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PubMed1991

Expression of a Conserved Family of Cytoplasmic Low Molecular Weight Heat Shock Proteins during Heat Stress and Recovery.

Plants synthesize several families of low molecular weight (LMW) heat shock proteins (HSPs) in response to elevated temperatures. We have characterized two cDNAs, HSP18.1 and HSP17.9, that encode members of the class I family of LMW HSPs from pea (Pisum sativum). In addition, we investigated the expression of these HSPs at the mRNA and protein levels during heat stress and recovery. HSP18.1 and HSP17.9 are 82.1% identical at the amino acid level and are 80.8 to 92.9% identical to class I LMW HSPs of other angiosperms. Heat stress experiments were performed using intact seedlings subjected to a gradual temperature increase and held at a maximum temperature of 30 to 42 degrees Celsius for 4 hours. HSP18.1 and HSP17.9 mRNA levels peaked at the beginning of the maximum temperature period and declined rapidly after the stress period. Antiserum against a HSP18.1 fusion protein recognized both HSP18.1 and HSP17.9 but not members of other families of LMW HSPs. The accumulation of HSP18.1-immunodetected protein was proportional to the severity of the heat stress, and the protein had a half-life of 37.7 +/- 8 hours. The long half-life of these proteins supports the hypothesis that they are involved in establishing thermotolerance.

Journal Article↗

PubMed1992

Effect of heat shock on expression of proteins not involved in the heat-shock regulon.

The effect of heat shock on the expression of some genes of Escherichia coli was tested. To avoid side effects, promoters of the genes were fused to lacZ and their expression measured by the level of beta-galactosidase. The results show that expression of umuC, recA and polB, after induction of the SOS response, was somewhat higher in the heat-shocked than in the non-shocked cells, whereas expression of ada, alkB and alkA genes, after induction of the adaptive response, was about the same. Unexpectedly, it was found that expression of lacZ from its own promoter was drastically lowered in the heat-shocked cells. This effect, however, seems not to be dependent on the induction of heat-shock proteins.

Enzyme Induction↗

PubMed1978

Bacterial contamination of heat-sterilized, heat-disinfected and chemically-disinfected haemodialysis monitors.

The bacterial contamination of one heat-sterilized, three heat-disinfected and four chemically-disinfected monitor types was evaluated before and after dialysis. All monitor types were contaminated. In the heat-treated monitors the level of contamination varied with the intensity of the heat treatment and the technical design. They were less contaminated than the chemically-disinfected recirculating single-pass monitors. The latter were contaminated to a marginal degree, irrespective of the quality of the water supply. Each monitor showed a characteristic microbial flora, indicating that recontamination occurred from the same persistent focus. Aquired antibiotic resistance characters were rare among the potential human pathogens isolated from the dialysate. The level of contamination during dialysis is determined by a complex of factors, including the mode of disinfection, the technical design of the dialysis equipment, the duration of the dialyses, and the flora of the dialysate.

Anti-Bacterial Agents↗

PubMed1981

Production of heat-labile or heat-stable enterotoxins by strains of Escherichia coli belonging to serogroups O44, O114, and O128.

Strains of Escherichia coli which belong to enteropathogenic serogroups usually fail to produce heat-labile or heat-stable enterotoxins. However, 1 of 34 strains of E. coli O44, 9 of 45 strains of E. coli O114, and 18 of 82 strains of E. coli O128 produced heat-labile or heat-stable enterotoxins. Most enterotoxigenic isolates were from tropical or developing countries; all three enterotoxigenic strains isolated in Britain were from patients returned from abroad. Enterotoxigenic strains were of many different flagellar types. Certain enterotoxigenic strains of E. coli O114 and O128 possessed colonization factor antigen I.

Antigens, Bacterial↗

PubMed1983

Immunization of swine with heat-stable Escherichia coli enterotoxin coupled to a carrier protein does not protect suckling pigs against an Escherichia coli strain that produces heat-stable enterotoxin.

