Respiratory Evaporative Heat Loss Research Articles

Reply to Kenney.

Reply to Kenney.

Ultradian oscillations in brain temperature in sheep: implications for thermoregulatory control?

We compared body temperature patterns and selective brain cooling (SBC) in eight adult female sheep in an indoor (22-25°C) and outdoor (mean ~ 21°C) environment, by measuring brain, carotid arterial, and jugular venous blood temperatures at 5-min intervals using implanted data loggers. To investigate whether ultradian oscillations in brain temperature had thermoregulatory consequences for the sheep, we determined the cranial arterio-venous (AV) temperature difference as an indicator of respiratory evaporative heat loss (REHL). The 24-h pattern of SBC was similar in both environments, despite carotid blood temperature fluctuating 0.4°C more outdoors compared to indoors. The sheep employed SBC more often during the night than during the day, but SBC was abolished at intervals of 1-3h throughout the 24-h period. The suppression of SBC appeared to be associated with events that increased sympathetic nervous system activity, including shifts between stages of sleep. Short-term changes (over 5-min) in brain temperature were positively correlated with changes in the AV temperature difference 5min later, and negatively correlated with changes in carotid temperature 10min later. These data support the idea that increases in brain temperature modulate thermoregulation by increasing REHL, which leads to a decrease in carotid blood temperature. Ultradian oscillations in core temperature of sheep, therefore, appear to arise as a consequence of frequent brain temperature changes invoked by non-thermal inputs, in animals housed both in indoor and outdoor environments.

Bio-thermal responses and heat balance of a hair coat sheep breed raised under an equatorial semi-arid environment.

Long-term assessments of bio-thermal responses in a hair coat sheep breed were performed to investigate the effect of the thermal environment on their physiological performance and thermal balance. Twelve healthy non-lactating Morada Nova ewes (3 ± 1.2 years old, body mass 32.7 ± 3.7 kg) were assigned in two 12 × 12 latin square designs (from 07:00 to 19:00 h and from 19:00 to 07:00 h, respectively) for assessments of their bio-thermal responses during 24 consecutive days. There was a monophasic pattern in the ambient temperature (TA), which ranged between 21 and 38 °C, thereby exposing the ewes to different levels of surrounding TA over the day and influencing several of their bio-thermal responses (P = 0.0001). Their body temperatures (i.e., rectal, skin, and hair coat surface temperatures) gradually increased (P = 0.0001) from 04:00 h. The mean peak for rectal temperature (39.3 °C) was recorded at 19:00 h, while for skin and hair coat surface temperatures it occurred at 13:00 and 14:00 h, respectively. The sensible heat loss by long wave radiation and surface convection exceeded the metabolism of ewes when the TA was below 24 °C, which usually occurred between 24:00 and 06:00 h. During exposure to higher ambient temperatures, the sheep increased respiratory evaporative heat loss, without panting. In conclusion, the sheep regulated rectal temperature within a relatively narrow range of 1.4 °C over 24 h, and appear to be well adapted to coping with heat. Minimum 24 h body temperature was correlated with minimum TA, indicating that heat conservation strategies are likely to be important for Morada Nova sheep in a tropical biotype at night, when rates of sensible heat loss exceed the heat generated by metabolism.

Sensitivity, Impact and Consequences of Changes in Respiratory Rate During Thermoregulation in Livestock – A Review

