Department of Biology and Centre for Forest Interdisciplinary Research, University of Winnipeg, Winnipeg, Manitoba, Canada.
Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.
Exp Physiol. 2021 Apr;106(4):1005-1023. doi: 10.1113/EP089085. Epub 2021 Mar 8.
What is the central question of this study? Adult homeotherms and heterotherms differ in cold and hypoxia tolerance and in how they match O supply and demand in response to these stressors. It has never been ascertained whether these differences reflect different developmental trajectories or whether they are already present at birth. What is the main finding and its importance? When exposed to cold and hypoxia, newborn rodents differed in how they matched O supply and demand, with responses reflecting the degree of heterothermic expression and tolerance. Our findings indicate that elements of the adult phenotype are already present at birth.
There are physiological differences in how adult rodents regulate O supply and O demand when exposed to hypoxia in the cold. We examined whether these differences reflect divergent developmental trajectories of homeotherms and heterotherms or whether the differences are already present at birth. We exposed newborn rodents (0-4 days old) that ranged in heterothermic expression [a homeotherm, the rat (Rattus norvegicus); two facultative heterotherms, the mouse (Mus musculus) and the hamster (Mesocricetus auratus); and an obligate heterotherm, the ground squirrel (Ictidomys tridecemlineatus)] to either normoxia (21% O ) or hypoxia (7% O ) and measured their metabolic, thermoregulatory and ventilatory responses while progressively reducing the ambient temperature from 33 to 15°C. All newborns reduced their body temperature, O consumption rate and ventilation during progressive cooling, both in normoxia and in hypoxia. When progressively cooled in hypoxia, however, the homeothermic rats exhibited the greatest thermogenic response, depressed their O consumption rate the least and increased ventilation the most. In contrast, the obligate heterotherm, the ground squirrel, did not mount a thermogenic response, exhibited the greatest reduction in O consumption rate and increased O uptake not by increasing ventilation like the rat, but by extracting ≤80% of the O from each breath. Facultative heterotherms (mice and hamsters) exhibited responses in between these two extreme phenotypes. We conclude that even as newborns, homeotherms and heterotherms diverge in how they match O supply and O demand when progressively cooled in hypoxia, with responses reflecting the degree of heterothermic expression, in addition to reported hypoxia and cold tolerance.
本研究的核心问题是什么？成年恒温动物和异温动物在对寒冷和缺氧的耐受性以及对这些应激源的氧供应和需求匹配方面存在差异。尚未确定这些差异是否反映了不同的发育轨迹，或者它们是否在出生时就已经存在。主要发现及其重要性是什么？当暴露于寒冷和缺氧环境中时，新生啮齿动物在氧供应和需求的匹配方式上存在差异，其反应反映了异温表达和耐受性的程度。我们的研究结果表明，成年表型的某些元素在出生时就已经存在。
当处于寒冷环境中的低氧环境中时，成年啮齿动物在调节氧供应和氧需求方面存在生理差异。我们研究了这些差异是否反映了恒温动物和异温动物的不同发育轨迹，或者这些差异是否在出生时就已经存在。我们将新生啮齿动物（0-4 日龄）暴露于常氧（21%O ）或低氧（7%O ）环境中，然后逐渐降低环境温度从 33°C 降至 15°C，同时测量其代谢、体温调节和通气反应。所有新生动物在逐渐降温过程中均降低了体温、耗氧量和通气量，无论是在常氧还是低氧环境中。然而，当在低氧环境中逐渐降温时，恒温动物大鼠表现出最大的产热反应，降低耗氧量最少，增加通气量最多。相比之下，作为强制异温动物的地松鼠并没有表现出产热反应，其耗氧量降低最大，并且通过增加呼吸量来增加氧气摄取量，而不是像大鼠那样增加通气量。而强制异温动物地松鼠并没有表现出产热反应，而是通过增加呼吸量来增加氧气摄取量，而不是像大鼠那样增加通气量。此外， facultative heterotherms（鼠和仓鼠）的反应则介于这两种极端表型之间。我们得出结论，即使是新生动物，在低氧环境中逐渐降温时，恒温动物和异温动物在氧供应和氧需求的匹配方面也存在差异，反应反映了异温表达的程度，此外还反映了对缺氧和寒冷的耐受性。