Pregnant swine were immunized parenterally with purified heat-stable Escherichia coli enterotoxin that was made antigenic by coupling it to bovine immunoglobulin G. Immunized swine had high titers of antitoxin in serum and colostrum as measured by radioimmunoassay. However, the heat-stable enterotoxin neutralizing titers of the serum and colostrum from immunized swine were comparatively low. Newborn pigs suckling their immunized dams were not protected against challenge with porcine enterotoxigenic E. coli that produce heat-stable toxin but do not produce heat-labile toxin.

Animals↗

PubMed1987

Neutralizing activity of monoclonal antibodies to heat-sensitive and heat-resistant epitopes of Rickettsia rickettsii surface proteins.

Antiprotein monoclonal antibodies derived from mice inoculated with Rickettsia rickettsii heated at 56 degrees C for 15 min are of two types: one is type specific for epitopes denatured by moderate temperatures, and the other is specific for epitopes resistant to 100 degrees C for 5 min. The heat-resistant epitopes are found by immunoblotting on multiple polypeptides after solubilization of the rickettsiae at temperatures of 56 degrees C or higher. Most, but not all, antibodies to the heat-sensitive epitopes passively protected mice against two 50% lethal doses of R. rickettsii, whereas none of the antibodies to heat-resistant epitopes did.

Animals↗

PubMed1979

Protein and ribonucleic acid syntheses in heat-damaged and heat-killed Escherichia coli.

Protein and ribonucleic acid (RNA) syntheses were measured in both lethally injured and thermally damaged viable cells after heating at lethal temperatures. Immediately after heating, cells were incubated in growth media containing either [14C]leucine or [3H]uracil. The labeled cells were subsequently treated with penicillin. Viable cells were shown to lyse, and the intact nonviable cells were collected by centrifugation. The results showed that after heating, protein and RNA synthesis were reinitiated in the penicillin-sensitive cell population, but there was no detectable protein or RNA synthesis in the heat-killed cells which were resistant to penicillin. The lack of protein or RNA synthesis in lethally damaged cells during the entire recovery period may be interpreted to reflect the lethal thermal damage.

Bacterial Proteins↗

PubMed1982

Further evaluation of the Biken test (modified Elek test) for detection of enterotoxigenic Escherichia coli producing heat-labile enterotoxin and application of the test to sampling of heat-stable enterotoxin.

A total of 2,229 strains of Escherichia coli isolated from subjects with traveller's diarrhea were tested for heat-labile enterotoxin production by the Biken test (Honda et al., J. Clin. Microbiol. 13:1--5, 1981). Results of the Biken test showed a 99.0% coincidence with those obtained by Chinese hamster ovary cell assay. The use of antiserum against E. coli heat-labile enterotoxin gave sharper and clearer results than did the use of antiserum against cholera enterotoxin. Samples for heat-stable enterotoxin assay were obtained from the agar plates used for the Biken test, and the heat-stable enterotoxin activities of these samples were compared with those of samples obtained from standard liquid cultures. Results for samples of 2,229 strains from the Biken agar plates and from liquid cultures were almost identical.

Bacteriological Techniques↗

PubMed1980

The catecholamine precursor L-3,4-dihydroxyphenylalanine inhibits both heat production and heat loss mechanisms in the rabbit.

The effects of catecholamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) on the thermoregulatory responses of conscious rabbits to different ambient temperatures (Ta) (2, 22, and 30 degrees C) were assessed. Intravenous administration of L-DOPA alone, intravenous administration of L-DOPA plus R04-4602 (a peripheral decarboxylase inhibitor), and intraventricular administration of L-DOPA or norepinephrine all produced a hypothermia at Ta 2 degrees C. The hypothermia was due to a decrease in metabolic heat production (M). On the other hand, L-DOPA or norepinephrine produced both behavioral excitation and hyperthermia at both Ta 22 and 32 degrees C. At Ta 22 degrees C, the hyperthermia was due to decreased ear skin blood flow (EBF) and slightly increased M (due to behavioral excitation) whereas at Ta 32 degrees C the hyperthermia was due to EBF, decreased respiratory evaporative heat loss, and slightly increased M (due to behavioral excitation). Further, the temperature effects induced by L-DOPA were antagonized by pretreatment with 6-hydroxydopamine (a relative depletor of catecholaminergic nerve fibers) but not with haloperidol (a relative blocker of dopaminergic receptors). The data indicate that activation of central adrenergic receptors via the endogeneous release of norepinephrine with L-DOPA inhibits both heat production and heat loss mechanisms in the rabbit.

