Factors affecting heat production of rat 3Y1 fibroblasts in flow microcalorimetry

Quiescent 3Y1 cells in monolayer cultures were dispersed with trypsin-EDTA, suspended in various media, and the cellular heat production was measured in a flow-type microcalorimeter set at 37 degrees C. A linear relationship was found to exist between the number of cells applied to the microcalorimeter and the heat output. Increasing concentrations of bovine serum albumin (BSA) and of fetal calf serum (FCS) added in Dulbecco's modified Eagle's medium (DEM) enhanced the heat output to the same saturation level. Trypsin inhibitor added in DEM enhanced the heat output, but to a lower saturation level than FCS or BSA did, indicating that BSA has an activity to enhance cellular heat production by a mechanism other than neutralizing residual trypsin. The heat output was found to gradually decrease in the microcalorimeter. This reduction was not enhanced by a two-fold dilution of the medium (DEM plus FCS) with phosphate-buffered saline, indicating that this reduction is not caused by the depletion of nutrients and serum factors in the medium. Similarly, when cells were incubated for 155 or 220 min in suspension in DEM plus BSA at 37 degrees C and applied to the microcalorimeter, the heat output decreased. However, no significant reduction of the heat output was observed after holding the cells at 0 degree C in suspension for the same period. This and other facts suggest that depletion of O2 dissolved in the medium is involved in the gradual decrease in heat output.(ABSTRACT TRUNCATED AT 250 WORDS)     

The application of microcalorimetry to the assessment of metabolic efficiency in isolated rat hepatocytes

1. Heat output by suspensions of isolated rat hepatocytes was determined by using a modified batch-type microcalorimeter. 2. The ratio of O(2) uptake (determined polarographically) to heat output was used to assess the metabolic efficiency of isolated hepatocytes. 3. Cells from starved or fed rats incubated in either bicarbonate-buffered physiological saline containing gelatin, or bicarbonate-buffered physiological saline containing amino acids, serum albumin and glucose showed no significant difference with respect to the ratio of O(2) uptake to heat output. 4. For liver cells from 24h-starved rats, the addition of 10mm-dihydroxyacetone and 2.5mm-fructose significantly decreased the ratio of O(2) uptake to heat output from 1.94+/-0.05 in the controls to 1.52+/-0.04 and 1.54+/-0.01mumol/J respectively. 5. Glucagon (1mum), which slightly increased both O(2) uptake and heat output, did not significantly alter the ratio. 6. The addition of extracellular 10mm-NH(4)Cl and urease to provide an energetically wasteful cycle by ensuring hydrolysis of newly synthesized urea, lowered the ratio of O(2) uptake to heat output from 1.81+/-0.08 to 1.47+/-0.06mumol/J, indicating a reduced metabolic efficiency. 7. Metabolic efficiency in rats of different dietary regimen, age and genetically based obesity was also assessed. No differences in the ratio of O(2) uptake to heat output were found between liver cell suspensions prepared from rats maintained on colony diet and high-fat diet or sucrose-rich diet nor between animals ranging from 38 to 179 days of age. Comparison of the ratio of liver cell O(2) uptake to heat output between homozygote Zucker fa/fa obese rats and their lean littermates showed no significant difference. 8. It is concluded that the ratio of O(2) uptake to heat output for isolated hepatocytes is relatively constant unless perturbed by conditions that markedly enhance substrate cycling.     

Microcalorimetric investigation on the growth model and the protein yield of Bacillus thuringiensis

A novel microcalorimetric technique based on the bacterial heat output was applied to evaluate the special growth model, the protein expression and the generation time of Bacillus thuringiensis for the first time. The thermogenic curves of the aerobic metabolism of B. thuringiensis strains YBT-833, YBT-1520 and YBT-833-2-1 were determined by using an LKB-2277 BioActivity Monitor. The analysis of the thermogenic curves indicated both the mutant strain and the wild-type strains followed the same linear growth model during sporulation. The metabolism heat output revealed heat output was correlated to the yield of the insecticidal crystal proteins (ICPs) very well, the more protein product, and the less heat output. Based on the data acquired, we proposed that this method could be a useful tool in monitoring the fermentation of B. thuringiensis.     

