Rise In Core Temperature Research Articles

Effects of Heat Removal Through the Hand on Metabolism and Performance During Cycling Exercise in the Heat

This two-part study tested the hypotheses that the use of a new cooling device, purported to extract heat from the body core through the palm of the hand, would (a) attenuate core temperature rise during submaximal exercise in the heat, thereby suppressing exercise-associated metabolic changes, and (b) facilitate a higher sustained workload, thus shortening the completion time of a time-trial performance test. In Study 1, 8 male triathletes (age 27.9 +/- 2.0 yrs, mass 77.2 +/- 3.1 kg, VO2peak 59.0 +/- 4.1 ml x min(-1) x kg(-1)) cycled for 1 hr at the same absolute workload (approximately 60% VO2peak) in a heated room (31.9 +/- 0.1 degrees C, 24 +/- 1% humidity) on two occasions counterbalanced for cooling (C) or noncooling (NC). In Study 2, 8 similar subjects (age 26.9 +/- 2.0 yrs, mass 75.2 +/- 3.7 kg, VO2peak 54.1 +/- 3.1 ml x min(-1) x kg(-1)) performed two 30-km cycling time-trial performance tests under the same conditions (C(T), NC(T)). In Study 1, cooling attenuated the rise in tympanic temperature (T(TY)) (1.2 +/- 0.2 vs. 1.8 +/- 0.2 degrees C; p < 0.01) and lowered mean oxygen consumption (VO2, 2.4 +/- 0.1 vs. 2.7 +/- 0.1 L x min(-1); p < 0.05) and blood lactate (1.7 +/- 0.2 vs. 2.2 +/- 0.2 mmol x L(-1); p < 0.01) during exercise. There were no significant differences in respiratory exchange ratio (RER), blood glucose, heart rate (HR), face temperature (T(F)), or back temperature (T(B)) between NC and C. In Study 2, time to complete 30 km was 6 +/- 1% less with cooling than without cooling (60.9 +/- 2.0 vs. 64.9 +/- 2.6 min; p < 0.01). During the last 20% of C(T), subjects sustained a workload that was 14 +/- 5% (p = 0.06) higher than NC(T) at the same T(TY) and HR. Heat extraction through the hand during cycle ergometer exercise in the heat can (a) lower T(TY), lactate concentration, and VO2 during a submaximal set-workload test and (b) reduce the time it takes to complete a 30-km time-trial test.

Effects of two cooling strategies on thermoregulatory responses of tetraplegic athletes during repeated intermittent exercise in the heat

Athletes with spinal cord injury (SCI), and in particular tetraplegia, have an increased risk of heat strain and consequently heat illness relative to able-bodied individuals. Strategies that reduce the heat strain during exercise in a hot environment may reduce the risk of heat illness. To test the hypotheses that precooling or cooling during intermittent sprint exercise in a heated environment would attenuate the rise in core temperature in tetraplegic athletes, eight male subjects with SCI (lesions C(5)-C(7); 2 incomplete lesions) undertook four heat stress trials (32.0 +/- 0.1 degrees C, 50 +/- 0.1% relative humidity). After assessment of baseline thermoregulatory responses at rest for 80 min, subjects performed three intermittent sprint protocols for 28 min. All trials were undertaken on an arm crank ergometer and involved a no-cooling control (Con), 20 min of precooling (Pre), or cooling during exercise (Dur). Trials were administered in a randomized order. After the intermittent sprint protocols, mean core temperature was higher during Con (37.3 +/- 0.3 degrees C) compared with Pre and Dur (36.5 +/- 0.6 degrees C and 37.0 +/- 0.5 degrees C, respectively; P < 0.01). Moreover, perceived exertion was lower during Pre (13 +/- 2; P < 0.01) and Dur (12 +/- 1; P < 0.01) compared with Con (14 +/- 2). These results suggest that both precooling and cooling during intermittent sprint exercise in the heat reduces thermal strain in tetraplegic athletes. The cooling strategies also appear to show reduced perceived exertion at equivalent time points, which may translate into improved functional capacity.