Animals↗

PubMed2005

The role of heat-conducting walls in the measurement of heat and mass transport in transient grating experiments.

We present a two-dimensional model to account for the role of heat-conducting walls in the measurement of heat transport and Soret-effect--driven mass transport in transient holographic grating experiments. Heat diffusion into the walls leads to non-exponential decay of the temperature grating. Under certain experimental conditions it can be approximated by an exponential function and assigned an apparent thermal diffusivity D(th, app)<D(th, s), where D(th,s) is the true thermal diffusivity of the sample. The ratio D(th, app)/D(th, s) depends on only three dimensionless parameters, d/l(s), kappa(s)/kappa(w), and D(th, s)/D(th, w). d is the grating period, l(s) the sample thickness, kappa(s) and kappa(w) the thermal conductivities of sample and wall, respectively, and D(th,w) the thermal diffusivity of the wall. If at least two measurements are performed at different d /l(s), both D(th,s) and kappa(s) can be determined. Instead of costly solving PDEs, D(th,s) can be obtained by finding the zero of an analytic function. For thin samples and large grating periods, heat conduction into the walls plays a predominant role and the concentration grating in binary mixtures is no longer one-dimensional. Nevertheless, the normalized heterodyne diffraction efficiency of the concentration grating remains unaffected and the true thermal and collective diffusion coefficient and the correct Soret coefficient are still obtained from a simple one-dimensional model.

Journal Article↗

PubMed1982

Thermoregulatory responses in the rat to exercise in the heat following prolonged heat exposure.

To determine the effects of prolonged exposure to severe thermal stress on the subsequent ability to exercise in the heat, rats were exposed to a hot (35 degrees C) environment for 1, 2, 3, or 4 wk. At each of these weekly intervals the rats ran on a treadmill to hyperthermic exhaustion (41.5--43.0 degrees C), and tail-skin (Tt-sk) and rectal (Tre) temperatures were monitored. The results indicated that prolonged heat exposure did not enhance the rats' endurance capacity. Further, as the period of heat stress increased, there was a concomitant significant decrement in tail-skin vasodilation; indeed, after 3 and 4 wk at 35 degrees C Tt-sk reflects a complete shutdown of blood flow to the tail during exercise. Additionally, slight evaporative cooling from exogenous fluid (saliva or urine from the treadmill surface) might account for the low Tt-sk in relation to Tre and Ta. Hematocrit ratios ordinarily decreased from week to week during heat exposure, whereas body weights remained very consistent throughout the 4-wk interval. The mechanism of this decrement in vasodilation is undergoing further study.

Adaptation, Physiological↗

PubMed1987

Effect of age on heat-activated sweat gland density and flow during exercise in dry heat.

Physiological responses of eight postmenopausal older women (age 52-62 yr) and eight younger women (age 20-30 yr) were compared during moderate intensity exercise in a hot dry environment (48 degrees C dry bulb, 25 degrees C wet bulb). The age groups were matched on the basis of maximal O2 consumption (VO2max), body surface area, and body fatness. After heat acclimation the women walked at 40% VO2max for up to 2 h in the hot dry environment while heart rate (HR), rectal temperature (Tre), mean skin temperature (Tsk), whole-body sweating rate (Msw), and local sweating rates (msw; forearm, chest, and scapula) were measured. Additionally, the density of heat-activated sweat glands (HASG) was determined and average sweat gland flow (SGF) was calculated for the scapular area. Although no differences between age groups were found in HR response (when analyzed as percent of maximal HR) or Tsk, the older women had a significantly higher Tre throughout the heat-exercise session. The greater heat storage of the older women may be explained by their significantly lower Msw and msw. There were no differences between the younger and older women in the density of HASG after 30 min; therefore, the lower msw reflects a diminished output per HASG rather than a decrease in the number of sweat glands recruited. The diminished thermoregulatory ability of the older women, unrelated to differences in VO2max, appears to reflect either 1) a diminished response of the sweat glands to central and/or peripheral stimuli, or 2) an age-related structural alteration in the eccrine glands or surrounding skin cells.

