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Department of Kinesiology and Diabetes Research Center, University of Southern California, Los Angeles, California 90089
The purpose of the present study was to
examine the utilization of fatty acids (FA) and muscle substrates by
skeletal muscle in young, middle-aged, and old adult rats under
conditions of euglycemia with low insulin levels. Male Fischer 344 × Brown Norway rats aged 5, 15, or 24 mo underwent hindlimb perfusion
with a medium of 8 mM glucose, 1 mM palmitate, 25 µU/ml insulin,
[1-14C]palmitate, and [3-3H]glucose.
Glucose and palmitate uptake were similar among age groups. The percent
and total palmitate oxidized
(nmol · min
1 · g
1) were
30-36 and 41-49% lower (P < 0.05) in 15-mo-
and 24-mo-old than in 5-mo-old animals. Compared with 5-mo- and
15-mo-old animals, pre- and postperfusion muscle triglyceride (TG)
levels were significantly (P < 0.05) elevated
91-305% in red and 118-219% in white muscles of 24-mo-old
animals. Fatty acid-binding protein content was 40-64% higher
(P < 0.05) in 24-mo- than in 5-mo- or 15-mo-old
animals. In red muscle, hormone-sensitive lipase (HSL) content was 28% lower (P < 0.05) in 24-mo- than in 5-mo-old animals.
These results indicate that, under euglycemic conditions in the
presence of low insulin levels, the reduction in FA disposal to
oxidation and the decrease in HSL content may contribute to the
accumulation of TG in muscle of old animals.
fatty acid metabolism; fatty acid-binding protein; Fischer 344 × Brown Norway rats; glycogen; intramuscular triglycerides
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