AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 3 641-R650, Copyright © 1995 by American Physiological Society
Relationship between body mass, tissue metabolic rate, and sodium pump activity in mammalian liver and kidney
P. Couture and A. J. Hulbert
Department of Biological Sciences, University of Wollongong, New South Wales, Australia.
The allometric relationship between body mass and tissue metabolism was
examined in liver and kidney cortex slices from mouse, rat, rabbit, sheep,
and cattle, representing an approximately 12,000-fold difference in body
mass and an 11-fold difference in mass-specific basal metabolic rate.
Larger mammals have lower tissue metabolic rates (TMR; mumol O2.g wet
wt-1.min-1) at 37 degrees C, yielding the equations TMR = 3.6 M-0.21 for
liver slices and TMR = 3.2 M-0.11 for kidney cortex slices, where M is body
mass in grams. This appears to be an intrinsic property of the tissue and
is not due to differences in extracellular space or tissue protein content,
because these are relatively constant in all mammalian species examined.
The allometric relationships remain when tissue metabolism is expressed
relative to "active cell mass" in tissue slices. Potassium uptake rate
(KUR; mumol K+.g wet wt-1.min-1) was also measured (as 86Rb+ uptake) and
was also lower in larger mammals, yielding the equations KUR = 1.2 M-0.14
in liver slices and KUR = 3.4 M-0.13 for kidney cortex slices. The
energetic costs of sodium pump activity were estimated to be < 10% of
TMR for liver and kidney cortex from all five mammalian species.
