Estimation of the core temperature control during ambient temperature changes and the influence of circadian rhythm and metabolic conditions in mice

It has been speculated that the control of core temperature is modulated by physiological demands. We could not prove the modulation because we did not have a good method to evaluate the control. In the present study, the control of core temperature in mice was assessed by exposing them to various ambient temperatures (T_a), and the influence of circadian rhythm and feeding condition was evaluated. Male ICR mice (n=20) were placed in a box where T_a was increased or decreased from 27 °C to 40 °C or to −4 °C (0.15 °C/min) at 0800 and 2000 (daytime and nighttime, respectively). Intra-abdominal temperature (T_core) was monitored by telemetry. The relationship between T_core and T_a was assessed. The range of T_a where T_core was relatively stable (range of normothermia, RNT) and T_core corresponding to the RNT median (regulated T_core) were estimated by model analysis. In fed mice, the regression slope within the RNT was smaller in the nighttime than in the daytime (0.02 and 0.06, respectively), and the regulated T_core was higher in the nighttime than in the daytime (37.5 °C and 36.0 °C, respectively). In the fasted mice, the slope remained unchanged, and the regulated T_core decreased in the nighttime (0.05 and 35.9 °C, respectively), while the slopes in the daytime became greater (0.13). Without the estimating individual thermoregulatory response such as metabolic heat production and skin vasodilation, the analysis of the T_a–T_core relationship could describe the character of the core temperature control. The present results show that the character of the system changes depending on time of day and feeding conditions.     

The magnitude of physical exercise-induced hyperthermia is associated with changes in the intestinal permeability and expression of tight junction genes in rats

We investigated whether the magnitude of exercise-induced hyperthermia influences intestinal permeability and tight junction gene expression. Twenty-nine male Wistar rats were divided into four groups: rest at 24 °C and exercise at 13 °C, 24 °C or 31 °C. The exercise consisted of a 90-min treadmill run at 15 m/min, and different ambient temperatures were used to produce distinct levels of exercise-induced hyperthermia. Before the experimental trials, the rats were treated by gavage with diethylenetriaminepentaacetic acid labeled with technetium-99 metastable as a radioactive probe. The rats' core body temperature (T_CORE) was measured by telemetry. Immediately after the trials, the rats were euthanized, and the intestinal permeability was assessed by measuring the radioactivity of blood samples. The mRNA levels of occludin and zonula occludens-1 (ZO-1) genes were determined in duodenum samples. Exercise at 24 °C increased T_CORE to values close to 39 °C, without changing permeability compared with the resting trial at the same environment. Meanwhile, rats’ T_CORE exceeded 40 °C during exercise at 31 °C, leading to greater permeability relative to those observed after exercise in the other ambient temperatures (e.g., 0.0037%/g at 31 °C vs. 0.0005%/g at 13 °C; data expressed as medians; p < 0.05). Likewise, the rats exercised at 31 °C exhibited higher mRNA levels of ZO-1 and occludin genes than the rats exercised at 24 °C or 13 °C. The changes in permeability and gene expression were positively and significantly associated with the magnitude of hyperthermia. We conclude that marked hyperthermia caused by exercise in the warmer environment increases intestinal permeability and mRNA levels of tight junction genes.     

Hibernation patterns of Turkish hamsters: influence of sex and ambient temperature

Turkish hamsters (Mesocricetus brandti) are a model organism for studies of hibernation, yet a detailed account of their torpor characteristics has not been undertaken. This study employed continuous telemetric monitoring of body temperature (T _b) in hibernating male and female Turkish hamsters at ambient temperatures (T _as) of 5 and 13 °C to precisely characterize torpor bout depth, duration, and frequency, as well as rates of entry into and arousal from torpor. Hamsters generated brief intervals of short (<12 h), shallow test bouts (T _b > 20 °C), followed by deep torpor bouts lasting 4–6 days at T _a = 5 °C and 2–3 days at T _a = 13 °C. Females at T _a = 5 °C had longer bouts than males, but maintained higher torpor T _b; there were no sex differences at T _a = 13 °C. Neither body mass loss nor food intake differed between the two T _as. Hamsters entered torpor primarily during the scotophase (subjective night), but timing of arousals was highly variable. Hamsters at both T _as generated short, shallow torpor bouts between deep bouts, suggesting that this species may be capable of both hibernation and daily torpor.     