Cell-cycle independent increase in heat production in response to growth factors in cultured rat fibroblasts: interpretation by continuum model

We measured the heat output from rat 3Y1 fibroblastic cells by stopped-flow method using a flow microcalorimeter. When the resting cells were stimulated to initiate DNA synthesis with growth factors, the heat output increased. Although cells normally progressed through S and G2 phases in the absence of any growth factor, cells increased the heat output in response to the growth factors during the progression through these phases. These results are consistent with the continuum model in which the preparation for the initiation of S phase occurs continuously and cumulatively between adjacent S phases not restricted in G1 phase.     

The redistribution of cardiac output in the dog during heat stress

In conscious Greyhound dogs, radioactive microsphere techniques have been used to measure cardiac output, its regional distribution, and proportion of the cardiac output passing through arteriovenous anastomoses (AVA's) in a thermoneutral environment and during severe heat stress. Heat stress resulted in a 74% increase in cardiac output and 4–6% of the cardiac output passed through AVA's. compared with about 1% under thermoneutral conditions: blood flow rate increased in skin of the lower legs and ears, tongue, maxillo turbinals, nasal mucosa, respiratory muscles and spleen, decreased in the thyroids, brain and spinal cord, and did not change significantly in the non-respiratory muscles, heart, pituitary, adrenals, kidneys, liver, stomach and intestines. Thus the circulatory requirements of the heat stressed dogs were met partly by an increase in cardiac output and partly by changes in its distribution. In contrast, the Merino sheep meets such a situation entirely by a redistribution of cardiac output. The present results may be taken as evidence that the Greyhound dog is less heat tolerant than the Merino sheep. The decreased brain blood flow during heat stress is similar to that which occurs in the sheep, but contrast with previous results obtained on anaestherized dogs. The less marked redistribution of cardiac output in the dog compared with the sheep, may explain the apparent difference in energy cost of panting in the two species.     

Investigation of growth and metabolism of Saccharomyces cerevisiae (baker's yeast) using microcalorimetry and bioluminometry

The heat evolution of aerated and non-aerated batch cultures of Saccharomyces cerevisiae (baker's yeast) in complex glucose medium was investigated by flow microcalorimetry. The course of heat output, substrate consumption and intracellular ATP concentration were extensively studied during the occurrence of an unexpected late peak. The results showed that the acetate could not be responsible for the occurrence of the late peak after the cessation of the growth. Enzyme induction and storage carbohydrate mobilization could be associated with this phenomenon. Linear relationships existed between initial glucose concentration, biomass concentration and total heat output and also between the log of viable cell numbers and the log of integrated heat output. A logistic equation was derived that fit the heat output curves. A model is proposed for predicting the biomass concentration from the power-time curves during the anaerobic growth of S. cerevisiae.     

Composting Process Control Based on Interaction Between Microbial Heat Output and Temperature

Rational composting process control involves the interrelated factors of heat output, temperature, ventilation, and water removal. The heat is released microbially at the expense of organic material; temperature is an effect and, because it is a determinant of microbial activity, it is also a cause of heat output; ventilation supplies oxygen and removes heat, mainly through the vaporization of water; water removal results from heat removal. These relationships were implemented in a field-scale process of static-pile configuration, using a mixture of sewage sludge and wood chips. Heat removal was matched to heat output through a temperature feedback control system, thereby maintaining biologically favorable temperatures. The observations indicate that fundamentally there are two kinds of composting systems: those that are and those that are not temperature self-limiting. The self-limiting system reaches inhibitive temperatures (>60°C) which debilitate the microbial community, suppressing decomposition, heat output, and water removal. In contrast, non-self-limiting temperatures (<60°C) support a robust community, promoting decomposition, heat output, and water removal.     

