrations of TNF-alpha, NO, and IL-10 were not affected by heat. Plasma and alveolar macrophage supernatant MIP-2 concentrations were higher in endotoxemic rats receiving heat pretreatment compared with controls. CONCLUSIONS: Our study demonstrates that heat leads to pulmonary protection of short duration in severe endotoxemia. This protection was not mediated by plasma TNF-alpha, IL-10, or NO. Contrary to our hypothesis, pretreatment with heat increased rather than decreased the plasma MIP-2 concentration and alveolar macrophage production of MIP-2 in endotoxemia. The mechanism of heat-conferred pulmonary protection in endotoxemia remains unclear. Alveolar macrophages do not produce IL-10 in endotoxemia. The increased MIP-2 production by heated alveolar macrophages was not attributable to alterations in production of either TNF-alpha or IL-10. The significance of increased MIP-2 by endotoxin-exposed alveolar macrophages in heated rats is unknown.

Animals↗
PubMed2002

Heat shock preconditioning impairs revascularization of freely transplanted pancreatic islets.

BACKGROUND: Revascularization of freely transplanted pancreatic islets is essential for appropriate graft function and survival. During the first days after transplantation, however, islet transplants are avascular, and successful engraftment is believed to be markedly hampered by hypoxia-induced tissue injury. Because heat shock has been shown to induce cell resistance against hypoxia, it seems reasonable to stress pancreatic islets by heat before transplantation. In contrast, hypoxia is a major stimulus for angiogenesis, and thus heat shock preconditioning-induced resistance against hypoxia may decrease stimulation of angiogenesis. The authors therefore studied in vivo whether heat shock preconditioning of isolated islets affects angiogenesis and revascularization after free transplantation. METHODS: After collagenase isolation, heat shock-preconditioned islets (42 degrees C for 30 min) were transplanted syngeneically into nontreated skinfold chambers of Syrian hamsters. In a second group of animals, nontreated islets were transplanted into heat shock-preconditioned chambers. Nontreated islets transplanted into nontreated chambers served as controls. Islet angiogenesis and revascularization were quantitatively analyzed during 14 days after transplantation using intravital fluorescence microscopy. Expression of heat shock proteins (HSP) was confirmed by immunohistochemistry and Western blotting. RESULTS: Immunohistochemistry revealed expression of HSP32 (heme oxygenase [HO]-1), HSP72, and also intracellular insulin in isolated and transplanted pancreatic islets. Western blot analysis showed enhanced HSP32 but slightly decreased HSP72 expression in heat shock-preconditioned islets when compared with controls. Intravital microscopy revealed appropriate vascularization of control islets within 14 days after transplantation. Heat shock preconditioning of the host tissue (i.e., the skinfold chambers) did not affect islet vascularization when compared with controls. In contrast, heat shock preconditioning of the isolated islets resulted in a significantly (P < 0.05) impaired take rate, a reduced (P < 0.05) size of the newly formed microvascular network, and thus a smaller area (P < 0.05) of microvascularly perfused endocrine tissue. CONCLUSION: These data suggest that heat shock preconditioning of isolated pancreatic islets before transplantation impairs the process of graft angiogenesis and revascularization. Therefore, transient exposure of isolated islets to heat may not be considered a promising tool to improve the outcome of islet transplantation.

Animals↗
PubMed2006

Activated protein C therapy in a rat heat stroke model.

