Journal of Applied Physiology, Vol 66, Issue 5 2117-2123, Copyright © 1989 by American Physiological Society
Skeletal muscle O2 consumption and energy metabolism during hypoxemia
G. Gutierrez, R. J. Pohil and P. Narayana
Pulmonary Division, University of Texas Health Science Center, Houston 77030.
We determined the relationship of O2 transport (TO2) to O2 consumption
(VO2) and to changes in cellular bioenergetics in an isolated
blood-perfused rabbit hindlimb preparation (n = 8) during hypoxemia. The
preparations were subjected to reductions in TO2 by progressively
decreasing partial pressure of arterial O2 (PaO2). At each level of PaO2 we
obtained simultaneous measures of arterial and venous blood gases, venous
lactate concentration, and changes in the relative concentrations of
inorganic phosphate, phosphocreatine, and ATP measured with 31P magnetic
resonance spectroscopy. The ratio of the change in vascular resistance (R)
to the corresponding decrease in TO2 was taken as an index of vascular
autoregulation with hypoxemia. Linear and logarithmic functions were fitted
by least squares to the TO2-VO2 data from each experiment. TO2-VO2
relationships were characterized as O2 conforming (linear function, n = 4)
or O2 regulating (logarithmic function, n = 4), depending on the goodness
of fit. Those preparations showing an O2-conforming pattern had higher
control VO2 (2.42 +/- 0.14 vs. 1.66 +/- 0.19 ml.min-1.kg-1; P less than
0.05) and a lesser degree of vascular autoregulation (0.07 +/- 0.03 vs.
0.21 +/- 0.02; P less than 0.01) than the O2-regulating group. Decreases in
VO2 were always accompanied by increases in inorganic phosphate and lactate
and decreases in phosphocreatine, indicating O2 supply limitation and
anaerobic ATP production. There was no evidence of cellular adaptation to
hypoxia by decreasing energy needs or of VO2 limitation by the depletion of
adenine nucleotides.