Hydration effects on thermoregulation and performance in the heat

During exercise, sweat output often exceeds water intake, producing a water deficit or hypohydration. The water deficit lowers both intracellular and extracellular fluid volumes, and causes a hypotonic-hypovolemia of the blood. Aerobic exercise tasks are likely to be adversely effected by hypohydration (even in the absence of heat strain), with the potential affect being greater in hot environments. Hypohydration increases heat storage by reducing sweating rate and skin blood flow responses for a given core temperature. Hypertonicity and hypovolemia both contribute to reduced heat loss and increased heat storage. In addition, hypovolemia and the displacement of blood to the skin make it difficult to maintain central venous pressure and thus cardiac output to simultaneously support metabolism and thermoregulation. Hyperhydration provides no advantages over euhydration regarding thermoregulation and exercise performance in the heat.     

Modelflow underestimates cardiac output in heat-stressed individuals

An estimation of cardiac output can be obtained from arterial pressure waveforms using the Modelflow method. However, whether the assumptions associated with Modelflow calculations are accurate during whole body heating is unknown. This project tested the hypothesis that cardiac output obtained via Modelflow accurately tracks thermodilution-derived cardiac outputs during whole body heat stress. Acute changes of cardiac output were accomplished via lower-body negative pressure (LBNP) during normothermic and heat-stressed conditions. In nine healthy normotensive subjects, arterial pressure was measured via brachial artery cannulation and the volume-clamp method of the Finometer. Cardiac output was estimated from both pressure waveforms using the Modeflow method. In normothermic conditions, cardiac outputs estimated via Modelflow (arterial cannulation: 6.1 ± 1.0 l/min; Finometer 6.3 ± 1.3 l/min) were similar with cardiac outputs measured by thermodilution (6.4 ± 0.8 l/min). The subsequent reduction in cardiac output during LBNP was also similar among these methods. Whole body heat stress elevated internal temperature from 36.6 ± 0.3 to 37.8 ± 0.4°C and increased cardiac output from 6.4 ± 0.8 to 10.9 ± 2.0 l/min when evaluated with thermodilution (P < 0.001). However, the increase in cardiac output estimated from the Modelflow method for both arterial cannulation (2.3 ± 1.1 l/min) and Finometer (1.5 ± 1.2 l/min) was attenuated compared with thermodilution (4.5 ± 1.4 l/min, both P < 0.01). Finally, the reduction in cardiac output during LBNP while heat stressed was significantly attenuated for both Modelflow methods (cannulation: -1.8 ± 1.2 l/min, Finometer: -1.5 ± 0.9 l/min) compared with thermodilution (-3.8 ± 1.19 l/min). These results demonstrate that the Modelflow method, regardless of Finometer or direct arterial waveforms, underestimates cardiac output during heat stress and during subsequent reductions in cardiac output via LBNP.     

Evidence for thermoregulatory behavior during self-paced exercise in the heat

The primary objective of this investigation was to test the hypothesis that voluntary reductions in exercise intensity in heat improve heat exchange between the body and the environment, and are thus thermoregulatory behaviors. This was accomplished by observing the conscious selection of exercise intensity and the accompanying thermal outcomes of eleven moderately active males when exposed to an uncompensably hot (UNCOMP) and a compensable (COMP) thermal environment. Evidence for thermoregulatory behavior was defined relative to the specific, pre-determined definition. Self-selected exercise intensity (power output) was unanimously reduced in UNCOMP over time and relative to COMP in all the subjects. These voluntary responses were found to modify metabolic heat production over time and therefore heat exchange between the body and the environment. Likewise, the observed reductions in power output were, at least in part, due to a conscious action, that was found to be inversely related to the total body heat storage and thermal discomfort. There was no evidence for thermoregulatory behavior in COMP. These data uniquely indicate that voluntary reductions in exercise intensity improves heat exchange over time, and therefore contributes to the regulation of body temperature. These findings suggest that reductions in exercise intensity in heat are, by definition, thermoregulatory behaviors.     

Microcalorimetric studies of Klebsiella aerogenes grown in chemostat culture. 3 Transient (non-steady) state

The increased power output resulting from the addition of small amounts of different substrates to glucose-limited chemostats depended on the added C-source; four types of substrate were recognised. The additional heat evolved increased linearly with the amount of added acetate, but not with glucose or pyruvate. Small amounts of uncouplers disturbed the steady-state power output, and the increased heat was related to the stimulation of the ATPase system. The enhanced power output on increasing the growth pH to 8 was associated with proton translocating ATPase activity.     