Abstract This review discusses the thermal conservative and heat dissipating roles of one of the most sensitive thermoregulatory variables (respiratory rate) with the aim of enhancing its application in evaluating both cold and heat adaptation. During cold exposure, livestock enhance the economy of body heat through reduction in respiratory rate with the extent of reduction being greater and commencing at relatively higher ambient temperature in poorly adapted phenotypes. This is accompanied by an increase in tidal volume and alveolar oxygen uptake, but a decrease in partial pressure of oxygen. On the other hand, heat stress induces increase in respiratory rate to enhance evaporative heat loss with the magnitude of such increase being greater and commencing at relatively lower ambient temperature in phenotypes that are poorly-adapted to heat. This is accompanied by a decrease in tidal volume and the development of hypocapnia. The increase in respiratory rate is observed to be greater, moderate and lesser in livestock that are mainly (pigs, rabbits and poultry), moderately (sheep, goats and Bos taurus) and less (Zebu cattle) dependent on respiratory evaporative heat loss, respectively. The changes during chronic heat stress may cause acid-base crisis in all livestock, in addition to reduction in eggshell quality in birds; due to marked decrease in partial pressure of carbon dioxide and a compensatory increase in elimination of bicarbonate. Within and between breed variations in sensitivity of respiratory rhythm to both cold and heat stress has shown high applicability in identifying phenotypes that are more susceptible to thermal stress; with some cellular and metabolic changes occurring to protect the animal from the consequences of hypo- or hyper-thermia. The information in this review may provide basis for identification of genes that support or suppress thermoregulation and may also be of great use in animal breeding, genomics and selective thermal stress mitigation to provide maximum protection and comfort to poorly-adapted phenotypes.

Avian thermoregulation in the heat: evaporative cooling in five Australian passerines reveals within-order biogeographic variation in heat tolerance.

Evaporative heat loss pathways vary among avian orders, but the extent to which evaporative cooling capacity and heat tolerance vary within orders remains unclear. We quantified the upper limits to thermoregulation under extremely hot conditions in five Australian passerines: yellow-plumed honeyeater (Lichenostomus ornatus; ∼17 g), spiny-cheeked honeyeater (Acanthagenys rufogularis; ∼42 g), chestnut-crowned babbler (Pomatostomus ruficeps; ∼52 g), grey butcherbird (Cracticus torquatus; ∼86 g) and apostlebird (Struthidea cinerea; ∼118 g). At air temperatures (Ta) exceeding body temperature (Tb), all five species showed increases in Tb to maximum values around 44-45°C, accompanied by rapid increases in resting metabolic rate above clearly defined upper critical limits of thermoneutrality and increases in evaporative water loss (EWL) to levels equivalent to 670-860% of baseline rates at thermoneutral Ta Maximum cooling capacity, quantified as the fraction of metabolic heat production dissipated evaporatively, ranged from 1.20 to 2.17, consistent with the known range for passerines, and well below the corresponding ranges for columbids and caprimulgids. Heat tolerance limit (HTL, the maximum Ta tolerated) scaled positively with body mass, varying from 46°C in yellow-plumed honeyeaters to 52°C in a single apostlebird, but was lower than that of three southern African ploceid passerines investigated previously. We argue this difference is functionally linked to a smaller scope for increases in EWL above baseline levels. Our data reiterate the reliance of passerines in general on respiratory evaporative heat loss via panting, but also reveal substantial within-order variation in heat tolerance and evaporative cooling capacity.

Milk yield in Holstein cows and physiological responses in hot environment

This study is aimed to evaluate the physiological responses and the production of milk cows of the Holstein breed, pure, in the dry and rainy seasons. During the period from March to October rectal temperature (TR), respiratory rate (FR) and milk production (PL) were taken at 7 am and at 3 pm twice a week, in eleven cows. At the same time, in these cows there were also recorded temperatures of air and black globe, humidity and it was calculated the Globe and Humidity Temperature Index (ITGU). Statistical analyzes were performed by the method of least squares and this revealed significant effects of the animal, also the year of the period and month collection period within the year on the variables recorded, with higher TR and FR during the rainy season, when the PL was higher. There was a significant time interaction and animals just for the PL and the interaction time of collection and time for PL and TR. The effects of ITGU in the shade and the sun were different only concerning the FR. Milk production was extremely low in all periods of the year and in the dry season, in the afternoon, there was a higher body heat, and in the rainy season the use of the mechanisms of respiratory evaporative heat loss was intensified.