Exercise in the heat: challenges and opportunities

Exercise in the heat poses a formidable challenge to the body's ability to control its internal environment due to the high rates of metabolic heat production and heat gain by physical transfer from the environment. In an attempt to restrict the rise in core temperature, an increased rate of sweat secretion onto the skin is invoked. This may limit the rise in core temperature, and can prolong the time before a limiting temperature is attained, but it does so at the cost of a loss of body water and electrolytes. The effects of the diminished blood volume are offset to some extent by cardiovascular adaptations, including an increased heart rate and an increased peripheral resistance, but these are insufficient to maintain functional capacity when blood volume is reduced. Prior dehydration will impair performance in both prolonged exercise and short-term high-intensity exercise. Athletes living and training in the heat may experience chronic hypohydration due to inadequate replacement of fluid losses. The negative consequences of exercise in the heat are attenuated to some extent by a period of adaptation, and by the ingestion of water or other appropriate fluids. Optimum fluid replacement strategies will depend on the exercise task, the environmental conditions and the individual physiological characteristics of the athlete. Manipulation of pre-exercise body temperature can also influence exercise performance and may be a strategy that can be used by athletes competing in stressful environments.

Complement is required for the induction of endotoxic fever in guinea pigs and mice

(1) Cobra venom factor (CVF)-induced hypocomplementemia dose-dependently attenuates the febrile responses of guinea pigs and mice to intraperitoneally (ip) but not to intravenously (iv) injected endotoxic bacterial lipopolysaccharide (LPS). (2) Iv but not ip LPS causes fever in complement component 3 (C3) gene-ablated mice, but neither iv nor ip LPS evokes a body core temperature ( T c) rise when WT and these mice's C5a receptors type 1 are blocked. C5 knockout mice also do not develop fever following either iv or ip LPS. C5a thus appears to be a critical mediator of LPS fever. (3) C5 knockouts develop fever in response to intracerebroventricularly (icv) injected LPS or prostaglandin (PG)E 2; the site of action of C5a is therefore peripheral rather than central. (4) The initiation of the febrile responses to both iv and ip LPS is temporally correlated with the appearance of LPS in the liver's Kupffer cells (Kc). (5) PGE 2 is released by liver in immediate response to the injection of CVF into the portal vein of anesthetized guinea pigs; its level rises quickly to its maximum. LPS injected similarly also evokes a quick release of PGE 2 from the liver; it, however, is prevented by prior hypocomplementation. (6) Neither LPS nor IL-1 β induces PGE 2 release from Kc in vitro within the first hour after treatment, but serum C and C plus LPS or IL-1 β very quickly trigger PGE 2 increases of similar magnitudes, catalyzed non-differentially by cyclooxygenase (COX)-1 and COX-2. Kc would thus appear to be the principal site of action of C5a, inducing the release of PGE 2. (7) PGE 2 is detectable in the plasma of conscious guinea pigs in temporal correlation with the onset of the T c rise following ip LPS; cytokines appear significantly later. (8) Taken together, these results indicate that LPS-activated C, rather than LPS or IL-1 β by itself, triggers PGE 2 release by Kc. This PGE 2 could be the factor that stimulates vagal afferents, thereby providing the signal to the brain that mediates the febrile response.

No emotional fever in toads

Four Bufo marinus toads and one Bombina bombina toad were placed individually along a temperature gradient where they could regulate their body temperature through behavioral means. When injected intraperitoneally with killed Pseudomonas aeruginosa bacteria, the toads sought heat and raised their body core temperature. Gentle handling by the experimenter, however, was not followed by heat-seeking behavior and rising core temperature. These findings confirm the existence of behavioral fever, but not emotional fever, in the species studied.