Utility of blood flow to the appendages in physiological control of heat exchange in reptiles

1. A heat transfer model was used to examine the possible sites for the cardiovascular control of heat exchange in ectothermic reptiles. 2. Predicted effects of changes in blood flow on heating and cooling remained constant or increased with mass. 3. Predicted sites at which changes in blood flow strongly affect heating and cooling rates differed between small (⩽1 kg) and large (⩾10 kg) reptiles. 4. In small reptiles (⩽1 kg) blood flow to appendages affected heating and cooling rates but blood flow to the torso had little effect on heat exchange. 5. In large animals (⩾10 kg) changing blood flow to either appendages or torso affected heat exchange; small changes in cardiac output have maximum effects when they occur at the appendages, but larger changes in cardiac output can achieve even larger effects by changing torso blood flow.     

Microcalorimetric measurements of tissue cells in vitro

A culture flask was designed for the microcalorimetric measurements of tissue cells by an MS 80 standard calvet microcalorimeter. Tissue cells cultured in this flask behaved in the same manner as in the common culture flask used in cytobiological studies. The thermograms of human adenocarcinoma gastric cells (SGc 7901) and HeLa cells were obtained. The heat output power of SGc 7901 cells continuously increased for 70 h with an initial cell number of 3.0 X 10(5). The thermogram was reproducible under strictly controlled conditions. The relationship between the heat output power and the number of SGc 7901 cells within 48 h was obtained. The heat output power was 40 pW/cell to 49 pW/cell when the cell number was in the range 4.5 X 10(5) to 10.4 X 10(5). It was 62.3 +/- 2.9 pW/cell for HeLa cells when the cell number was 6 X 10(5).     

Antigenic stimulation of lymphocytes I. Calorimetric exploration of metabolic responses

The rate of evolution of beat, an index of overall metabolic activity, has been measured for lymphocytes undergoing simple culture as well as in the presence of the specific antigen, DNP-BSA (dinitrophenylated bovine serum albumin), of the mitogenic lectin Con A (concanavalin A), and of inhibitors of various aspects of cell culture. Unstimulated lymphocytes evolve heat initially at a decreasing rate which stabilizes after 3 days of culture. Cells stimulated with antigen increase thermogenesis after 2 days of exposure to a maximum at 4–5 days, on a schedule that parallels increases in DNA synthesis. Cells stimulated with Con A show early increases in heat output which precede the onset of increased DNA synthesis. Inhibition of DNA synthesis alone does not significantly inhibit heat output, whereas inhibition of protein and RNA synthesis has a profound effect, as does interference with the structure of microfilaments with cytochalasin B. The completely synthetic multivalent high molecular weight antigen, PEO-DNP₈₀ (dinitrophenylated polyethylene oxide) is capable of abolishing the response of the cells to DNP-BSA and to Con A as well as of directly inhibiting the output of heat by the cells.     

Energy Production in Cardiac Isotonic Contractions

The energy output of rabbit papillary muscle is examined and it is shown that there is more energy liberated in an afterloaded isotonic contraction than in an "equivalent" isometric contraction. This statement holds true regardless of whether equivalence is based on the proposition that tension or the time integral of tension is the best index of muscle energy expenditure. Besides the external work performed there is additional heat production in isotonic contractions and this heat increases as the afterload is decreased. The additional heat is more evident when tension rather than the time integral of tension is made the determinant of energy expenditure. It is shown in single contractions that the rate of isotonic heat production, regardless of afterload size, never exceeds the heat rate recorded in an isometric contraction at the same initial length. Experiments reveal no simple linear correlation between isotonic energy output and contractile element work. Problems associated with the compartmentalization of the energy output of a contraction are discussed.     