Regulation of brain temperature in winter-acclimatized reindeer under heat stress

Reindeer (Rangifer tarandus) are protected against the Arctic winter cold by thick fur of prime insulating capacity and hence have few avenues of heat loss during work. We have investigated how these animals regulate brain temperature under heavy heat loads. Animals were instrumented for measurements of blood flow, tissue temperatures and respiratory frequency (f) under full anaesthesia, whereas measurements were also made in fully conscious animals while in a climatic chamber or running on a treadmill. At rest, brain temperature (T(brain)) rose from 38.5±0.1°C at 10°C to 39.5±0.2°C at 50°C, while f increased from ×7 to ×250 breaths min(-1), with a change to open-mouth panting (OMP) at T(brain) 39.0±0.1°C, and carotid and sublingual arterial flows increased by 160% and 500%, respectively. OMP caused jugular venous and carotid arterial temperatures to drop, presumably owing to a much increased respiratory evaporative heat loss. Angular oculi vein (AOV) flow was negligible until T(brain) reached 38.9±0.1°C, but it increased to 0.81 ml min(-1) kg(-1) at T(brain) 39.2±0.2°C. Bilateral occlusion of both AOVs induced OMP and a rise in T(brain) and f at T(brain) >38.8°C. We propose that reindeer regulate body and, particularly, brain temperature under heavy heat loads by a combination of panting, at first through the nose, but later, when the heat load and the minute volume requirements increase due to exercise, primarily through the mouth and that they eventually resort to selective brain cooling.

The effects of theophylline and caffeine on thermoregulatory functions of rats at different ambient temperatures.

Both systemic and central administration of theophylline and caffeine produced a dose-dependent rise in rectal temperature at ambient temperatures of 8, 22 and 30 degrees C. The hyperthermia in response to either xanthine was brought about by an increase in metabolic heat production. In addition, their administration produced behavioral excitation, cutaneous vasodilation (as estimated by an increase in the foot and tail skin temperatures) and diuresis. There was no change in respiratory evaporative heat loss. Probably, the hyperthermia induced by the two drugs was due to behavioral excitation leading to an increased metabolism at the ambient temperatures studied. Furthermore, either destruction of central catecholaminergic nerve fibres (with 6-hydroxydopamine) or blockade of alpha-adrenergic and dopaminergic (with phentolamine and haloperidol) receptors antagonized the xanthine-induced hyperthermia. The data suggest that these xanthines elicit a central activation of both adrenergic and dopaminergic receptors via release of endogenous catecholamines that leads to behavioral excitation and hyperthermia in rats.

The cranial arterio-venous temperature difference is related to respiratory evaporative heat loss in a panting species, the sheep (Ovis aries)

Panting is a mechanism that increases respiratory evaporative heat loss (REHL) under heat load. Because REHL uses body water, it is physiologically and ecologically relevant to know under what conditions free-ranging animals use panting. We investigated whether the cranial arterio-venous temperature difference could provide information about REHL. We exposed sheep to environments varying in ambient dry bulb temperatures (Env 1: ~15°C, Env 2: ~25°C, Env 3: ~40°C, Env 4: ~40°C+infrared radiation) and measured REHL simultaneously with carotid arterial (T (car)) and jugular venous (T (jug)) blood temperatures, as well as brain (T (brain)) and rectal (T (rec)) temperatures. REHL increased significantly with ambient temperature, from 18.4±4.5W at Env 1 to 79.5±12.6W at Env 4 (P<10(-6)). While there was no effect of environment on T (car) (P=0.7) or T (jug) (P=0.09), the difference between them (T (a-v)=T (car)-T (jug)) increased from Env 1 to Env 2 (P=0.04) and from Env 3 to Env 4 (P=0.008). T (a-v) reached a maximum of 0.7±0.2°C at Env 4 and was positively correlated with REHL across environments (r (2)=0.78, F=34.7, P<10(-3)). Calculated cranial blood flow changed only from Env 2 to Env 3 (P=0.002). The increase in REHL maintained homeothermy when dry heat loss decreased. While REHL could increase without generating an increase in T (a-v), any increase in T (a-v) was always associated with an increase in REHL. We conclude that the cranial T (a-v) provides useful information about REHL in panting animals.