Adult↗

PubMed1990

Convective heat transfer measured directly with a heat flux sensor.

A heat flux disk has been developed that directly measures the convective heat transfer in W/m2. When the sensor is calibrated on an aluminum cylinder, the calibration constant obtained is greatest in still air. As air movement increases, the calibration constant is reduced with increasing convective heat transfer coefficient, 0.5%.W-1.m2.K. The influence of wind on the calibration value is greatly reduced when the sensor is attached to a surface with lower thermal conductivity. The local convective heat transfer coefficient (hc) of the human body was measured. The leg acts in a manner similar to that of a cylinder, with the highest hc value at the front facing the wind and the lowest approximately 90 degrees from the wind, and in the wake a value is obtained that is close to the average hc value of the leg. When hc is measured at several angles and positions all over the body, the results indicate that the body acts approximately as a cylinder with a hc value related to the wind speed as hc = 8.6.v0.6 W.m-2.K-1, where v is velocity.

Biophysical Phenomena↗

PubMed1990

Errors in heat flux measurements due to the thermal resistance of heat flux disks.

Questions have been raised regarding the effect of the thermal resistance of heat flux transducers (HFTs) on the thermal flux from the skin. A model capable of simulating a large range of "tissue" insulation (variable-R model) was used to study the effect of the underlying tissue insulation on the relative error in heat flux due to the thermal resistance of the HFTs. The data show that the deviation from the true value of heat flux increases as the insulation of the underlying tissue decreases (r = 0.99, P less than 0.001). The underestimation of the heat flux through the skin measured by an HFT is minimal when the device is used on vasoconstricted skin in cool subjects (3-13% error) but becomes important when used during vasodilation in warm subjects (29-35% error) and even more important on metallic-skin mannequins (greater than 60% error).

Body Temperature Regulation↗

PubMed1995

Mechanical ventilation with heated humidifiers or heat and moisture exchangers: effects on patient colonization and incidence of nosocomial pneumonia.

The contribution of ventilator circuit bacterial contamination to the occurrence of ventilator-associated pneumonia remains controversial. In a previous study, we found that the incidence of pneumonia was identical with ventilator circuit changes every 48 h and with no ventilator circuit changes. The present study prospectively assessed whether keeping ventilator circuits clean with a heat and moisture exchanger exhibiting antimicrobial barrier properties affects patient colonization and the incidence of nosocomial pneumonia in patients receiving mechanical ventilation for more than 48 h. Consecutive patients were randomly allocated to humidification with either a heat and moisture exchanger (Group 1, n = 61) or a heated humidifier (Group 2, n = 70). In both groups, no circuit changes were performed throughout ventilatory support. Duration of mechanical ventilation was identical in both groups (10 +/- 8.6 d (range: 2 to 47) in Group 1 and 12.5 +/- 14.2 d [range: 2 to 85] in Group 2). The incidence of pneumonia (positive quantitative culture of protected brush specimen) was similar in both groups (6/61 and 8/70 in Groups 1 and 2, respectively; p = 0.8), as was duration of ventilation prior to pneumonia (9 +/- 5.9 versus 8.2 +/- 5.7 d; p = 0.8). Ventilator tubing contamination was considerably reduced with the use of a heat and moisture exchanger. In contrast, bacterial colonization of the pharynx and trachea was identical in both groups. These results suggest that circuit colonization plays little or no role in the occurrence of ventilator-associated pneumonia, provided usual maintenance precautions are applied.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1986

Circulatory heat sources for canine respiratory heat exchange.

