Regulation of fatty acid oxidation in untrained versus trained men
during exercise.
Sidossis, Labros S., Robert R. Wolfe, and Andrew R. Coggan.
Metabolism Unit, Shriners Burns Institute, Galveston, TX and the
Departments of Surgery and Anesthesiology, University of Texas
Medical Branch, Galveston, TX 77550.
APStracts 4:0272E, 1997.
We have recently shown that increased carbohydrate flux decreases fat
oxidation during exercise by inhibition of fatty acid entry into the
mitochondria. Since endurance training reduces the rate of
carbohydrate flux during exercise, we hypothesized that training
increases fat oxidation by relieving this inhibition. To test this
hypothesis, five sedentary and five endurance trained men exercised
on a cycle ergometer at a VO2 of 2.0 L/min, representing 80% and 40%
VO2 peak, respectively. [1-13C]Oleate and [1-14C]octanoate, long- and
medium-chain fatty acids respectively, were infused for the duration
of the studies. Carbohydrate oxidation was significantly higher in
the sedentary group (196+/-9 vs 102+/-17 [grave]imol.kg-1.min-1, P<
0.05). Oleate oxidation was higher in the trained (3.8+/-0.6 vs
1.9+/-0.3 [grave]imol.kg-1.min-1, P< 0.05) whereas octanoate
oxidation was not different between the two groups. The percentage of
oleate that was taken up by tissues and oxidized was higher in the
trained (76+/-7% vs 58+/-3%, P< 0.05). However, the percentage
octanoate taken up and oxidized was not different (82+/-3% vs 85+/
-4%, NS). Since octanoate, unlike oleate, can freely diffuse across
the mitochondrial membrane, the present results suggest that the
difference in fatty acid oxidation between trained and untrained
individuals may be due to enhanced fatty acid entry into the
mitochondria.
Received 22 July 1997; accepted in final form 25 November 1997.
APS Manuscript Number E342-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997