Predicted limits for evaporative cooling in heat stress relief of cattle in warm conditions

Evaporative cooling of ambient air (EC) is a main path for heat stress relief in cattle kept in the shade of semi-confining structures. Evaporative cooling is particularly efficient in hot dry climates. We examined the potential of EC for heat stress relief in cattle in moderately warm and humid climates. The feasibility was examined by the reduction in ambient temperature (T(ac)) produced by EC as a function of ambient temperature (T(a)) and humidity (RH(a)). A data set (n = 139) of temperature and relative humidity (RH) produced by EC over a range of air temperature (25 to 50 degrees C) and humidity (10 to 70% RH) was analyzed by polynomial second order regressions. The analyses produced equations for the relations between ambient air temperature and ambient humidity and between respective conditions in air cooled by EC (T(c), RH(c)). Linear regressions were computed for a narrower temperature range (30 to 40 degrees C). In all equations, R(2) were >0.94 and regression terms were statistically significant. The T(ac) obtained by EC diminished by 0.3 degrees C per degrees C rise in T(a), indicating a reduced efficiency of EC with rising T(a). The T(ac) obtained by EC also was markedly reduced by rising ambient humidity and increased by RH(c). An attempt to sustain T(ac) at greater RH(a) by allowing a rise in RH(c) would only restore 2/3 of the reduction in T(ac) because the coefficient for the RH(a) effect on T(ac) is 1.5 larger than that of RH(c). The T(ac) attained by EC partially depends on the humidity in the cooled environment. Elevated RH(c) may impede animal skin and respiratory evaporative heat loss and lead to moisture accumulation in bedding. If the upper desired limit for RH(c) is 70%, at RH(a) smaller than 45% (typical for hot-dry environments) the T(ac) is larger than 7.5 degrees C, at RH(a) greater than 55% T(ac) is reduced to less than 5 degrees C, and at RH(a) of 57.5 to 60% T(ac) is about 2.5 degrees C. Coupling EC with forced air movement when T(ac) is small may partially assist in alleviation of heat stress by enhancing the smaller convective heat loss at ambient temperatures above 30 degrees C. These indicate a limited role for EC in relief of heat stress in moderately warm and humid conditions when RH(a) is greater than 50 to 55%. Forced evaporation of water from the surface of the animal by sequential hair coat wetting coupled with forced air movement is an alternative little affected by ambient humidity.

The effect of fleece on core and rumen temperature in sheep

Temperature loggers were implanted to record core body temperature ( T core) and rumen temperature ( T rumen) in sheep. The relationship between T core and T rumen was compared for fleeced and shorn Merino sheep over a range of environmental temperatures and during stressors involved with shearing. Fleeced sheep maintained higher T core and T rumen than shorn sheep in all environmental conditions tested (from thermoneutral up to 33 °C and 55% relative humidity). Shearing of the fleeced sheep resulted in those sheep having a lower T core when exposed to hot conditions, compared to the previously shorn sheep. Respiratory rates of fleeced sheep followed similar patterns and were higher than shorn sheep under all environmental conditions. After the fleeced sheep were shorn, their respiratory rates decreased to rates similar to the previously shorn sheep when under heat load, suggesting heat loss other than respiratory evaporative heat loss was augmented.

Thermoregulation in pronghorn antelope (Antilocapra americanaOrd) in the summer

We have used thermistor/data logger assemblies to measure temperatures in the brain, carotid artery, jugular vein and abdominal cavity, and subcutaneously, in five pronghorn antelope over a summer in Wyoming. Globe and air temperature varied by up to approximately 50 degrees C daily during the summer and maximum solar radiation was approximately 900 W m(-2). Brain temperature (38.9+/-0.3 degrees C) was consistently approximately 0.2-0.5 degrees C higher than carotid blood temperature (38.6+/-0.3 degrees C), which was the same as abdominal temperature (38.8+/-0.4 degrees C). Jugular blood temperature (38.0+/-0.4 degrees C) varied, probably because of changes in Respiratory Evaporative Heat Loss (REHL), and was lower than other temperatures. Subcutaneous temperature (38.3+/-0.6 degrees C) varied, probably because of peripheral vasoactivity, but on average was similar to other temperatures. Carotid blood temperature had a circadian/nycthemeral rhythm weakly but significantly (r=0.634) linked to the time of sunrise, of amplitude 0.8+/-0.1 degrees C. There were daily variations of up to 2.3 degrees C in carotid body temperature in individual animals. An average range of carotid blood temperature of 3.1+/-0.4 degrees C over the study period was recorded for the group, which was significantly wider than the average variation in brain temperature (2.3+/-0.6 degrees C). Minimum carotid temperature (36.4+/-0.8 degrees C) was significantly lower than minimum brain temperature (37.7+/-0.5 degrees C), but maximum brain and carotid temperatures were similar. Brain temperature was kept relatively constant by a combination of warming at low carotid temperatures and cooling at high carotid temperatures and so varied less than carotid temperature. This regulation of brain temperature may be the origin of the amplitude of the average variation in carotid temperature found, and may confer a survival advantage.

