Evaporative cooling in the rat: Effects of dehydration

1970 ◽  
Vol 48 (1) ◽  
pp. 18-27 ◽  
Author(s):  
Edward M. Stricker ◽  
F. Reed Hainsworth
Keyword(s):  
Heat Stress ◽  
Temperature Regulation ◽  
Water Loss ◽  
Water Conservation ◽  
Evaporative Cooling ◽  
Body Water ◽  
Large Temperature ◽  
Survival Times ◽  
Evaporative Water ◽  
Ambient Temperatures

Previous investigations demonstrated that the water loss of rats associated with increased salivary evaporation during heat stress is derived from both intracellular and intravascular sources. The present studies indicate that sufficient dehydration of either fluid compartment will impair temperature regulation. Salivary excretion from all dehydrated rats was virtually abolished at ambient temperatures below 38–40 °C, but temperature regulation was still possible if a large temperature gradient existed between the animals and the environment. Above these ambient temperatures, where increased evaporation is essential to survival, the rate of evaporative water loss returned to normal. However, body water reservoirs in dehydrated rats were rapidly depleted, salivary evaporation could not be maintained, and survival times were shortened. In contrast, access to drinking water significantly increased thermal tolerance. These results emphasize the importance of adequate body fluid hydration for evaporative cooling through saliva spreading by rats in the heat. In addition, they indicate that allocation of body water for evaporation takes precedence over conflicting demands for water conservation during heat stress.

scholarly journals An experimental evolution study confirms that discontinuous gas exchange does not contribute to body water conservation in locusts

2016 ◽  
Vol 12 (12) ◽  
pp. 20160807 ◽  
Author(s):  
Stav Talal ◽  
Amir Ayali ◽  
Eran Gefen
Keyword(s):  
Gas Exchange ◽  
Water Loss ◽  
Experimental Evolution ◽  
Water Conservation ◽  
Locusta Migratoria ◽  
Body Water ◽  
Evaporative Water ◽  
Migratory Locust ◽  
Evolutionary Response ◽  
Evolution Study

The adaptive nature of discontinuous gas exchange (DGE) in insects is contentious. The classic ‘hygric hypothesis’, which posits that DGE serves to reduce respiratory water loss (RWL), is still the best supported. We thus focused on the hygric hypothesis in this first-ever experimental evolution study of any of the competing adaptive hypotheses. We compared populations of the migratory locust ( Locusta migratoria ) that underwent 10 consecutive generations of selection for desiccation resistance with control populations. Selected locusts survived 36% longer under desiccation stress but DGE prevalence did not differ between these and control populations (approx. 75%). Evolved changes in DGE properties in the selected locusts included longer cycle and interburst durations. However, in contrast with predictions of the hygric hypothesis, these changes were not associated with reduced RWL rates. Other responses observed in the selected locusts were higher body water content when hydrated and lower total evaporative water loss rates. Hence, our data suggest that DGE cycle properties in selected locusts are a consequence of an evolved increased ability to store water, and thus an improved capacity to buffer accumulated CO 2 , rather than an adaptive response to desiccation. We conclude that DGE is unlikely to be an evolutionary response to dehydration challenge in locusts.

scholarly journals Does control of insensible evaporative water loss by two species of mesic parrot have a thermoregulatory role?

2020 ◽  
Vol 223 (19) ◽  
pp. jeb229930 ◽  
Author(s):  
Christine Elizabeth Cooper ◽  
Philip Carew Withers ◽  
Gerhard Körtner ◽  
Fritz Geiser
Keyword(s):  
Water Loss ◽  
Water Conservation ◽  
Arid Zone ◽  
Evaporative Water Loss ◽  
Primary Role ◽  
Physiological Control ◽  
Evaporative Water ◽  
Ambient Temperatures ◽  
Physiological Variables ◽  
Regulatory Ability

ABSTRACTInsensible evaporative water loss (EWL) at or below thermoneutrality is generally assumed to be a passive physical process. However, some arid zone mammals and a single arid zone bird can control their insensible water loss, so we tested the hypothesis that the same is the case for two parrot species from a mesic habitat. We investigated red-rumped parrots (Psephotus haematonotus) and eastern rosellas (Platycercus eximius), measuring their EWL, and other physiological variables, at a range of relative humidities at ambient temperatures of 20 and 30°C (below and at thermoneutrality). We found that, despite a decrease in EWL with increasing relative humidity, rates of EWL were not fully accounted for by the water vapour deficit between the animal and its environment, indicating that the insensible EWL of both parrots was controlled. It is unlikely that this deviation from physical expectations was regulation with a primary role for water conservation because our mesic-habitat parrots had equivalent regulatory ability as the arid habitat budgerigar (Melopsittacus undulatus). This, together with our observations of body temperature and metabolic rate, instead support the hypothesis that acute physiological control of insensible water loss serves a thermoregulatory purpose for endotherms. Modification of both cutaneous and respiratory avenues of evaporation may be involved, possibly via modification of expired air temperature and humidity, and surface resistance.

