科研之友
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摘要
Marsupial joeys are born ectothermic and develop endothermy within their mother%26apos;s thermally stable pouch. We hypothesized that Tammar wallaby joeys would switch from alpha-stat to pH-stat regulation during the transition from ectothermy to endothermy. To address this, we compared ventilation (V-E), metabolic rate (V-O2), and variables relevant to blood gas and acid-base regulation and oxygen transport including the ventilatory requirements (V-E/V-O2 and V-E/V-CO2), partial pressures of oxygen (Pa-O2), carbon dioxide (Pa-CO2), pHa, and oxygen content (Ca-O2) during progressive hypothermia in ecto- and endothermic Tammar wallabies. We also measured the same variables in the well-studied endotherm, the Sprague-Dawley rat. Hypothermia was induced in unrestrained, unanesthetized joeys and rats by progressively dropping the ambient temperature (Ta). Rats were additionally exposed to helox (80% helium, 20% oxygen) to facilitate heat loss. Respiratory, metabolic, and blood-gas variables were measured over a large body temperature (Tb) range (similar to 15-16 degrees C in both species). Ectothermic joeys displayed limited thermogenic ability during cooling: after an initial plateau, V-O2 decreased with the progressive drop in Tb. The Tb of endothermic joeys and rats fell despite V-O2 nearly doubling with the initiation of cold stress. In all three groups the changes in V-O2 were met by changes in V-E, resulting in constant V-E/V-O2 and V-E/VCO2, blood gases, and pHa. Thus, although thermogenic capability was nearly absent in ectothermic joeys, blood acid-base regulation was similar to endothermic joeys and rats. This suggests that unlike some reptiles, unanesthetized mammals protect arterial blood pH with changing Tb, irrespective of their thermogenic ability and/or stage of development.
- 出版日期2014-5
- 单位CSIRO