Effect of change in ambient temperature on core temperature during the daytime

In this study, the hypothesis is tested that continuous increases in ambient temperature (T_a) during daytime would give elevated core and skin temperatures, and consequently better thermal sensation and comfort. Rectal temperature (T_re), skin temperatures and regional dry heat losses at 7 sites were continuously measured for 10 Japanese male subjects in three thermal conditions: cond. 1, stepwise increases in T_a from 26 °C at 9 h00 to 30 °C at 18 h00; cond. 2, steady T_a at 28 °C from 9 h00 to 18 h00 and cond. 3, stepwise decreases in T_a from 30 °C at 9 h00 to 26 °C at 18 h00. Oxygen consumption was measured and thermal sensation and comfort votes were monitored at 15 min intervals. Body weight loss was measured at 1 h intervals. While T_re increased continuously in the morning period in any condition, it increased to a significantly greater (p?<?0.05) 36.9?±?0.3 °C at 18 h00 in cond. 1 relative to 36.7?±?0.28 °C in Cond. 2 and 36.5?±?0.37 °C in cond. 3. Better thermal comfort was observed in the afternoon and the evening in Cond.1 as compared with the other 2 conditions. Thus, a progressive and appropriate increase in T_a may induce optimal cycle in core temperature during daytime, particularly for a resting person.     

Hypohydration increases the plasma catecholamine response to moderate exercise in the dog (Canis)

1. The effects of hypohydration produced by 48 hr water deprivation were examined in dogs during moderate treadmill exercise at an ambient temperature (T_a) of 21°C.2. Hypohydration caused a significant elevation in plasma levels of adrenaline (A), proteins (pp) and osmolality (pOsm).3. During 1 hr of running, plasma concentrations of adrenaline (A) and noradrenaline (NA) rose significantly, whilst no change in these hormones occurred in dogs hydrated ad libitum.4. The results suggest that hypovolemia in the dog may be a sufficient stimulus to intensify the sympatho-adrenal response to moderate exercise performed at a room T_a.     

Brain temperature regulation of panting and non-panting pigeons exposed to extreme thermal conditions

• 1.1. Brain (hypothalamic), skin and body temperatures were measured in hand-reared acclimated (Acc, n = 5) and non-acclimated (NAcc, n =7) rock pigeons (Columba livia, mean body mass 237 g) exposed to increasing ambient temperatures (T_a) (30–60°C) and low humidities.
• 2.2. In non-panting Acc birds, brain temperature gradually increased from 40.1 ± 0.4°C at 30°C to 41.2 ± 0.4°C at 60°C T_a. A mean body temperature (T_b) of 41.2 ± 0.2°C was measured at T_a up to 50°C; an increase of 1.1°C was observed at 60°C (T_b 42.2 ±0.6°C).
• 3.3. In Acc panting birds exposed for 2 hr to 60°C, T_hy was 41.9 ± 0.8°C and T_s was somewhat (but insignificantly) higher, i.e., 42.2 ± 0.7°C. It looks as if both values were increased as a result of a slight hyperthermia that developed (T_b = 43.5 ± 0.9°C).
• 4.4. The significance of the present results for evaluating neuronal thermoresponsiveness of birds' hypothalamus is discussed.

     

Sex difference in thermal preference of adult mice does not depend on presence of the gonads

Background

The thermoneutral zone (TNZ) is a species-specific range of ambient temperature (T _a), at which mammals can maintain a constant body temperature with the lowest metabolic rate. The TNZ for an adult mouse is between 26 and 34 °C. Interestingly, female mice prefer a higher T _a than male mice although the underlying mechanism for this sex difference is unknown. Here, we tested whether gonadal hormones are dominant factors controlling temperature preference in male and female mice.

Methods

We performed a temperature preference test in which 10-week-old gonadectomized and sham-operated male and female C57BL/6J mice were allowed to choose to reside at the thermoneutral cage of 29 °C or an experimental cage of 26, 29, or 32 °C.

Results

All mice preferred a T _a higher than 26 °C, especially in the inactive phase. Choosing between 29 and 32 °C, female mice resided more at 32 °C while male mice had no preference between the temperatures. Hence, the preferred T _a for female mice was significantly higher (0.9?±?0.2 °C) than that for male mice. However, gonadectomy did not influence the T _a preference.

Conclusions

Female mice prefer a warmer environment than male mice, a difference not affected by gonadectomy. This suggests that thermal-sensing mechanisms may be influenced by sex-specific pathways other than gonadal factors or that the thermoregulatory set point has already been determined prior to puberty.