Cytokine induction during exertional hyperthermia is abolished by core temperature clamping: neuroendocrine regulatory mechanisms

The immunomodulatory effects of physiological temperature change remain poorly understood and inter-relationships between changes in core temperature, stress hormones and cytokines during exertional hyperthermia are not well established. This experimental study was designed to examine how cytokine (tumour necrosis factor (TNF)-α, interleukin (IL)-6, IL-12 and IL-1ra (receptor antagonist)) and hormone (epinephrine (Epi), norepinephrine (NE), growth hormone (GH) and cortisol (CORT)) responses are modified when the exercise-induced rise in core temperature is attenuated or exacerbated by immersion in a water bath. Ten men ((mean ± SD) age: 26.9 ± 5.7 years; height 1.75 ± 0.07 m; body mass 76.0 ± 10.9 kg; O2 peak: 48.0 ± 12.4 mL kg−1 min−1) completed two 40-min cycle ergometer exercise trials at 65% O2 peak while immersed to mid-chest. Rectal temperature (Tre) peaked at 39.1 ± 0.03 and 37.5 ± 0.13°C during the hot (39°C) and cold (18°C) conditions, respectively. Blood samples were collected before, during (20- and 40-min) and after (30- and 120-min) exercise. Increases in circulating NE (>350%), Epi (>500%), GH (>900%), IL-12 (>150%) and TNF-α (>90%) were greatest after 40-min exercise in the heat. Substantial elevations of CORT (80%), IL-1ra (150%) and IL-6 (>400%) did not occur until after exercise was complete. Core temperature clamping decreased the rise in circulating stress hormone concentrations and abolished increases in plasma cytokine concentrations. These findings suggest that exercise-associated elevations of Tre mediate increases of circulating stress hormones, which subsequently contribute to induction of circulating cytokine release.

Efficacy of Aluminum Weave Jackets in Reducing Thermal Load During High-Intensity Intermittent Exercise

2131 Limiting the rise in core temperature during exercise can have important effects on the health, safety and work/athletic performance of individuals. Aluminum weave materials have been shown to reflect 50 percent of the sun's radiant heat when used as a covering. A high-intensity short duration protocol was chosen to approximate conditions that might be observed in work and athletic situations. PURPOSE: The purpose of this study was to determine the efficacy of aluminum weave jackets in reducing thermal load during high-intensity intermittent outdoor exercise. METHODS: Eight physically active 19–30 year old males were recruited to participate in this study. Each participant, wearing shorts and a short-sleeve shirt, performed two separate trials, one with an aluminum weave jacket (J) and one without (NJ). Each trial consisted of ten repetitions of 100-meter performed in a 20-meter shuttle format at a speed of 4 meters/second. Each repetition was interspersed with 75 seconds of rest (work:rest, 1:3). During each trial, core temperature (T c), Heart Rate (HR), Thermal Sensation (TS), and Rating of Perceived Exertion (RPE) were measured. RESULTS: All trials demonstrated a rise in mean Tc (0.87°C) and increased mean HR (98 bpm) above rest. Final work values for TS (5.8) and RPE (14.8) were also significantly higher than rest. There was no significant difference between J and NJ trials in measures of Tc, HR, TS and RPE. CONCLUSIONS: Aluminum weave jackets did not show a significant improvement in reducing thermal load during high-intensity intermittent exercise. Supported by Xton, Inc.

Efficacy of Aluminum Weave Jackets in Reducing Thermal Load During High-Intensity Intermittent Exercise

2131 Limiting the rise in core temperature during exercise can have important effects on the health, safety and work/athletic performance of individuals. Aluminum weave materials have been shown to reflect 50 percent of the sun's radiant heat when used as a covering. A high-intensity short duration protocol was chosen to approximate conditions that might be observed in work and athletic situations. PURPOSE: The purpose of this study was to determine the efficacy of aluminum weave jackets in reducing thermal load during high-intensity intermittent outdoor exercise. METHODS: Eight physically active 19–30 year old males were recruited to participate in this study. Each participant, wearing shorts and a short-sleeve shirt, performed two separate trials, one with an aluminum weave jacket (J) and one without (NJ). Each trial consisted of ten repetitions of 100-meter performed in a 20-meter shuttle format at a speed of 4 meters/second. Each repetition was interspersed with 75 seconds of rest (work:rest, 1:3). During each trial, core temperature (T c), Heart Rate (HR), Thermal Sensation (TS), and Rating of Perceived Exertion (RPE) were measured. RESULTS: All trials demonstrated a rise in mean Tc (0.87°C) and increased mean HR (98 bpm) above rest. Final work values for TS (5.8) and RPE (14.8) were also significantly higher than rest. There was no significant difference between J and NJ trials in measures of Tc, HR, TS and RPE. CONCLUSIONS: Aluminum weave jackets did not show a significant improvement in reducing thermal load during high-intensity intermittent exercise. Supported by Xton, Inc.

