Journal of Applied Physiology, Vol 69, Issue 4 1244-1251, Copyright © 1990 by American Physiological Society
Splanchnic and muscle fructose metabolism during and after exercise
G. Ahlborg and O. Bjorkman
Department of Clinical Physiology, Huddinge Hospital, Sweden.
Regional substrate exchange was studied in 12 healthy males during 90 min
of bicycle exercise at 30% of maximal O2 consumption with a 20-min
recovery. Six subjects received an intravenous fructose infusion (8.5
mmol/min) from 40 min of exercise to the end of recovery. Splanchnic
glucose output, muscle glucose uptake, arterial glucose, and insulin were
uninfluenced by the infusion. The respiratory exchange ratio rose to 0.93
+/- 0.04, and arterial free fatty acids fell by 50% (P less than 0.05).
Fructose was taken up by splanchnic tissues (45% of administered load), leg
muscle (28%), and resting muscle (28%). During infusion, arterial lactate
and pyruvate rose two- to threefold, and these substrates were released
from splanchnic tissues and taken up by exercising and resting muscle.
Splanchnic release of lactate, pyruvate, and glucose accounted for 78% of
fructose uptake at 90 min of exercise. Uptake of fructose, lactate, and
pyruvate accounted for 55% and together with glucose for 103% of the total
oxidative metabolism by exercising muscle. The regional fructose uptakes
and lactate exchanges persisted throughout recovery. The present results
indicate that fructose infusion during leg exercise 1) results in increased
carbohydrate oxidation from fructose, lactate, and pyruvate in exercising
muscle, 2) exerts a glycogenic effect in resting muscle and liver during
exercise and in liver and muscle recovering from exercise, and 3) does not
interfere with glucose metabolism, and that fructose transport into muscle
differs from that of glucose.
