| Effect of
Starvation on Branched-Chain a-Keto Acid
Dehydrogenase Activity in Rat Heart and Skeletal
Muscle M. HOLEČEK
Department of Physiology, Faculty of
Medicine, Charles University, Hradec Králové,
Czech Republic
Received
December 27, 1999
Accepted April 12, 2000
Summary
The
aim of the present study was to investigate
changes in the activity of branched-chain a-keto
acid dehydrogenase (BCKAD) in skeletal muscle and
the heart during brief and prolonged starvation.
Fed control rats and rats starved for 2, 4 and 6
days were anesthetized with pentobarbital sodium
before heart and hindlimb muscles were frozen in
situ by liquid nitrogen. Basal (an estimate of in
vivo activity) and total (an estimate of enzyme
amount) BCKAD activities were determined by
measuring the release of 14CO2 from
a-keto[1-14C]isocaproate. The activity state of
BCKAD complex was calculated as basal activity in
percentages of total activity. Both basal and
total activities and the activity state of the
BCKAD were lower in skeletal muscles than in the
heart. In both tissues, starvation for 2 or 4
days caused a decrease in the basal activity and
activity state of BCKAD. On the contrary, in the
heart and muscles of animals starved for 6 days a
marked increase in basal activity and activity
state of BCKAD was observed. The total BCKAD
activity was increasing gradually during
starvation both in muscles and the heart. The
increase was significant in muscles on the 4th
and 6th day of starvation. The demonstrated
changes in BCKAD activity indicate significant
alterations in branched-chain amino acid (BCAA)
and protein metabolism during starvation. The
decreased BCKAD activity in skeletal muscle and
heart observed on the 2nd and 4th day of
starvation prevents the loss of essential BCAA
and is an important factor involved in protein
sparing. The increased activity of BCKAD on the
6th day of starvation indicates activated
oxidation of BCAA and accelerated protein
breakdown.
Key
words
Branched-chain
amino acids · Leucine · Fasting · Protein
metabolism
Reprint
requests
Dr. Milan Holeček, Department of Physiology,
Charles University, Faculty of Medicine, Šimkova
870, 500 01 Hradec Králové, Czech Republic, fax
+420-49-5210190, e-mail: holecek@lfhk.cuni.cz
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