     

Physiological responses of naloxone-treated pigeons to changes in ambient temperature

1. In pigeons given single intramuscular injection of naloxone, the heart rate (HR), breathing frequency (BF), oxygen consumption (VO₂), cloacal temperature (T_c) and foot temperature (T_f) were monitored during gradual lowering of the ambient temperature (T,) from 34°C to 6° in 6 hr.2. The two doses of naloxone tested (2 mg and 5 mg/kg b.w.) had an inhibitory effect on HR, the effect being greater with the higher dose as well as with the fall in T_a.3. The higher dose showed a tendency to have a stimulatory effect on BF in T_a above 22°C and an inhibitory effect in T_a below 22°C. With the lower dose, BF remained unaltered except in T_a below 12°C during which it showed a trend toward a decrease.4. VO₂ decreased with the higher dose, the extent of decrease being greater with drop in T_a. With the lower dose, VO₂ was not affected at or below T_a 26°C, but showed a trend toward an increase at T_a above 26°.5. The higher dose produced hyperthermia when T_a was below 14°C, whereas with the lower dose, T_c showed no significant change except for a slight drop at T_a 6°C.6. T_fwas not significantly affected by naloxone treatment.7. It is suggested that these effects were caused by the inhibition of endorphine-mediated catecholamine release by naloxone.     

Thermal responses of an insect subjected to temperature variations

Temperature responses of the cockroach, Blaberus craniifer, to rapid changes of ambient temperature (T_a) have been studied. In static conditions at T_a = 27°C the body-to-ambient temperature difference was only 0.10 ± 0.07°C. Two test situations were used, either a ramp increase of T_a from 27 to 31°C (0.1°C/min) or “step” changes from 27 to 28°C and back (0.5°C/min). In both cases body temperature closely followed Newtonian model, the body time constants measured in various conditions being very similar: 543 ± 99 sec in ramp tests, 550 ± 68 sec and 542 ± 124 sec in rising and falling step tests respectively. It is concluded that in spite of evident differences between the cockroach and an inert solid, the Newtonian model adequately represents the thermal responses of this insect to moderate changes in ambient temperature.     

Determinants of bovine thermal response to heat and solar radiation exposures in a field environment

Continuous exposure of cattle to summer heat in the absence of shade results in significant hyperthermia and impairs growth and general health. Reliable predictors of heat strain are needed to identify this condition. A 12-day study was conducted during a moderate summer heat period using 12 Angus x Simmental (Bos taurus) steers (533 ± 12 kg average body weight) to identify animal and ambient determinations of core body temperature (T _core) and respiration rate (RR) responses to heat stress. Steers were provided standard diet and water ad libitum, and implanted intraperitoneally with telemetric transmitters to monitor T _core hourly. Visual count of flank movement at 0800 and 1500 hours was used for RR. Dataloggers recorded air temperature (T _a), and black globe temperatures (T _bg) hourly to assess radiant heat load. Analysis was across four periods and 2 consecutive days averaged within each period. Average T _a and T _bg increased progressively from 21.7 to 30.3°C and 25.3 to 34.0°C, respectively, from the first to fourth periods. A model utilizing a quadratic function of T _a explained the most variation in T _core (R ² = 0.56). A delay in response from 1 to 3 h did not significantly improve R ² for this relationship. Measurements at 0800 and 1500 hours alone are sufficient to predict heat strain. Daily minimum core body temperature and initial 2-h rise in T _a were predictors of maximum core temperature and RR. Further studies using continuous monitoring are needed to expand prediction of heat stress impact under different conditions.     

Hypothalamic Temperature of Rats Subjected to Treadmill Running in a Cold Environment

