Effects of Warm Temperatures on Metabolic Rate and Evaporative Water Loss in Tuatara, a Cool-Climate Rhynchocephalian Survivor

Total evaporative water loss of endotherms is assumed to be determined essentially by biophysics, at least at temperatures below thermoneutrality, with evaporative water loss determined by the water vapor deficit between the animal and the ambient air. We present here evidence, based on the first measurements of evaporative water loss for a small mammal in heliox, that mammals may have a previously unappreciated ability to maintain acute constancy of total evaporative water loss under perturbing environmental conditions. Thermoregulatory responses of ash-grey mice ( Pseudomys albocinereus) to heliox were as expected, with changes in metabolic rate, conductance, and respiratory ventilation consistent with maintaining constancy of body temperature under conditions of enhanced heat loss. However, evaporative water loss did not increase in heliox. This is despite our confirmation of the physical effect that heliox augments evaporation from nonliving surfaces, which should increase cutaneous water loss, and increases minute volume of live ash-grey mice in heliox to accommodate their elevated metabolic rate, which should increase respiratory water loss. Therefore, mice had not only a thermoregulatory but also a hygroregulatory response to heliox. We interpret these results as evidence that ash-grey mice can acutely control their evaporative water loss under perturbing environmental conditions and suggest that hygroregulation at and below thermoneutrality is an important aspect of the physiology of at least some small mammals.

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Novel approaches to the calculation and comparison of thermoregulatory parameters: Non-linear regression of metabolic rate and evaporative water loss in Australian rodents

Journal of Thermal Biology ◽

10.1016/j.jtherbio.2016.01.012 ◽

2016 ◽

Vol 57 ◽

pp. 54-65 ◽

Cited By ~ 5

Author(s):

Sean Tomlinson

Keyword(s):

Linear Regression ◽

Metabolic Rate ◽

Water Loss ◽

Evaporative Water Loss ◽

Evaporative Water ◽

Non Linear ◽

Novel Approaches

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Inhibitors of nitric oxide synthesis block cold-induced thermogenesis in rats

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y03-069 ◽

2003 ◽

Vol 81 (8) ◽

pp. 834-838 ◽

Cited By ~ 10

Author(s):

Peter R Kamerman ◽

Helen P Laburn ◽

Duncan Mitchell

Keyword(s):

Nitric Oxide ◽

Methyl Ester ◽

Body Temperature ◽

Nitric Oxide Synthase ◽

Metabolic Rate ◽

Water Loss ◽

T Test ◽

Evaporative Water Loss ◽

Evaporative Water ◽

Oxide Synthase

N-nitro-L-arginine methyl ester (L-NAME), an unspecific nitric oxide synthase inhibitor, was administered to individually caged SpragueDawley rats exposed to cold (18°C) and thermoneutral (30°C) environmental temperatures during the active phase of the animals' circadian cycle. Unrestrained rats were administered intraperitoneal injections of 100 mg·kg1 L-NAME or 1 mL·kg1 saline. Telemetry was used to measure abdominal temperature. On a separate occasion, metabolic rate and evaporative water loss were measured using indirect calorimetery, before and after the injection of 100 mg·kg1 L-NAME, in rats exposed to the two environments. Injection of L-NAME had no significant effect on body temperature, metabolic rate, or evaporative water loss in rats exposed to the 30°C environment. In the 18°C environment, L-NAME injection caused a prolonged fall in body temperature (F(1,12) = 17.43, P = 0.001) and a significant decrease in metabolic rate (Student's t test, P = 0.001) and evaporative water loss (one-sample t test, P = 0.04). Therefore, the effects that systemic injection of L-NAME has on body temperature are dependent on environmental temperature, with nitric oxide synthase inhibition seemingly preventing the metabolic component of cold defence.Key words: N-nitro-L-arginine methyl ester, thermoregulation, telemetry, oxygen consumption.

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