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Acid-base balance in the developing marsupial: from ectotherm to endotherm
Sarah J Andrewartha1, Kevin J Cummings, Peter B Frappell
1University of Tasmania, Hobart, Tasmania, Australia;
Journal of Applied Physiology (Bethesda, Md. : 1985)
|March 15, 2014
Summary
Marsupial joeys transition from ectothermy to endothermy, maintaining blood pH regulation. Mammals protect arterial blood pH regardless of thermogenic ability or developmental stage.
Area of Science:
- Comparative physiology
- Mammalian development
- Thermoregulation
Background:
- Marsupial joeys are born ectothermic and develop endothermy in the maternal pouch.
- The transition from ectothermy to endothermy involves changes in physiological regulation.
- Understanding acid-base balance during this transition is crucial for mammalian survival.
Purpose of the Study:
- To test the hypothesis that Tammar wallaby joeys switch from alpha-stat to pH-stat regulation during the ectotherm-to-endotherm transition.
- To compare blood gas and acid-base regulation during hypothermia in ectothermic and endothermic wallaby joeys and Sprague-Dawley rats.
- To investigate the relationship between thermogenic ability and blood pH protection in developing mammals.
Main Methods:
- Progressive hypothermia was induced in unrestrained, unanesthetized wallaby joeys and rats by lowering ambient temperature.
- Respiratory (ventilation, metabolic rate) and blood gas variables (PaO2, PaCO2, pHa) were measured across a wide body temperature range.
- Rats were exposed to heliox to facilitate heat loss and further assess thermoregulatory responses.
Main Results:
- Ectothermic joeys showed limited thermogenesis, with metabolic rate decreasing as body temperature dropped.
- Endothermic joeys and rats maintained elevated metabolic rates but still experienced falling body temperatures under cold stress.
- Despite differences in thermogenic capacity, ventilation adjusted to maintain constant ventilatory requirements (Ve/Vo2, Ve/Vco2), blood gases, and arterial pHa in all groups.
Conclusions:
- Mammalian joeys and rats maintain arterial blood pH homeostasis during hypothermia, irrespective of their thermogenic ability or developmental stage.
- Unlike some reptiles, mammals appear to protect arterial blood pH through physiological adjustments rather than solely relying on thermoregulation.
- The findings suggest a conserved mechanism for blood acid-base balance in mammals during thermal stress.
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