Different strategies for cooling the body prior to or during physical exercise have been shown to improve prolonged performance. Because of ethical and methodological issues, no studies conducted in humans have evaluated the changes in brain temperature promoted by cooling strategies. Therefore, our first aim sought to measure the hypothalamic temperature (T_hyp) of rats subjected to treadmill running in a cold environment. Moreover, evidence suggests that T_hyp and abdominal temperature (T_abd) are regulated by different physiological mechanisms. Thus, this study also investigated the dynamics of exercise-induced changes in T_hyp and T_abd at two ambient temperatures: 25°C (temperate environment) and 12°C (cold). Adult male Wistar rats were used in these experiments. The rats were implanted with a guide cannula in the hypothalamus and a temperature sensor in the abdominal cavity. After recovery from this surgery, the rats were familiarized with running on a treadmill and were then subjected to the two experimental trials: constant-speed running (20 m/min) at 12°C and 25°C. Both T_hyp and T_abd increased during exercise at 25°C. In contrast, T_hyp and T_abd remained unchanged during fatiguing exercise at 12°C. The temperature differential (i.e., T_hyp - T_abd) increased during the initial min of running at 25°C and thereafter decreased toward pre-exercise values. Interestingly, external cooling prevented this early increase in the temperature differential from the 2^nd to the 8^th min of running. In addition, the time until volitional fatigue was higher during the constant exercise at 12°C compared with 25°C. Together, our results indicate that T_hyp and T_abd are regulated by different mechanisms in running rats and that external cooling affected the relationship between both temperature indexes observed during exercise without environmental thermal stress. Our data also suggest that attenuated hypothalamic hyperthermia may contribute to improved performance in cold environments.     

Modeling seed germination in Melisa officinalis L. in response to temperature and water potential

Seed germination is greatly influenced by both temperature (T) and water potential (ψ) and these factors largely determine germination rate (GR) in the field. Quantitative information about T and ψ effects on seed germination in lemon balm (Melisa officinalis L.) is scarce. The main objective of this study was to quantify seed germination responses of lemon balm to T and ψ, and to determine cardinal temperatures in a laboratory experiment. A segmented model was used to describe the effects of ψ (i.e., T) on GR and other germination parameters. The segmented model estimates were 7.2 °C for base (T _b), 28.9 °C for optimum (T _o), 40.1 °C for ceiling temperature (T _c) and 1.64 physiological days (f _o) (equivalent to a GR_max of 0.610 d^?1 and a thermal time of 35.6 °C days) to reach 50 % maximum germination in the control (0 MPa) treatment (R ² = 0.99, RMSE = 0.005 day^?1). The inherent maximum rate of germination (days) was calculated by the [GR_max = 1/f _o] model. ψ affected cardinal temperatures. From 0 to ?0.76 MPa, when ψ increased, T _b was a constant 7.2 °C to ?0.38 MPa and increased linearly to 20.1 °C as ψ decreased. T _o and f _o increased linearly from 28.9 to 30 °C, and from 1.64 to 5.4 day^?1, respectively as ψ decreased. However, there was no signification difference in T _o as ψ decreased nor did T _c decrease from 40.1 to 35 °C as ψ decreased. T _b, T _c and GR_max were the sole parameters affected by ψ and could be used to characterize differences between ψ treatments with respect to GR at various Ts. Therefore, the segmented model and its parameters can be used in lemon balm germination simulation models.     

Metabolic rate and body temperature of adult and juvenile hyrax (Procavia capensis)

• 1.1. Resting metabolic rates (RMR) below thermoneutrality in adult hyrax acclimated to 26, 15 and 10°C remained unchanged, i.e. thermal conductance (K) remained constant.
• 2.2. Conductance in juveniles decreased with acclimation to lower ambient temperatures (T_a).
• 3.3. Body temperature (T_b) dropped by 3.8°C in adults exposed to T_a of 30 – 5°C. The decrease was constant.
• 4.4. Body temperature fell by 1.5°C in juveniles exposed to T_a of 30 – 20°C but stabilized between 20 and 5°C.
• 5.5. The labile T_b, associated with behavioural strategies and lower than predicted RMR, can be seen as an energy-conserving mechanism of particular importance during winter conditions.

     

Changes in exercise and post-exercise core temperature under different clothing conditions

