Marsupials lack brown adipose tissue, and therefore rely exclusively on other tissues for thermogenesis. To determine the magnitude of phenotypic plasticity of the liver in response to changing metabolic demand, gray short-tailed opossums (M. domestica) were exposed to thermoneutral (28°C) or cold (9-12°C) conditions continuously for 6 weeks. Half of each group was also endurance trained with a treadmill program during their respective temperature exposure. Mass specific summit metabolism (V̇O 2summit) increased 11% following cold acclimation, though there was no significant main effect by training on V̇O2summit. To estimate the contribution of the liver to whole animal oxidative activity, we determined liver mass, mitochondrial volume density, and total mitochondrial volume. Relative liver mass was 48% greater in cold-acclimated animals, whereas training had no effect on liver mass. The stereological analysis of hepatocyte ultrastructure suggests the percentage of intracellular volumes remained unchanged in response to either aerobic challenge. Thus, following cold-acclimation, there is a 20% increase in the total mitochondrial volume of the liver. This increase could account for nearly half (44%) of the observed increase in whole animal V̇O2summit following cold exposure.
|Number of pages
|Comparative Biochemistry and Physiology - A Molecular and Integrative Physiology
|Published - Nov 2003
All Science Journal Classification (ASJC) codes
- Aquatic Science
- Animal Science and Zoology
- Molecular Biology