CCK-8 and PGE 1: central effects on circadian body temperature and activity rhythms in rats

Cholecystokinin-octapeptide (CCK-8) has been shown to possess an acute thermogenic and hyperthermic action when given intracerebroventricularly in slightly restrained rats. To substantiate the febrile nature of that hyperthermia freely moving animals should be used and together with body core temperature, at least one behavioral parameter, such as general activity, should also be recorded. In the present studies, Wistar rats ( N=34) exposed to thermoneutral (26–28 °C) or cold (4 °C) ambient temperature and to a 12:12-h light/darkness schedule were infused intracerebroventricularly with CCK-8 or prostaglandin E 1 (PGE 1) for several days using ALZET minipump and changes in body core temperature and general activity were recorded by biotelemetry (Minimitter). In rats exposed to a thermoneutral ambient temperature, low doses of CCK-8 induced slight but significant rises of day minima of circadian body temperature rhythm (CBTR) and with a high dose (1 μg/h) of the peptide—infused either at thermoneutrality or during cold exposure—an increase of acrometron could also be recorded. All of these changes were observed only during the first 2–4 days of 7-day-long infusions. Intracerebroventricular infusion of PGE 1 administered at thermoneutrality in a dose of 1 μg/h for 7 days induced a marked rise in body core temperature with a disappearance of CBTR in some rats for 2–3 days or with rises of day minima/acrometron in others. General activity—running parallel with CBTR in periods without infusions—tended to be decreased when core temperature rose during the first couple of days of intracerebroventricular infusion of higher doses of CCK-8 or of PGE 1. The decreased general activity—one component of sickness behavior—together with an increased body core temperature found in the present study, supports the view that they are components of a genuine fever induced by the central effect of the two mediators used.

A Simple Method for Calculating Core Temperature Rise in Power Transformers

This paper presents a new method for calculating core temperature rise in large power transformers. A general formulation of the problem is made using the electrical analogy. This formulation extends to the L- and T-joints. An expression for the thermal resistance of the core material is found using analytical methods. A comparison of the results of the new method with measured values on two power transformers is presented.

Preferred illuminance self-selected by women under the influence of face cooling

The aim of the study was to investigate the illuminance selected in the morning by subjects whose face was cooled and whose tympanic temperature has been lowered by 0.15–0.25 °C. The hypothesis tested was that a difference between the actual core temperature and its set point (load error) will influence the preferred illuminance. Specifically, it was hypothesised that a greater load error would lead to the choice of a higher light intensity because this would suppress the melatonin secretion more effectively and thus accelerate the morning rise of core temperature. Seven females served as participants. They were required to rise in the morning 3 h after their minimum rectal temperature, as judged from measurements of rectal temperature made during sleep. The subjects sat 1.5 m away from a lighting box and every 15 min were instructed to choose the level of illuminance (light intensity) they preferred by manipulating a lever in the control box. This procedure was performed twice, in the face-cooling and no-face-cooling condition. The major finding was that a higher light intensity was preferred when the face was cooled down by 0.15–0.25 °C, suggesting that an increased load error between actual core temperature and its set point may play a behavioural role in the selection of preferred illuminance.

