Jr. Speakman et Ms. Johnson, Relationships between resting metabolic rate and morphology in lactating mice: What tissues are the major contributors to resting metabolism?, LIFE IN THE COLD, 2000, pp. 479-486
We sought the relationship between resting metabolic rate (RMR) and gross t
issue morphology in 59 lactating female MFI mice. RMR was measured at peak
lactation (Day 18 post partum) and the animals were then immediately killed
and dissected into 18 separate components which were dried for 14 days at
60 degreesC. Individual variation in the RMR (CV) was 27%. The masses of th
e tissue components were similarly variable (CV ranging from 4.3% for the b
rain to around 150% for fat tissue). RMR was significantly related to overa
ll body mass (r(2) = 0.458) with a scaling exponent of 1.55. Similar signif
icant relationships were evident between masses of most (16/18) of the tiss
ues and overall body mass. Accordingly there were significant relationships
between RMR and all the tissue masses with the exception of those tissues
poorly related to overall body mass (specifically the lungs, small intestin
e, brain and kidneys). When the shared variation due to total body mass was
eliminated there were no significant links between residual RMR and residu
al In;lss of any tissue. Re-describing the morphology using principal compo
nents analysis revealed a link between a general size component (PC1) and R
MR (r(2) = 0.374) but this relationship disappeared when residual RMR was e
mployed as the dependent variable. Despite other studies that indicate wide
variations in the rates at which different tissues metabolise energy ill v
itro there was no indication in the present study that any particular compo
nent of the morphology was linked to high RMR in vivo.