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Acid-base balance in the developing marsupial: from ectotherm to endotherm


Andrewartha, SJ and Cummings, KJ and Frappell, PB, Acid-base balance in the developing marsupial: from ectotherm to endotherm, Journal of Applied Physiology, 116, (9) pp. 1210-1219. ISSN 8750-7587 (2014) [Refereed Article]

Copyright Statement

Copyright 2014 the American Physiological Society

DOI: doi:10.1152/japplphysiol.00996.2013


Marsupial joeys are born ectothermic and develop endothermy within their mother's thermally stable pouch. We hypothesized that Tammar wallaby joeys would switch from α-stat to pH-stat regulation during the transition from ectothermy to endothermy. To address this, we compared ventilation (V̇e), metabolic rate (V̇o2), and variables relevant to blood gas and acid-base regulation and oxygen transport including the ventilatory requirements (V̇e/V̇o2 and V̇e/V̇co2), partial pressures of oxygen (PaO2), carbon dioxide (PaCO2), pHa, and oxygen content (CaO2) 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 (∼1516C in both species). Ectothermic joeys displayed limited thermogenic ability during cooling: after an initial plateau, V̇o2 decreased with the progressive drop in Tb. The Tb of endothermic joeys and rats fell despite V̇o2 nearly doubling with the initiation of cold stress. In all three groups the changes in V̇o2 were met by changes in V̇e, resulting in constant V̇e/V̇o2 and V̇e/V̇co2, 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.

Item Details

Item Type:Refereed Article
Keywords:Tammar wallaby (Macropus eugenii), Sprague-Dawley rat, thermoregulation, ventilatory requirement, acid-base balance
Research Division:Biological Sciences
Research Group:Zoology
Research Field:Animal developmental and reproductive biology
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the biological sciences
UTAS Author:Andrewartha, SJ (Dr Sarah Andrewartha)
UTAS Author:Frappell, PB (Professor Peter Frappell)
ID Code:98919
Year Published:2014
Web of Science® Times Cited:5
Deposited By:Zoology
Deposited On:2015-03-06
Last Modified:2017-10-31

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