Mechanisms for the control of respiratory evaporative heat loss in panting animals

Panting is a controlled increase in respiratory frequency accompanied by a decrease in tidal volume, the purpose of which is to increase ventilation of the upper respiratory tract, preserve alveolar ventilation, and thereby elevate evaporative heat loss. The increased energy cost of panting is offset by reducing the metabolism of nonrespiratory muscles. The panting mechanism tends to be important in smaller mammalian species and in larger species is supplemented by sweating. At elevated respiratory frequencies and body temperatures alveolar hyperventilation begins to develop but is accompanied by a decline in the control of carbon dioxide partial pressure in arterial blood, probably through central chemoreceptors. Most heat exchange takes place at the nasal epithelial lining, and venous drainage can be directed to a special network of arteries at the base of the brain whereby countercurrent heat transfer can occur, which results in selective brain cooling. Such a phenomenon has also been suggested in nonpanting species, including humans, and although originally thought to be a mechanism for protecting the thermally vulnerable brain is now considered to be one of the thermoregulatory reflexes whereby respiratory evaporation can be closely controlled in the interests of thermal homeostasis.

Reduction of the Pa CO 2 set point during hyperthermic exercise in the sheep

In animals that rely on the respiratory system for both gas exchange and heat loss, exercise can generate conflict between chemoregulation and thermoregulation. We hypothesized that in panting animals, hypocapnia during hyperthermic exercise reflects a reduction in the arterial CO 2 tension (Pa CO 2 ) set point. To test this hypothesis, five sheep were subjected to tracheal insufflations of CO 2 or air (control) at 3–4 L min −1 in 3 min bouts at 5 min intervals over 31 min of exercise. During exercise, rectal temperature and minute ventilation ( V E) rose continuously while Pa CO 2 fell from 35.4±3.1 to 18.6±2.9 Torr and 34.3±2.4 to 18.7±1.5 Torr in air and CO 2 trials, respectively. Air insufflations did not affect V E or Pa CO 2 . V E increased during CO 2 insufflations via a shift to higher tidal volume and lower frequency. CO 2 insufflations also increased Pa CO 2 , although not above the pre-exercise level. Within 5 min after each CO 2 insufflation, Pa CO 2 had decreased to match that following the equivalent air insufflation. These results are consistent with a reduced Pa CO 2 set point or an increased gain of the Pa CO 2 regulatory system during hyperthermic exercise. Either change in the control of Pa CO 2 could facilitate respiratory evaporative heat loss by mitigating homeostatic conflict.

Giraffe Thermoregulation: a review

The ability to maintain a relatively constant body temperature is central to the survival of mammals. Giraffes are found in relatively hot rather than cold environments, have a body temperature of 38.5 ± 0.5°C, and must have evolved appropriate thermoregulatory mechanisms to maintain this temperature and to survive in their chosen habitats. Their thermoregulation depends on anatomical features and behavioural and physiological mechanisms. To minimize physiological thermoregulation giraffes orientate their bodies to optimize radiant heat gain and to maximize convective heat loss, and seek shade. Their long and slender, “dolicomorphic” shape by increasing body surface area without proportionally increasing their metabolic mass enhances heat loss mechanisms. Their ossicones are well vascularized and may also function as a thermoregulatory organ. The main physiological mechanism for achieving heat loss is evaporation. Giraffe nasal anatomy and their unique respiratory system can combine to cause high respiratory evaporative heat loss and, theoretically, cooling of jugular venous blood. Evaporation of sweat is another heat loss mechanism but has not before been reported to occur in giraffes. We have analysed the anatomy of giraffe skin and show that it contains many active sweat glands, and that the size of these glands is significantly greater under patches than it is elsewhere. Giraffes therefore can and in some circumstances will sweat. When combined with the anatomy of the blood vessels supplying patches these data further support the idea that patches are thermal windows. We conclude that giraffe have evolved an array of thermoregulatory mechanisms, mostly to achieve heat loss, which make them well adapted to hot and arid environments.