Thermoregulation During Mild Exercise at Different Circadian Times

Eight healthy subjects exercised at 90 watts on a cycle ergometer on four occasions, at times close to the minimum, maximum rate of rise, maximum, and maximum rate of fall of their resting core temperature. The duration of exercise was determined by the time taken for the core (rectal) temperature to reach an equilibrium value. Forearm skin blood flow and temperature were measured regularly during the exercise, as were heart rate and ratings of perceived exertion. Sweat loss was calculated by weighing the subjects nude before and after the exercise. The rise of heart rate was not significantly different at the four times of exercise, though the rating of perceived exertion was greatest at 05:00 h. Resting core temperatures showed a significant circadian rhythm at rest (the timing of which confirmed that exercise was being performed at the required times), but the amplitude of this rhythm was decreased significantly by the exercise. The initial rate of rise of core temperature, and the total rise from the resting to the equilibrium value, were both inversely proportional to resting temperature. The time-course of the rise was accurately described by a negative-exponential model, but this model gave no evidence that the kinetics of the equilibration process depended upon the time of day. The thermoregulatory responses to the rise in core temperature—the amount of total sweat loss and rises in forearm skin blood flow and temperature—differed according to the time of exercise. In general, the responses were significantly greater at 17:00 h compared with 05:00 h, and at 23:00 h compared with 11:00 h. The results accord with predictions made on the basis of previous work by us in which core temperature rhythms have been separated into components due to the endogenous body clock and due to the direct effects of spontaneous activity. The results are discussed in terms of the ecological implications of the differing capabilities of humans to deal with heat loads produced by spontaneous activity or mild exercise at different phases of the circadian rhythm of resting core temperature.

Effect of antiperspirants on whole body sweat rate and thermoregulation

It is well established that the evaporation of sweat from the human body surface is the main mechanism by which heat balance is maintained following a rise in body core temperature. Since the introduction of the first brand name antiperspirant in the United States during the early 1900s, antiperspirant products designed to control underarm wetness have grown to represent one of the largest cosmetic categories in most global markets. However, although axillary sweating only constitutes less than 1% of whole body sweat rate, consumers, particularly in hot countries, have begun to articulate the concern that antiperspirants may interfere with the body's natural cooling process. To investigate this, we undertook carefully designed experiments that measured the effects of axillary antiperspirant application on whole body sweat rate and body core temperature, following a regimen of exercise-induced heat stress in a hot environment in human volunteers. Our data show clearly that although antiperspirant prevents sweat production in the axillary area, this does not impact the ability of the body to thermoregulate following a rise in body core temperature. Thus, recent consumer questioning over this aspect of antiperspirant use appears to be unwarranted.

Mice deficient in prostaglandin EP3 receptors do not induce fever but produce psychological stress-induced rise in core temperature

Mice deficient in prostaglandin EP3 receptors do not induce fever but produce psychological stress-induced rise in core temperature

Effects of sevoflurane and isoflurane on the efficacy of rewarming from hypothermic cardiopulmonary bypass

Effects of sevoflurane and isoflurane on the efficacy of rewarming from hypothermic cardiopulmonary bypass