OBJECTIVE: To evaluate the therapeutic effects of activated protein C in an animal model of heat stroke. DESIGN: Laboratory investigation. SETTING: Chi-Mei Medical Center research laboratory. SUBJECTS: Male Sprague-Dawley rats weighing 252-304 g. INTERVENTIONS: Anesthetized animals were subjected to heat stress (40 degrees C) to induce heat stroke. A bolus injection of normal saline or recombinant human activated protein C (drotrecogin alfa, activated) was conducted via femoral catheters immediately after the onset of heat stroke. Blood sampling was done before initiation of heat stress and 0 and 40 mins after the onset of heat stroke. MEASUREMENTS AND MAIN RESULTS: When the vehicle-treated rats underwent heat exposure, their survival time values were found to be 56-64 mins (n = 16). Resuscitation with activated protein C significantly and dose-dependently improved survival during heat stroke (108-246 mins for doses of 0.5-20 mg of activated protein C per kilogram of body weight) (n = 32). All heat-stressed animals displayed systemic inflammation and activated coagulation, evidenced by increased tumor necrosis factor-alpha, prothrombin time, activated partial thromboplastin time, and D-dimer and decreased platelet count and protein C. Biochemical markers evidenced by cellular ischemia and injury/dysfunction included increased plasma levels of blood urea nitrogen, creatinine, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and alkaline phosphatase; increased striatal levels of glutamate, glycerol, and lactate/pyruvate ratio; and decreased striatal levels of partial pressure of oxygen and local cerebral blood flow, which were all observed during heat stroke. These heat stroke reactions were all significantly suppressed by resuscitation with activated protein C but not vehicle solution. CONCLUSIONS: The results indicate that systemic delivery of human recombinant activated protein C at the time point of onset of heat stroke may improve survival by ameliorating systemic inflammation, hypercoagulable state, and tissue ischemia and injury in multiple organs.

Alkaline Phosphatase↗
PubMed1990

Hydrogen peroxide activates immediate binding of a Drosophila factor to DNA heat-shock regulatory element in vivo and in vitro.

The synthesis of heat-shock proteins via activation of heat-shock genes occurs in response to heat and various physical or chemical stressing agents. Transcriptional activation of heat-shock genes requires a heat-shock regulatory element in their promoter, to which a heat-shock specific transcription factor binds. In Drosophila cells, the heat-shock factor already exists in unstressed cells in an inactive form and acquires the capacity to bind to the heat-shock element following stress. The mechanism of this activation is not known: neither is it known whether the different stressing agents induce the heat-shock response through a common mechanism. We previously proposed that many agents known to induce the heat-shock response (substances interfering with respiratory metabolism, agents reacting with sulphydryl groups, metals, recovery from anaerobiosis and ischemia) might act via accumulation of reactive oxygen species, i.e. superoxide ion or H2O2. We show here that H2O2, introduced either in Drosophila cell cultures or in cell extracts, was able to activate heat-shock-element binding. Activation was rapid and H2O2 concentration dependent, with a threshold of 1 microM. These results were confirmed with mouse fibroblast cells. This very rapid activation, in vivo or in vitro, suggests a direct effect of H2O2 either on the heat-shock factor itself or on its activator.

Amino Acid Sequence↗
PubMed1983

Dephosphorylation of S6 and expression of the heat shock response in Drosophila melanogaster.

A basic ribosomal phosphoprotein of 30,000 molecular weight was rapidly dephosphorylated in cultured Drosophila melanogaster cells heat shocked at 37 degrees C. The protein was associated with the 40S ribosomal subunit and had an electrophoretic mobility similar to that of purified rat liver protein S6 on basic two-dimensional polyacrylamide gels as well as a similar partial proteolysis peptide map. In logarithmically growing cultures, this D. melanogaster S6 protein appeared to have a single phosphorylated species consisting of 30 to 40% of the total cellular S6. Thus, the nearly complete dephosphorylation of this protein observed in heat shock involves a large fraction of the cellular S6. The significance of this dephosphorylation in the expression of the heat shock response was investigated by examining the phosphorylation status of S6 in recovery from heat shock and in response to chemical inducers of the heat shock response. During recovery from a 30-min heat shock, the recovery of normal protein synthesis was almost complete in 2 to 4 hr, whereas there was no significant rephosphorylation of S6 for 8 h. Two chemical inducers of the heat shock response, canavanine and sodium arsenite, induced the synthesis of heat shock proteins in D. melanogaster cells. Sodium arsenite also caused an inhibition of normal protein synthesis similar to that observed in heat shock. Neither agent, however, caused significant dephosphorylation of S6. These results suggest that the dephosphorylation of S6, although invariably observed in heat-shocked cells, may in some cases be dissociated from both the induction of heat shock protein synthesis and the turnoff of normal protein synthesis which occur in a heat shock response.