 This study evaluates the effect of different levels of insulation on esophageal (T _es) and rectal (T _re) temperature responses during and following moderate exercise. Seven subjects completed three 18-min bouts of treadmill exercise (75% VO_2max, 22°C ambient temperature) followed by 30 min of recovery wearing either: (1) jogging shoes, T-shirt and shorts (athletic clothing); (2) single-knit commercial coveralls worn over the athletic clothing (coveralls); or (3) a Canadian Armed Forces nuclear, bacteriological and chemical warfare protective overgarment with hood, worn over the athletic clothing (NBCW overgarment). T _es was similar at the start of exercise for each condition and baseline T _re was ∼0.4°C higher than T _es. The hourly equivalent rate of increase in T _es during the final 5 min of exercise was 1.8°C, 3.0°C and 4.2°C for athletic clothing, coveralls and NBCW overgarment respectively (P<0.05). End-exercise T _es was significantly different between conditions [37.7°C (SEM 0.1°C), 38.2°C (SEM 0.2°C and 38.5°C (SEM 0.2°C) for athletic clothing, coveralls and NBCW overgarment respectively)] (P<0.05). No comparable difference in the rate of temperature increase for T _re was demonstrated, except that end-exercise T _re for the NBCW overgarment condition was significantly greater (0.5°C) than that for the athletic clothing condition. There was a drop in T _es during the initial minutes of recovery to sustained plateaus which were significantly (P<0.05) elevated above pre-exercise resting values by 0.6°C, 0.8°C and 1.0°C, for athletic clothing, coveralls, and NBCW overgarment, respectively. Post-exercise T _re decreased very gradually from end-exercise values during the 30-min recovery. Only the NBCW overgarment condition T _re was significantly elevated (0.3°C) above the athletic clothing condition (P<0.05). In conclusion, T _es is far more sensitive in reflecting the heat stress of different levels of insulation during exercise and post-exercise than T _re. Physiological mechanisms are discussed as possible explanations for the differences in response. Received: 30 June 1998 / Accepted: 19 February 1999     

Energy metabolism and body temperature in 13 sunbird species (Nectariniidae)

• 1.1. Diurnal cycles of body temperature, T_b, and energy metabolism, M, at different ambient temperatures (T_a: +5 −+ 32°C) were tested in 13 sunbird species from various habitats and of different body masses (5.2–14.2 g) including one of the smallest passerines, Aethopyga christinae.
• 2.2. Resting M-level (night) reaches T_a-dependent mean values of 54% (+5°C) and 49% (+25°C) of activity M-levels (day). Expected level is ca 75%.
• 3.3. Resting metabolic rate of sunbirds lies within the range of theoretically expected values for birds.
• 4.4. Mean linear metabolism-weight regression of the night values follows: M = 0.102 × W^0.712 (M = energy metabolism in kJ/hr and W = body mass in g).
• 5.5. Thermal conductances, T_c, are lower (−24%) than the predicted values. This is caused by a decrease of T_b at low T_a. Mean nocturnal T_c is 3.2 J/g × hr × °C, mean day-time value is 4.3 J/g × hr × °C.
• 6.6. The zone of thermoneutrality is, in most species, within a T_a-range of 24–28°C.
• 7.7. Normal day and night levels of T_b are in the same range as reported for other birds of the same weight class. T_b decreases slightly with falling T_a (partial heterothermia). Lowest recorded T_b was 34.2°C.
• 8.8. No species tested showed any sign of torpor at night, independent of T_a, body mass or habitat origin.

     

Conventional and novel body temperature measurement during rest and exercise induced hyperthermia

Despite technological advances in thermal sensory equipment, few core temperature (T_CORE) measurement techniques have met the established validity criteria in exercise science. Additionally, there is debate as to what method serves as the most practically viable, yet upholds the proposed measurement accuracy. This study assessed the accuracy of current and novel T_CORE measurement techniques in comparison to rectal temperature (T_REC) as a reference standard. Fifteen well-trained subjects (11 male, 4 female) completed 60 min of exercise at an intensity equating to the lactate threshold; measured via a discontinuous exercise test. T_REC was significantly elevated from resting values (37.2±0.3 °C) at the end of moderate intensity exercise (39.6±0.04 °C; P=0.001). Intestinal telemetric pill (T_PILL) temperature and temporal artery temperature (T_TEM) did not differ significantly from T_REC at rest or during exercise (P>0.05). However, aural canal temperature (T_AUR) and thermal imaging temperature (T_IMA) were both significantly lower than T_REC (P<0.05). Bland Altman analysis revealed only T_PILL was within acceptable limits of agreement (mean bias; 0.04 °C), while T_TEM, T_AUR and T_IMA demonstrated mean bias values outside of the acceptable range (>0.27 °C). Against T_REC, these results support the use of T_PILL over all other techniques as a valid measure of T_CORE at rest and during exercise induced hyperthermia. Novel findings illustrate that T_IMA (when measured at the inner eye canthus) shows poor agreement to T_REC during rest and exercise, which is similar to other ‘surface’ measures.     