Effect of heat stress on cardiac output and systemic vascular conductance during simulated hemorrhage to presyncope in young men

During moderate actual or simulated hemorrhage, as cardiac output decreases, reductions in systemic vascular conductance (SVC) maintain mean arterial pressure (MAP). Heat stress, however, compromises the control of MAP during simulated hemorrhage, and it remains unknown whether this response is due to a persistently high SVC and/or a low cardiac output. This study tested the hypothesis that an inadequate decrease in SVC is the primary contributing mechanism by which heat stress compromises blood pressure control during simulated hemorrhage. Simulated hemorrhage was imposed via lower body negative pressure (LBNP) to presyncope in 11 passively heat-stressed subjects (increase core temperature: 1.2 ± 0.2°C; means ± SD). Cardiac output was measured via thermodilution, and SVC was calculated while subjects were normothermic, heat stressed, and throughout subsequent LBNP. MAP was not changed by heat stress but was reduced to 45 ± 12 mmHg at the termination of LBNP. Heat stress increased cardiac output from 7.1 ± 1.1 to 11.7 ± 2.2 l/min (P < 0.001) and increased SVC from 0.094 ± 0.018 to 0.163 ± 0.032 l·min(-1)·mmHg(-1) (P < 0.001). Although cardiac output at the onset of syncopal symptoms was 37 ± 16% lower relative to pre-LBNP, presyncope cardiac output (7.3 ± 2.0 l/min) was not different than normothermic values (P = 0.46). SVC did not change throughout LBNP (P > 0.05) and at presyncope was 0.168 ± 0.044 l·min(-1)·mmHg(-1). These data indicate that in humans a cardiac output adequate to maintain MAP while normothermic is no longer adequate during a heat-stressed-simulated hemorrhage. The absence of a decrease in SVC at a time of profound reductions in MAP suggests that inadequate control of vascular conductance is a primary mechanism compromising blood pressure control during these conditions.     

Errors in calculating cardiac output due to administration of perfluorochemicals

Intravenous administration of perfluorochemicals (PFC) will alter the density (rho)B, the gravimetric specific heat (c)B, and the volumetric specific heat (rho c)B of blood. Changes in hematocrit also influence (rho c)B. The calibration constant employed in the determination of cardiac output (CO) by thermal dilution depends inversely on (rho c)B. We estimate the effect of addition of PFC and changes in hematocrit on (rho c)B. Consider blood to be a mixture of red cells, emulsified PFC particles, and plasma. This leads to the equation: (rho c)cB = 0.96 - 0.11Hct - 0.48Fct. Here Hct and Fct are the fractional volume concentrations of red blood cells and PFC, and (rho c)cB is the calculated specific heat based on the actual composition of blood. CO can be corrected for changes in (rho c)B by the equation: (CO)c = [(rho c)sB/(rho c)cB](CO)o. Here (CO)o is the observed cardiac output, (rho c)sB is the standard specific heat of blood used in the calculation of (CO)o, and (CO)c is the corrected cardiac output. We have observed laboratory situations where the correction factors have been as high as 10%.     

Microcalorimetric study of the action of Ce(III) ions on the growth of E. coli

A microcalorimetric technique based on bacterial heat output was used to evaluate the action of Ce(III) ions on the growth of Escherichia coli. The power-time curves of the growth metabolism of the bacteria were studied in the presence and absence of Ce(III) by means of a LKB-2277 Bioactivity Monitor, by a stopped-flow method at 37°C. For evaluation of the results, the maximum power, P _max, the growth rate constant k, and the heat effects Q _log, Q _stat, and Q _tot for the log phase, the stationary phase, and total heat output, respectively, were determined. For comparison, a spectrophotometer was used to estimate the number of cells in the liquid culture. The shape of the bacteria was examined by electron microscopy. We concluded that the presence of cerium ions at concentrations below 350 μg/mL have a stimulatory effect on the growth of E. coli, whereas concentrations at or above 400 μg/mL may have an inhibitory effect.     