FOOT COOLING DURING EXERCISE ATTENUATES THE RISE IN TYMPANIC TEMPERATURE IN INDIVIDUALS WITH SPINAL CORD INJURY

Individuals with spinal cord injury (SCI) are encouraged to exercise to promote overall health and well-being. However, loss of autonomic nervous system function below the site of the lesion can compromise thermoregulatory capacity. We tested a new cooling device (AV Acore Inc) that focuses on the heat exchanging anastomoses in the feet to directly manipulate core temperature with the intent of increasing exercise capacity. PURPOSE To test the hypotheses that 1) exercise in a heated environment (mean±SEM, 31.9 ± 0.1° C) would increase core temperature more in SCI than able-bodied (AB) subjects, and 2) the foot cooling device would attenuate the rise in core temperature during exercise in both groups. METHODS Six SCI subjects with lesions between C5 and T5 and six AB controls were matched as closely as possible for age (43 ± 4 vs 49.9 ± 3 ns), arm-crank VO2max (14.4 ± 2.9 vs 18.5 ± 1.2 ml/kg•min ns) and body fat percentage (22.1 ± 3.0 vs 17.8 ± 2.1 ns). Subjects arm-cranked for 45 min at approximately 66 ± 0.5% VO2max and recovered for 30 min on two separate occasions with either foot cooling device (FC) or no foot cooling (NC) in randomized order. RESULTS Within the SCI group, tympanic temperature (Ty) was elevated above baseline for both trials (P < 0.001), but was higher in the NC vs. FC trial (P < 0.001) from min 15 of exercise throughout recovery. For SCI, peak increases in Ty were 1.5 ± 0.2° C and 1.0 ± 0.2° C for NC and FC, respectively. There were no within- or between-trial differences for the AB group. Between the SCI and AB groups, Ty was higher in the SCI FC vs AB FC (P < 0.001) and SCI NC vs AB NC (P < 0.001) from min 25 of exercise throughout recovery. CONCLUSION Foot cooling with the AV Acore device during exercise in the heat attenuated the rise in Ty in SCI individuals, but did not impact AB Ty. Therefore, foot cooling may provide an effective way to manipulate core temperature in individuals with SCI especially during exercise. Supported by Dept of Veterans Affairs.

The spleen modulates the febrile response of guinea pigs to LPS.

The febrile responses of splenectomized (Splex) or sham-operated (Sham) guinea pigs challenged intravenously or intraperitoneally with lipopolysaccharide (LPS) 7 and 30 days after surgery were evaluated. FITC-LPS uptake by Kupffer cells (KC) was additionally assessed 15, 30, and 60 min after injection. LPS at 0.05 microg/kg iv did not evoke fever in Sham animals but caused a 1.2 degrees C core temperature (T(c)) rise in the Splex animals. LPS at 2 microg/kg iv induced a 1.8 degrees C greater T(c) rise of the Splex animals than of their controls. LPS at 2 and 8 microg/kg ip 7 days postsurgery induced 1.4 and 1.8 degrees C higher fevers, respectively, in the Splex than Sham animals. LPS at 2 and 8 microg/kg ip 30 days postsurgery also increased the febrile responses of the asplenic animals by 1.6 and 1.8 degrees C, respectively. FITC-LPS at 7 days was detected in the controls within KC 15 min after its administration; the label density was reduced at 30 min and almost 0 at 60 min. In the Splex group, in contrast, the labeling was significantly denser and remained unchanged through all three time points; this effect was still present 30 days after surgery. Similar results were obtained at 60 min after FITC-LPS intraperitoneal injection. Gadolinium chloride pretreatment (-3 days) of the Splex group significantly reduced both their febrile responses to LPS (8 microg/kg ip) and their KC uptake of FITC-LPS 7 days postsurgery. Thus splenectomy increases the magnitude of the febrile response of guinea pigs and the uptake of systemically administered LPS.

Increased thermoregulatory responsiveness in cold adapted but not in hyperthyroid hypermetabolic rats.

Cold-adapted (CA) rats, unlike non-adapted (NA) ones, give exaggerated metabolic response to acute cold exposure, with paradoxical "overshoot" core temperature (Tc) rise in the cold, and they also give enhanced hyperthermia to central injection of prostaglandin E1 (PGE1). The adaptation-dependent differences might be explained either by the high thermogenic capacity of peripheral tissues in CA rats or by differences in the central processing of regulatory signals. If high tissue metabolism sufficiently explains the extreme responses of CA animals, other hypermetabolic states (with high resting metabolic rate, RMR), e.g. hyperthyroidism, should also be accompanied by enhanced reactions. In the present study thermoregulatory responses to acute cold exposure or to PGE1 were compared in hypermetabolic CA, similarly hypermetabolic thyroxine-treated (T4) and control non-hypermetabolic NA rats (mean RMR = 8.12, 8.47 and 6.03 W kg(-1), respectively). Cold exposure was followed by paradoxical core temperature (Tc) rise of 0.5 to 0.7 degrees C only in CA rats, but by Tc fall (0.8 to 2.1 degrees C) in NA and T4 animals. Identical central stimuli (PGE1) induced larger elevations of Tc and metabolic rate in CA rats than in similarly hypermetabolic T4 or in non-hypermetabolic NA animals (mean Tc rise of 1.9 degrees C in CA vs. 0.9 degrees C in T4 and 1.0 degrees C in NA rats). Vasodilatation thresholds were also similar in NA and T4, but lowered in CA animals. A hypermetabolic status, per se, does not seem to explain the enhanced thermoregulatory responsiveness of CA animals, adaptation-induced central regulatory changes may be more important for the "overshoot" phenomenon.