Studies of the environmental physiology of tropical merinos

1978 ◽  
Vol 29 (1) ◽  
pp. 161 ◽  
Author(s):  
PS Hopkins ◽  
GI Knights ◽  
AS Le Feuvre
Keyword(s):  
Low Temperature ◽  
Rectal Temperature ◽  
Water Loss ◽  
Heat Dissipation ◽  
Evaporative Water Loss ◽  
Compensatory Mechanisms ◽  
Evaporative Water ◽  
Ambient Temperatures ◽  
Diurnal Patterns ◽  
Made In

Rectal temperature measurements of tropical Merino sheep taken in the sun during summer indicated that there were high and low temperature groups. Animals of low temperature status (e.g. 39.4°C) also exhibited a low respiration rate (e.g. 110/min) in comparison with their less adapted counterparts (40.0° and 190/min). These differences were greatest when ambient temperatures were high. The repeatability of temperature status was 0.46 (P < 0.01). Animals of folds (+) phenotype had significantly higher rectal temperatures than folds (–) animals (P < 0.05). Shearing caused a marked but transient increase in rectal temperature. Compensatory mechanisms apparently involved an increase in cutaneous heat dissipation and/or a decrease in exogenous heat load. Evaporative water loss (80–115 ml/kg/day) greatly exceeded the non-evaporative water loss (40–65 ml/kg/day) of sheep in metabolism cages. Respiratory water loss could account for only 8–10% of the total daily evaporative water loss. Non-respiratory evaporative water loss (as measured by difference) was c. 75–100 ml/kg/day. There were no striking differences between high and low temperature status sheep in this regard. Measurements of respiratory (2 ml/kg/hr) and non-respiratory (5.5 ml/kg/hr) evaporative water loss made in hygrometric tents suggested that the greater non-respiratory water loss was partly due to a higher rate of loss and partly to a longer period of loss per day. This suggestion was supported by the diurnal patterns of rectal temperatures and respiration rates reported here, though no firm conclusions could be made as to the thermotaxic effect of non-respiratory water loss and thermoregulation of tropical Merinos with varying amounts of wool cover.

scholarly journals Environmental determinants of total evaporative water loss in birds at multiple temperatures

The Auk ◽  
2019 ◽  
Vol 137 (1) ◽  
Author(s):  
Soorim Song ◽  
Steven R Beissinger
Keyword(s):  
Water Loss ◽  
Water Conservation ◽  
Heat Dissipation ◽  
Natural Habitat ◽  
Thermal Conditions ◽  
Evaporative Water Loss ◽  
Diel Activity ◽  
Maximum Temperature ◽  
Arid Environments ◽  
Evaporative Water

Abstract Endotherms dissipate heat to the environment to maintain a stable body temperature at high ambient temperatures, which requires them to maintain a balance between heat dissipation and water conservation. Birds are relatively small, contain a large amount of metabolically expensive tissue, and are mostly diurnal, making them susceptible to physiological challenges related to water balance and heat dissipation. We compiled total evaporative water loss (TEWL) measurements for 174 species of birds exposed to different temperatures and used comparative methods to examine their relationships with body size, ambient temperature, precipitation, diet, and diel activity cycle. TEWL in the thermoneutral zone (TNZ) was associated primarily with body mass and activity phase. Larger and more active-phase birds, with their higher metabolic rates, lost more water through evaporation than smaller, resting-phase birds, particularly at higher thermal exposures. However, maximum temperature of the natural habitat became an important determinant of TEWL when birds were exposed to temperatures exceeding the TNZ. Species from hotter climates exhibited higher TEWL. Adaptation to arid climates did not restrict evaporative water loss at thermal conditions within the TNZ, but promoted evaporative water loss at exposures above the TNZ. The TEWL of granivores, which ingest food with low water content, differed little from species with other food habitats under all thermal conditions. The effects of environmental covariates of TEWL were dissimilar across thermal exposures, suggesting no evidence for a tradeoff between water conservation in the TNZ and heat dissipation at exposure to higher temperatures. Thus, birds may be able to acclimate when climate change results in the need to increase heat dissipation due to warming, except perhaps in hot, arid environments where species will need to depend heavily upon evaporative cooling to maintain homeothermy.

