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Departments of 1 Physiology and Biophysics, 2 Nutrition, and 4 Pharmacology and Medicine, Case Western Reserve University, Cleveland, Ohio 44106-7139; and 3 Department of Nutrition, University of Montreal, Montreal, Quebec, Canada H3C 3J7
Normal cardiac metabolism requires
continuous replenishment (anaplerosis) of catalytic intermediates of
the citric acid cycle. Little is known about the quantitative aspects
of propionate as a substrate of in vivo anaplerosis; therefore, we
measured the rate of propionate entry into the citric acid cycle in
hearts of anesthetized pigs.
[U-13C3]propionate (0.25 mM) was infused in a
coronary artery branch for 1 h via an extracorporeal perfusion
circuit, and cardiac biopsies were analyzed for the mass isotopomer
distribution of citric acid cycle intermediates. Infusion of propionate
did not affect myocardial oxygen consumption, heart rate, or
contractile function. In the infused territory, propionate infusion did
not affect uptake of glucose and lactate but decreased free fatty acid
uptake by one-half (P < 0.05). Propionate extraction
and uptake were 57.4 ± 3.3% and 0.078 ± 0.009 µmol · min
1 · g
1.
Anaplerosis from propionate, calculated from the mass isotopomer distribution of succinate, accounted for 8.9 ± 1.3% of the
citric acid cycle flux. Propioylcarnitine release accounted for only 0.033 ± 0.002% of propionate uptake. Methylcitrate did not
accumulate. Thus administration of a low concentration of propionate
appears to be a convenient and safe way to boost anaplerosis in the heart.
tricarboxylic acid cycle; cataplerosis; mass isotopomer analysis; mass spectrometry
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