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Division of Pediatric Cardiology and Thoracic Surgery, Beatrix Children's Hospital, University of Groningen, 9700 RB Groningen; and Groningen Utrecht Institute for Drug Exploration, 9713 BZ Groningen, The Netherlands
Free fatty acids are the major fuels for the
myocardium, but during a higher load carbohydrates are preferred.
Previously, we demonstrated that myocardial net lactate uptake was
higher in lambs with aortopulmonary shunts than in control lambs. To determine whether this was caused by an increased lactate uptake and
oxidation or by a decreased lactate release, we studied myocardial lactate and glucose metabolism with
13C-labeled substrates in 36 lambs
in a fasting, conscious state. The lambs were assigned to two groups: a
resting group consisting of 8 shunt and 9 control lambs, and an
exercise group (50% of peak O2
consumption) consisting of 9 shunt and 10 control lambs. Myocardial
lactate oxidation was higher in shunt than in control lambs (mean ± SE, rest: 10.33 ± 2.61 vs. 0.17 ± 0.82, exercise: 38.05 ± 8.87 vs. 16.89 ± 4.78 µmol · min
1 · 100 g
1;
P < 0.05). There was no difference
in myocardial lactate release between shunt and control lambs.
Oxidation of exogenous glucose, which was approximately zero at rest,
increased during exercise in shunt and control lambs. The contribution
of glucose and lactate to myocardial oxidative metabolism increased
during exercise compared with at rest in both shunt and control lambs.
We conclude that myocardial lactate oxidation is higher in shunt than
in control lambs, both at rest and during exercise, and that the
contribution of carbohydrates in myocardial oxidative metabolism in
shunt lambs is higher than in control lambs. Thus it appears that this
higher contribution of carbohydrates occurs not only in the case of
pressure-overloaded hearts but also in myocardial hypertrophy due to
volume overloading.
carbon-13-labeled substrates; congenital heart disease; left-to-right shunt; glucose; metabolism
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