AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 5 1217-R1223, Copyright © 1995 by American Physiological Society
Vasoconstrictors alter oxygen, lactate, and glycerol metabolism in the perfused hindlimb of a rat kangaroo
J. M. Ye, S. J. Edwards, R. W. Rose, S. Rattigan, M. G. Clark and E. Q. Colquhoun
Department of Biochemistry, University of Tasmania, Hobart, Australia.
The Tasmanian bettong (Bettongia gaimardi) is a small marsupial rat
kangaroo without detectable brown adipose tissue (BAT). The hindlimb was
perfused with constant flow at 25 degrees C after cannulation under
anesthesia of the femoral artery and vein to one hindlimb. Norepinephrine
(NE, 25 nM-2.5 microM) and vasopressin (VP, 10 nM-0.1 microM) each
increased perfusion pressure, oxygen consumption (VO2), and lactate and
glycerol efflux of the perfused hindlimb. NE-mediated increases in VO2 and
the efflux of lactate and glycerol were unaffected by propranolol (10
microM) but were completely blocked by the further addition of phentolamine
(10 microM). In contrast, serotonin (5-HT; 0.1-2.5 microM) inhibited VO2
and inhibited lactate efflux. The changes induced by NE, VP, and 5-HT were
all rapidly reversed by nitroprusside. These results suggest that resting
thermogenesis in bettong hindlimb can be differentially controlled by the
vasculature, which may also contribute to the induced VO2. This vascular
control of skeletal muscle VO2 appears widespread in homeotherm evolution.