Water Metabolism of the Domestic Fowl From Hatching to Maturity

1957 ◽  
Vol 190 (1) ◽  
pp. 139-141 ◽  
Author(s):  
W. Medway ◽  
M. R. Kare
Keyword(s):  
Metabolic Rate ◽  
Basal Metabolic Rate ◽  
Water Loss ◽  
Total Body Water ◽  
Domestic Fowl ◽  
Direct Method ◽  
Body Water ◽  
Water Metabolism ◽  
Evaporative Water ◽  
Total Body

The total evaporative water loss, total body water by the direct method and the basal metabolic rate were determined on domestic fowl at various stages of growth. The trials were conducted on a total of 440 birds. The combined respiratory and cutaneous water loss was high on the 1st day of life, dropped to a minimum between 1 and 2 weeks of age, rose sharply at 2–4 weeks of age, then gradually tapered off to the value observed in the adult. The total body water and the total body water on a fat-free basis was quite high on the 1st day of life, then gradually decreased to that of the adult. The basal metabolic rate was low on the 1st day, rose sharply to a maximum at 2–4 weeks of age and then gradually tapered off to that of the adult.

Evaporative cooling in the rat: Effects of hypothalamic lesions and chorda tympani damage

1970 ◽  
Vol 48 (1) ◽  
pp. 11-17 ◽  
Author(s):  
Edward M. Stricker ◽  
F. Reed Hainsworth
Keyword(s):  
Evaporative Cooling ◽  
Chorda Tympani ◽  
Parasympathetic Innervation ◽  
Evaporative Water ◽  
Ambient Temperatures ◽  
Hypothalamic Lesions ◽  
Effector System ◽  
Peripheral Vasodilatation ◽  
Electrolytic Lesions ◽  
Gland Function

Previous studies have demonstrated the importance of saliva spreading for evaporative cooling by rats in the heat. In particular, submaxillary–sublingual salivary gland function must be unimpaired for the rat to regulate its body temperature at ambient temperatures above 38 °C. The present study investigated some of the neural components of this thermoregulatory effector system. Bilateral destruction of the chorda tympani, the parasympathetic innervation of the submaxillary–sublingual glands, severely impaired the rat's tolerance of high ambient temperatures. Rats with bilateral electrolytic lesions in the anterior or lateral hypothalamus, placed without chorda tympani damage, also showed pronounced deficits in salivary evaporative water loss and impaired thermal tolerances during heat stress. Other heat loss mechanisms, such as peripheral vasodilatation, may also have been disrupted. These results support previous reports of thermoregulatory deficits in rats following hypothalamic lesions.

Energetics of the Little Penguin, Eudyptula Minor: Temperature Regulation, the Calorigenic Effect of Food, and Moulting.

1986 ◽  
Vol 34 (1) ◽  
pp. 35 ◽  
Author(s):  
RV Baudinette ◽  
P Gill ◽  
M O'driscoll
Keyword(s):  
Heat Production ◽  
Water Loss ◽  
Thermal Conductance ◽  
Fold Increase ◽  
The Body ◽  
Evaporative Water Loss ◽  
Evaporative Water ◽  
Ambient Temperatures ◽  
Effect Of Food ◽  
Little Penguin

Rates of oxygen consumption and means of augmenting the resultant heat production were studied in the little penguin, Eudyptula minor. Metabolic rates were lower than those predicted for a 1-kg bird, but shivering and an energy response to feeding were both present. The latter effect was independent of ambient temperatures between 2 deg and 22 deg C. The birds have limited ability to dissipate heat by evaporative water loss. About 40% of the total heat production was the maximum amount lost by this route. Cooling of expired respiratory gas provided an effective saving of heat and water. Moulting resulted in a 1.5-fold increase in metabolic rate but rates of evaporative water loss were reduced. The increase in heat production is correlated with increased thermal conductance across the body surface, as new feathers are synthesized, but body temperature is the same as in non-moulting penguins. The results suggest that increased heat loss when the birds are in water might be replaced by calorigenesis associated with the response to feeding, and by shivering, as well as by activity.

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