Effects of Exposure to High Temperature and Feeding Level on Regional Blood Flow and Oxidative Capacity of Tissues in Piglets

To determine to what extent exposure to high ambient temperature and feeding level affect tissue energy metabolism in piglets, regional blood flow and oxidative capacity of tissues were evaluated in sixteen 21.8 +/- 2.8 kg pigs. At 5 weeks of age, littermates were divided into three groups and acclimated to the treatment for 25 days. One group was reared at 33 degrees C and fed ad libitum (33AL, n = 6) while the other two groups were maintained at 23 degrees C and either pair-fed on the basis of the food consumption of their 33AL littermates (23PF, n = 5), or fed ad libitum (23AL, n = 5). Regional blood flow was determined in conscious pigs by injection of coloured microspheres, which were recovered in different tissues after slaughter. Activities of cytochrome oxidase and cytochrome aa(3) content were measured in tissue homogenates of heart, longissimus dorsi and rhomboideus muscles, liver and small intestine. There was decreased blood flow to internal adipose tissue (42 %) and increased blood flow to peripheral tissues (skin, 44 %) and tissues implicated in respiratory evaporative heat loss (diaphragm, 45 %, lungs, 59 %) at 33 degrees C compared to 23 degrees C, which can be viewed as an effective mechanism for increasing heat loss at high temperature. In addition, the concomitant decrease in blood flow (49 %) and slight reduction of oxidative capacities in both muscles at 33 degrees C might contribute to the reduction in thermogenesis, but these effects were also observed when the feeding level was reduced at thermal neutrality (23PF group). In the viscera (intestine, liver), blood flow was decreased in the two groups on a restricted food intake (about 50 % of 23AL), independently of environmental temperature. The results suggest that most of the mechanisms associated with the reduction in energy expenditure during warm acclimation are related to the adaptive reduction in food intake. Experimental Physiology (2001) 86.1, 83-91.

Ventilatory accommodation of oxygen demand and respiratory water loss in kangaroos from mesic and arid environments, the eastern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus).

We studied ventilation in kangaroos from mesic and arid environments, the eastern grey kangaroo (Macropus giganteus) and the red kangaroo (Macropus rufus), respectively, within the range of ambient temperatures (T(a)) from -5 degrees to 45 degrees C. At thermoneutral temperatures (Ta=25 degrees C), there were no differences between the species in respiratory frequency, tidal volume, total ventilation, or oxygen extraction. The ventilatory patterns of the kangaroos were markedly different from those predicted from the allometric equation derived for placentals. The kangaroos had low respiratory frequencies and higher tidal volumes, even when adjustment was made for their lower basal metabolism. At Ta>25 degrees C, ventilation was increased in the kangaroos to facilitate respiratory water loss, with percent oxygen extraction being markedly lowered. Ventilation was via the nares; the mouth was closed. Differences in ventilation between the two species occurred at higher temperatures, and at 45 degrees C were associated with differences in respiratory evaporative heat loss, with that of M. giganteus being higher. Panting in kangaroos occurred as a graded increase in respiratory frequency, during which tidal volume was lowered. When panting, the desert red kangaroo had larger tidal volumes and lower respiratory frequencies at equivalent T(a) than the eastern grey kangaroo, which generally inhabits mesic forests. The inference made from this pattern is that the red kangaroo has the potential to increase respiratory evaporative heat loss to a greater level.

Effect of locomotor respiratory coupling on respiratory evaporative heat loss in the sheep.