We assessed the roles of the pulmonary and bronchial circulations as potential heat sources to the pulmonary airways during respiratory heat loss, by observing the changes in airstream temperature that accompanied temporary occlusion of the pulmonary or bronchial circulations. Baseline end-expiratory and end-inspiratory airstream temperatures were 35.4 +/- 0.2 degrees C (SEM) and 30.9 +/- 0.3 degrees C, respectively, among all trials. With occlusion of the lower lobe pulmonary arteries for 3 min ipsilateral end-expiratory and end-inspiratory airstream temperatures fell by 2.8 +/- 0.2 and 1.1 +/- 0.2 degrees C, respectively, during hyperpnea with room temperature air, and by 3.5 +/- 0.5 and 1.8 +/- 0.2 degrees C, respectively, during hyperpnea with frigid air. In marked contrast, interruption of the bronchial circulation for 3 min had no effect on airstream temperatures. These data indicate that under these conditions, the pulmonary circulation, but not the bronchial circulation, serves as an important local heat source for respiratory heat exchange within the pulmonary airways.

Animals↗

PubMed1983

Immunocytochemical localization of fatty acid metabolizing heat-stable and heat-labile enoyl-coenzyme A (CoA) hydratases in liver and renal cortex.

Two enzymes, the heat-stable and the heat-labile enoyl-coenzyme A (CoA) hydratases, involved in the metabolism of fatty acids were localized in liver and renal cortex using specific antibodies, immunofluorescence, and the protein A-gold immunocytochemical technique. The qualitative and quantitative results have demonstrated that the heat-stable enoyl-CoA hydratase is a mitochondrial membrane-associated protein of hepatocytes and of epithelial cells in proximal and distal renal tubules. The hepatic sinusoidal cells, as well as the endothelial and epithelial cells of the glomeruli, fail to demonstrate any specific labeling. The heat-labile enoyl-CoA hydratase, on the other hand, was detected in the peroxisomal matrix of hepatocyte and proximal tubule epithelial cells. Its distribution was identical to that of catalase. The significance of the differential distribution of peroxisomal and mitochondrial enoyl-CoA hydratases is discussed in relation to their function.

Animals↗

PubMed2006

Ventilator-associated pneumonia using a heated humidifier or a heat and moisture exchanger: a randomized controlled trial [ISRCTN88724583].

INTRODUCTION: Some guidelines to prevent ventilator-associated pneumonia (VAP) do not establish a recommendation for the preferential use of either heat and moisture exchangers (HMEs) or heated humidifiers (HHs), while other guidelines clearly advocate the use of HMEs. The aim of this study was to determine the incidence of VAP associated with HHs or HMEs. METHODS: A randomized study was conducted in the intensive care unit of a university hospital involving patients expected to require mechanical ventilation for >5 days. Patients were assigned to two groups; one group received HH and the other group received HME. Tracheal aspirate samples were obtained on endotracheal intubation, then twice a week, and finally on extubation, in order to diagnose VAP. Throat swabs were taken on admission to the intensive care unit, then twice a week, and finally at discharge from the intensive care unit in order to classify VAP as primary endogenous, secondary endogenous, or exogenous. RESULTS: A total of 120 patients were assigned to HMEs (60 patients) and HHs (60 patients); 16 patients received mechanical ventilation for less than five days and were excluded from the analysis. Data analysis of the remaining 104 patients (53 HMEs and 51 HHs) showed no significant differences between groups regarding sex, age, Acute Physiology and Chronic Health Evaluation II score, pre-VAP use of antibiotics, days on mechanical ventilation, and diagnosis group. VAP was found in eight of 51 (15.69%) patients in the HH group and in 21 of 53 (39.62%) patients in the HME group (P = 0.006). The median time free of VAP was 20 days (95% confidence interval, 13.34-26.66) for the HH group and was 42 days (95% confidence interval, 35.62-48.37) for the HME group (P <0.001). Cox regression analysis showed the HME as a risk factor for VAP (hazard rate, 16.2; 95% confidence interval, 4.54-58.04; P < 0.001). CONCLUSION: The patients mechanically ventilated during more than 5 days developed a lower incidence of VAP with a heated humidifier than heat and moisture exchanger.

Adult↗