SURFACE WETTING AND ITS OPTIMIZATION TO COOL BROILER CHICKENS

Surface wetting to cool broiler chickens (Ross . Ross male, 46 .3 d, 2.8 . 0.1 kg) was investigated under 18acute thermal conditions formed by 3 . 2 . 3 factorial combinations of drybulb temperature (tdb) of 35.C, 38.C, and 41.C;dewpoint temperature (tdp) of 19.4.C and 26.1.C; and air velocity (V) of 0.2, 0.7, and 1.2 m s1. The synergistic effects oftdb and tdp were expressed in terms of vapor pressure deficit of the air (VPDair, kPa). Surface temperature of the cooled birdswas 1.9.C to 2.5.C lower than that of their control counterparts. Core body temperature (tb) rise above the normal level forthe cooled birds was 1.2.C, 1.6.C, and 1.7.C lower than that for the control birds at 35.C, 38.C, and 41.C, respectively.Increasing V tended to narrow the difference in tb between the cooled and the control broilers, 2.0.C, 1.4.C, and 1.2.C forV of 0.2, 0.7, and 1.2 m s1, respectively. Increasing tdp from 19.4.C to 26.1.C produced only 0.2.C overall difference in tb.Results of this study demonstrate that surface wetting coupled with good air movement, as in the case of tunnel ventilation,is effective in relieving heat stress of the birds even under relatively humid conditions. The cooling water needs, expressedas spray interval at a nominal spray dosage of 22 mL bird1 (SI22, min) and evaporation rate (ER, mL/min kg0.67), wereoptimized by relating the SI22 or ER to the thermal conditions: SI22 = 70.50 27.14 V 4.84VPDair, and ER = 0.0471 +0.1700 V + 0.0297VPDair.

Role of Prostaglandin E2 and Indomethacin in the Febrile Response of Pigeons

Intravenous (i.v.) injection of 10 microg/kg Escherichia coli lipopolysaccharide (LPS), applied at 13:00, evoked in pigeons a biphasic rise of core temperature (T(core)), so that LPS induced with a latency of 30 min first a decrease of T(core), and 90 min after LPS, T(core) increased, obtaining maximum values from 18:00 to 20:00. Prostaglandins have been considered to be importantly involved in fevers in mammals. To investigate an involvement of prostaglandins in the cyclic variations of T(core) in birds, pigeons were injected i.v. with either 10 mg/kg indomethacin (INDO) or 100 mg/kg aspirin, or they were treated with intracerebroventricular (i.c.v.) injections of 100 microg/kg INDO at various times before or after LPS. When INDO or aspirin was i.v. injected 30 or 15 min before LPS, it diminished the initial decrease of T(core) by more than 50%, whereas the i.v. injection of these drugs 2 and 4 h after LPS did not affect the febrile rise of T(core). i.c.v. injections of INDO given either before or after LPS neither influenced the initial drop of T(core) nor the following febrile hyperthermia. Both the i.v. injection of 1 mg/kg prostaglandin E(2) (PGE(2)) and the i.c.v. injection of 1 microg/kg PGE(2) lowered T(core). Our observations suggest that prostaglandins are not involved in the febrile elevation of T(core) in pigeons, but appear to participate in the decrease of T(core), which shortly follows the i.v. injection of LPS. This initial drop of T(core) following LPS may be caused by a peripheral action of prostaglandins because it was not influenced by the i.c.v. injection of indomethacin.