Animals↗
PubMed1988

Transcriptional activation of heat-shock genes in eukaryotes.

Prokaryotes and eukaryotes respond to thermal or various chemical stresses by the rapid induction of a group of genes collectively referred to as the heat shock genes. In eucaryotes, the expression of these genes is primarily regulated at the transcriptional level. The early observations that transfected heat shock genes were inducible in heterologous systems suggested the existence of common regulatory elements in these ubiquitous genes. Sequence analysis of cloned Drosophila heat shock genes revealed a conserved 14 base pair (bp) inverted repeat, which is essential for heat induction. This regulatory sequence, referred to as the heat shock element (HSE), is found in multiple imperfect copies upstream of the TATA box of all heat shock genes. While studies in heterologous systems indicated that a single copy of HSE was sufficient for inducibility, further analysis in homologous assays suggests that multiple HSE can act in a cooperative way and that the efficiency of transcriptional activation is related, within limits, to the number of HSE. Comparative analysis of heat shock genes reveals that HSE can be positioned at different distances from the TATA box in either orientation, a behavior reminiscent of enhancer elements. However, the presence of HSE does not necessarily confer heat inducibility, as shown by their presence in the constitutively expressed but non-heat-inducible homologous cognate genes. Footprinting and nuclease mapping have been used to show that a protein factor (HSTF: heat shock transcription factor) binds to the HSE element, activating heat shock gene transcription in a dose-dependent manner. The recent progress in the isolation and characterization of HSTF in Drosophila, yeast, and human cells is reviewed. Finally, different models suggested to account for the positive regulation of heat shock genes by the HSTF are presented.

Animals↗
PubMed2002

Heat acclimation in rats: modulation via lipid polyunsaturation.

Heat acclimation of rats has been shown to enhance endurance of rat hearts to ischemic insult and acute heat stress. Common protective features have been shown to be operative during both these stress-inducing conditions. To explore the role of membrane lipid composition in the adaptive response, we analyzed two major parameters that impact membrane dynamics and order, the nonesterified cholesterol levels and the acyl chain composition of phospholipids, in rat heart and salivary glands, both major thermoregulatory organs, in short- and long-term heat-acclimated rats. Before exposure to heat, control salivary gland tissue has a higher cholesterol-to-phospholipid mole ratio (0.32 +/- 0.02) than heart (0.14 +/- 0.01), and the acyl chains of its phospholipids are 50% more saturated. The remodeling strategies of the tissues after exposure to heat differed. Heart cholesterol levels increased after short-term heat acclimation (approximately 50%), whereas salivary gland cholesterol levels decreased in acute heat stress and long-term heat acclimation (approximately 32%). Remodeling of phospholipid acyl chains, particularly an increase in docosahexaenoic acid, was a protective strategy in both tissues (57% in heart and >100% in salivary glands). Modifying membrane lipid composition by treating rats with liposomes composed of egg phosphatidylcholine (PC) before exposure to heat resulted in a 38% increase in endurance to thermal stress. The density and affinity of muscarinic receptors of submaxillary salivary glands, involved in the acclimation response, were measured in control and PC liposome-treated rats, and then both groups were subjected to short-term heat acclimation. After PC treatment the well-established compensatory upregulation of the muscarinic receptors and concomitant decrease in their affinity was blunted. The substantial increase in the thermal endurance of heat-challenged intact rats after treatment with PC liposomes (600 vs. 200 min) suggests that membrane lipid composition plays a role in the ability of these tissues to respond to heat stress.

Adaptation, Physiological↗
PubMed2000

The thermophysiology of uncompensable heat stress. Physiological manipulations and individual characteristics.