Role of catalase in myocardial protection against ischemia in heat shocked rats

It was recently reported that in rats exposure to heat shock leads to appearance of a myocardial heat shock protein (HSP 70) and to an increase in myocardial catalase activity. This correlated with an improvement in post-ischemic function either in Langendorff-perfused hearts after low-flow ischemia or in working hearts after short-term, no-flow ischemia. We investigated the effect of the same hyperthermic treatment on functional recovery from no-flow ischemia of various durations in isolated working rat hearts performing at high or low external workloads. Rats were heated to core temperature of 42° C for 15 min. No significant protein oxidation (% oxidized methionine) was observed 2.5 hr after treatment. A protein with migration characteristics similar to HSP 70 was observed in hearts of heat shocked rats 24 hr after this treatment while their myocardial catalase activity was not increased. Hearts of similarly treated rats were excised 24 hr after hyperthermia and perfused in a working mode with Krebs-Henseleit buffer (1.25 mM Ca²⁺, 11 mM glucose). At 15 cm H₂O preload and 100 cm H₂O afterload after 30 min no-flow ischemia, control hearts recovered to 36.9%, 2%, 47.6%, and 21.5% of the preischemic values of heart rate-peak systolic pressure product (RPP), aortic output, coronary flow, and cardiac output, respectively. After only 25 min of ischemia the respective recovered values were 61.6%, 11.5%, 58.7%, and 33.5%. Throughout the recovery period these hemodynamic values were consistently higher in hearts of heat shocked animals than in those of control hearts but the differences were not statistically significant. After 25 min ischemia only 2 out of 7 control hearts recovered some aortic output, whereas in the heat shocked animals all 5 hearts recovered. After only 20 min of no-flow ischemia and at a lower workload (12.5 cm H₂O preload and 75 cm H₂O afterload), control hearts recovered to 85.1% of RPP, 54.1% of aortic output, and 68.3% of cardiac output. None of these variables was significantly improved by heat shock pretreatment. In summary, we were unable to demonstrate a similar degree of protective effect of heat shock pretreatment as compared to other reports where both HSP 70 and increased catalase activity were present. The reason(s) could be related to lack of induction of myocardial catalase activity in our study.     

Human power output during repeated sprint cycle exercise: the influence of thermal stress

Thermal stress is known to impair endurance capacity during moderate prolonged exercise. However, there is relatively little available information concerning the effects of thermal stress on the performance of high-intensity short-duration exercise. The present experiment examined human power output during repeated bouts of short-term maximal exercise. On two separate occasions, seven healthy males performed two 30-s bouts of sprint exercise (sprints I and II), with 4 min of passive recovery in between, on a cycle ergometer. The sprints were performed in both a normal environment [18.7 (1.5) degrees C, 40 (7)% relative humidity (RH; mean SD)] and a hot environment [30.1 (0.5) degrees C, 55 (9)% RH]. The order of exercise trials was randomised and separated by a minimum of 4 days. Mean power, peak power and decline in power output were calculated from the flywheel velocity after correction for flywheel acceleration. Peak power output was higher when exercise was performed in the heat compared to the normal environment in both sprint I [910 (172) W vs 656 (58) W; P < 0.01] and sprint II [907 (150) vs 646 (37) W; P < 0.05]. Mean power output was higher in the heat compared to the normal environment in both sprint I [634 (91) W vs 510 (59) W; P < 0.05] and sprint II [589 (70) W vs 482 (47) W; P < 0.05]. There was a faster rate of fatigue (P < 0.05) when exercise was performed in the heat compared to the normal environment. Arterialised-venous blood samples were taken for the determination of acid-base status and blood lactate and blood glucose before exercise, 2 min after sprint I, and at several time points after sprint II. Before exercise there was no difference in resting acid-base status or blood metabolites between environmental conditions. There was a decrease in blood pH, plasma bicarbonate and base excess after sprint I and after sprint II. The degree of post-exercise acidosis was similar when exercise was performed in either of the environmental conditions. The metabolic response to exercise was similar between environmental conditions; the concentration of blood lactate increased (P < 0.01) after sprint I and sprint II but there were no differences in lactate concentration when comparing the exercise bouts performed in a normal and a hot environment. These data demonstrate that when brief intense exercise is performed in the heat, peak power output increases by about 25% and mean power output increases by 15%; this was due to achieving a higher pedal cadence in the heat.