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Matching oxygen supply and oxygen demand : do heterothermic rodents tolerate cold and hypoxia through the retention of neonatal traits?

University of British Columbia

There are striking similarities between newborn mammals and adult mammals capable of hibernation (heterotherms) that are not present in adult mammals that do not hibernate (homeotherms). Unlike most mammals, adult heterotherms and newborns are exceptionally tolerant of cold and hypoxia. However, the basis of this enhanced tolerance remains largely unknown. In this thesis I determined how newborn and adult rodents that vary in heterothermic expression match O₂ supply and O₂ demand when exposed to cold and hypoxia, either alone, or in combination. I hypothesized that this enhanced tolerance reflects the retention of newborn responses in adult heterotherms that are not present in adult homeotherms. This thesis has shown that the responses rodents use to match O₂ supply and O₂ demand vary with age, O₂ level, ambient temperature, and degree of heterothermic expression. When exposed to cold alone all newborns significantly decreased their body temperature, O₂ consumption rate, and ventilation. However, as adults all rodents maintained a high body temperature by increasing or maintaining their O₂ consumption rate and ventilation. When exposed to hypoxia alone, I found that all rodents used similar responses to match O₂ supply and O₂ demand. Newborn and adult, homeotherms and heterotherms alike all reduced their metabolic demand for O₂ and increased O₂ supply by increasing their ventilation. When exposed to both hypoxia and cold, however, adult heterotherms exhibited a greater reduction in O₂ consumption rates, and a reduced ventilatory response compared to adult homeotherms, responses more similar to those of newborns when they were exposed to hypoxia and cold. My thesis supports the hypothesis that heterotherms match O₂ supply and O₂ demand through the retention newborn responses, but only when exposed to hypoxia in the cold, as: (1) homeotherms and heterotherms both differed in their responses to cold as newborns and adults; and (2) all rodents used similar responses when exposed to hypoxia alone. These data provide insight into the basis of enhanced cold and hypoxia tolerance of adult heterotherms and newborns.

Text

2018-05-14

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/65858

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/