In many athletic and occupational settings, the wearing of protective clothing in warm or hot environments creates conditions of uncompensable heat stress where the body is unable to maintain a thermal steady state. Therefore, special precautions must be taken to minimise the threat of thermal injury. Assuming that manipulations known to reduce thermoregulatory strain during compensable heat stress would be equally effective in an uncompensable heat stress environment is not valid. In this review, we discuss the impact of hydration status, aerobic fitness, endurance training, heat acclimation, gender, menstrual cycle, oral contraceptive use, body composition and circadian rhythm on heat tolerance while wearing protective clothing in hot environments. The most effective countermeasure is ensuring that the individual is adequately hydrated both before and throughout the exercise or work session. In contrast, neither short term aerobic training or heat acclimation significantly improve exercise-heat tolerance during uncompensable heat stress. While short term aerobic training is relatively ineffective, long term improvements in physical fitness appear to provide some degree of protection. Individuals with higher proportions of body fat have a lower heat tolerance because of a reduced capacity to store heat. Women not using oral contraceptives are at a thermoregulatory disadvantage during the luteal phase of the menstrual cycle. The use of oral contraceptives eliminates any differences in heat tolerance throughout the menstrual cycle but tolerance is reduced during the quasi-follicular phase compared with non-users. Diurnal variations in resting core temperature do not appear to influence tolerance to uncompensable heat stress.

Adaptation, Physiological↗
PubMed1995

Developmental changes in sensitivity of bovine embryos to heat shock and use of antioxidants as thermoprotectants.

Experiments were conducted with in vitro-produced bovine embryos to determine whether 1) increased culture temperatures (i.e., heat shock) adversely affected embryonic development, 2) embryos become more resistant to heat shock as they advance in development, and 3) selective antioxidant molecules alleviate heat shock effects on embryonic development. Development of 2-cell embryos to > or = 16-cell stage on d 5 after in vitro fertilization was not affected by a heat shock of 40 degrees C for 3 h, but 41 or 42 degrees C for 3 h decreased (P = .004) development. In a separate experiment, development of 2-cell embryos was decreased (P = .01) by exposure to 41 degrees C for 3 h but not for 1 h. In contrast, development of morulae to blastocysts was not affected by heat shock of 41 degrees C for 1 or 3 h. Medium supplementation with 50 nM glutathione or 50 mM taurine before heat shock did not reduce the effects of heat shock (41 degrees C for 3 h) on 2-cell embryos. Likewise, addition of glutathione ester, a more membrane-permeable analog of glutathione, did not protect 2-cell embryos from heat shock. In conclusion, early bovine embryos are susceptible to disruption in development caused by heat shock. As embryos progress in development, they acquire resistance to heat shock. Glutathione, taurine, and glutathione ester were not effective in alleviating the effects of heat shock on development of 2-cell embryos. Consequently, molecules have yet to be identified that can protect early-stage bovine embryos from the adverse effects of heat shock.

Animals↗
PubMedDate not supplied

Effects of hyperthermic temperatures and the synthesis of heat-shock proteins on the lateral diffusion of H-2Kk.

The effect of hyperthermia, fractionated heat and the synthesis of heat shock proteins on the lateral diffusion of H-2Kk was examined in RDM-4, Ch-1 and mouse L cells. Cells in suspension were examined immediately after heating, adaptation to growth at 40 degrees C for 72 h or 6 h after exposure to sodium arsenite (5 microM), iodoacetamide (10 microM) or a 20 min heat shock at 45 degrees C. No heat shock protein synthesis could be measured in CH-1 cells in response to either heat or chemical stress. Synthesis of these proteins was observed in both RDM-4 and mouse L cells in response to heat or chemical treatments, and the kinetics of synthesis were similar to those reported in the literature for other eukaryotic cell lines. The diffusion of fluorescein isothiocyanate-labelled monoclonal anti-H-2Kk bound to heat (or chemically) treated cells was measured by the technique of fluorescence recovery after pattern photobleaching. After a 30 min exposure to temperatures between 41 degrees C and 45 degrees C, a temperature-dependent decrease in recovery was observed. At 45 degrees C, 75-100% of the surface antigen was found to be immobile. The diffusion coefficients of the mobile fractions were not significantly changed at all the temperatures examined. Heat effects on the recovery patterns of all the three cell lines were qualitatively similar and unaffected by the presence or absence of heat or chemically induced heat shock proteins. After 48-60 h following a heat shock, the recovery patterns were similar to those of unheated control cells.

Animals↗