Body temperature variation in free-living and food-deprived yellow-necked mice sustains an adaptive framework for endothermic thermoregulation

In many mammalian species, variation in body temperature (T_b) exceeds the values suitable for defining homeothermy, making it justifiable and even necessary to resort to the term “heterothermic”. However, T_b data are only available for ca. 1% of extant mammalian species. We investigated variations in T_b in wild free-living and experimentally food-deprived yellow-necked mice Apodemus flavicollis, during the temperate-zone autumn-winter period. In line with the adaptive framework for endothermic thermoregulation, we hypothesised that T_b in the mice should be adjustable with the energetic cost-benefit trade-off associated with maintaining homeothermy. In laboratory conditions, mice clearly entered a state of daily torpor when food-deprived. Our study thus makes it clear that A. flavicollis is a heterothermic species in which food deprivation results in switching between endothermic and poikilothermic thermoregulation. We also assumed that, in free-living mice, heterothermy increases with elevated environmental challenges, e.g. when the ambient temperature (T_a) decreases. Consistent with this was the inverse correlation noted between variation in T_b in free-living mice and T_a, with most individuals clearly becoming torpid when T_a decreases below 0 °C. It is the increased cost of food hoarding under cold conditions that most likely triggers a state of torpor as a last result. Overall, our study indicates that yellow-necked mice can provide a further example of species sustaining an adaptive framework for endothermic thermoregulation.     

Body temperature in the mouse,hamster, and rat exposed to radiofrequency radiation: An interspecies comparison

• 1.1.|Colonic temperatures of BALB/c and CBA/J mice, golden hamsters, and Sprague-Dawley rats were taken immediately after exposure for 90 min to radiofrequency (RF) radiation.
• 2.2.|Exposures were made in 2450 MHz (mouse and hamster) or 600 MHz (rat) waveguide exposure systems while the dose rate, specific absorption rate (SAR), was continuously recorded. Experiments were performed on naive, unrestrained animals at ambient temperatures (T_a) of 20 and 30°C.
• 3.3.|Body mass and T_a) were found to be significant factors in influencing the threshold SAR for the elevation of colonic temperature. The threshold SARs at T_a's of 20 and 30°C were respectively: 27.5 and 12.1 W/kg for the BALB/c mouse; 40.7 and 8.5 W/kg for the CBA/J mouse; 8.7 and 0.61 W/kg for the golden hamster; and 1.58 and 0.4 W/kg for the Sprague-Dawley rat.
• 4.4.|The relationship between threshold SAR or SAR for a 1.0°C elevation in colonic temperature vs body mass were linearly and inversely related on a double logarithmic plot. The results of this study suggest that the thermoregulatory sensitivity to RF radiation in these rodent species is heavily dependent on body mass and T_a.

     

Growth of Kluyveromyces marxianus and formation of ethyl acetate depending on temperature

Conversion of lactose into ethyl acetate by Kluyveromyces marxianus allows economic reuse of whey-borne sugar. The high volatility of ethyl acetate enables its process-integrated recovery by stripping. This stripping is governed by both the aeration rate and the partition coefficient, K _EA,L/G. Cultivation at elevated temperatures should decrease the K _EA,L/G value and thus favor stripping. K. marxianus DSM 5422 as a potent producer of ethyl acetate was cultivated aerobically in whey-borne media for studying temperature-dependent growth and ester formation. Shake flask cultivation proved thermal tolerance of this yeast growing from 7 to 47 °C with a maximum rate of 0.75 h^?1 at 40 °C. The biomass yield was 0.41 g/g at moderate temperatures while low and high temperatures caused distinct drops. The observed μ-T and Y _X/S-T dependencies were described by mathematical models. Further cultivations were done in an 1-L stirred reactor for exploring the effect of temperature on ester synthesis. Cultivation at 32 °C caused significant ester formation (Y _EA/S?=?0.197 g/g) while cultivation at 42 °C suppressed ester synthesis (Y _EA/S?=?0.002 g/g). The high temperature affected metal dissolution from the bioreactor delivering iron for yeast growth and preventing ester synthesis. Cultivation at 32 °C with a switch to 42 °C at the onset of ester synthesis allowed quick and efficient ester production (Y _EA/S?=?0.289 g/g). The high temperature lowered the K _EA,L/G value from 78 to 44 L/L which heightened the gas-phase ester concentration (favoring ester recovery) without increasing the liquid-phase concentration (avoiding product inhibition).