During galloping, many animals display 1:1 coupling of breaths and strides. Locomotor respiratory coupling (LRC) may limit respiratory evaporative heat loss (REHL) by constraining respiratory frequency (f). Five sheep were exercised twice each, according to a five-step protocol: 5 min at the walk, 5 min at the trot (trot1), 10 min at the gallop, 5 min at the trot (trot2), and 5 min at the walk. Rectal temperature (T(re)), stride frequency, f, REHL, and arterial CO(2) tension and pH were measured at each step. Tidal volume (VT) was calculated. LRC was observed only during galloping. The coupling ratio remained at 1:1 while VT increased continuously during galloping, causing REHL to increase from 2.9 +/- 0.2 (SE) W/kg at the end of trot1 to a peak of 5.3 +/- 0.3 W/kg. T(re) rose from 39.0 +/- 0.1 degrees C preexercise to 40.2 +/- 0.2 degrees C at the end of galloping. At the gallop-trot2 transition, VT fell and f rose, despite a continued rise in T(re). Arterial CO(2) tension fell from 36.5 +/- 1.1 Torr preexercise to 31.8 +/- 1.4 Torr by the end of trot1 and then further to 21.5 +/- 1.2 Torr by the end of galloping, resulting in alkalosis. In conclusion, LRC did not prevent increases in REHL in sheep because VT increased. The increased VT caused hypocapnia and presumably elevated the cost of breathing.

Pharmacological properties of traditional medicines. XXV. Effects of ephedrine, amygdalin, glycyrrhizin, gypsum and their combinations on body temperature and body fluid.

Effects of ephedrine, amygdalin, glycyrrhizin, gypsum and their combinations on body temperature and body fluid were studied in rats using the method developed in our previous reports. Ephedrine significantly increased respiratory evaporative water loss and heat loss in response to a marked elevation of body temperature. There was a small but significant increase in body temperature when amygdalin was orally given rats at a dose of 46.32 mg/kg. Glycyrrhizin and gypsum were unable to affect body temperature. However, gypsum was able to prevent the increased action of ephedrine on body temperature, amygdalin exhibited a preventive tendency to it, and glycyrrhizin did not affect it. The results are in good agreement with classical claims of Makyo-kanseki-to and the related crude drugs in traditional medicine. Moreover, a combination of the four components reproduced the effects of Makyo-kanseki-to on body temperature and body fluid. This report suggests that the co-administration of ephedrine and gypsum is physiologically more desirable than ephedrine alone for dry-type asthmatic patients with a fever. Also, it experimentally supports the clinical efficacy of Makyo-kanseki-to.

Selective brain cooling in goats: effects of exercise and dehydration.

1. Measurements of brain and central blood temperature (Tbr and Tbl), metabolic rate (MR) and respiratory evaporative heat loss (REHL) were made in trained goats walking on a treadmill at 4.8 km h-1 at treadmill inclines of 0, 5, 10, 15 and 20% when they were fully hydrated and at 0% when they had been deprived of water for 72 h. 2. In hydrated goats, exercise MR increased progressively with increasing treadmill incline. Both Tbl and Tbr rose during exercise, but Tbl always rose more than Tbr, and selective brain cooling (SBC = Tbl - Tbr) increased linearly with Tbl. Significant linear relationships were also present between REHL and Tbl and between SBC and REHL. Neither the slope of the regression relating SBC to Tbl nor the threshold Tbl for onset of SBC was affected by exercise intensity. Manual occlusion of the angularis oculi veins decreased SBC in a walking goat, while occlusion of the facial veins increased SBC. 3. Dehydrated goats had higher levels of Tbl, Tbr and SBC during exercise, but the relationship between SBC and Tbl was the same in hydrated and dehydrated animals. In dehydrated animals, REHL at a given Tbl was lower and SBC was thus maintained at reduced rates of REHL. 4. It is concluded that SBC is a linear function of body core temperature in exercising goats and REHL appears to be a major factor underlying SBC in exercise. The maintenance of SBC in spite of reduced REHL in dehydrated animals could be a consequence of increased vascular resistance in the facial vein and increased flow of cool nasal venous blood into the cranial cavity.