Effect Of Chronic Exercise On The Activity Of Carnitine Palmitoy-transferase And 3-hydroxyacyl-coa Dehydrogenase In Rat Tissues

Introduction
Chronic endurance exercise increases the rates of fatty acid transport into the mitochondria and β-oxidation. These
increments have been associated with the upregulation of carnitine palmitoyltransferase (CPT) and 3-hydroxyacyl-CoA
dehydrogenase (HAD), a key enzyme of β-oxidation. The purpose of the present study was to investigate the effect of
long-term wheel running, a stress-free exercise model on which no relevant data are available, on the activity of CPT
and HAD in rat gastrocnemius muscle, liver, heart, and adipose tissue.

Methods
Thirty-four male Wistar rats at the age of 7 weeks were divided randomly into a trained (n = 20) and an untrained group
(n = 14). The rats of the trained group exercised ad libitum for 8 weeks in cages equipped with a wheel. Upon
completion of the training period, the eleven most active trained animals (having run, on average, over 2 km/d) and the
untrained animals were decapitated and their gastrocnemius medialis, liver, heart, epididymal adipose tissue and
subcutaneous adipose tissue (from the buttock area) were removed. The maximal activities of CPT and HAD were
measured spectrophotometrically and were expressed in U/g wet tissue, one U corresponding to one μmol of the
appropriate substrate converted per min. Differences between trained and untrained animals were examined by twotailed
independent Student’s t tests. To determine the meaningfulness of the effect of exercise, effect sizes were
calculated as the difference between means divided by the SD of the untrained group.

Results
CPT and HAD activities were significantly higher in the gastrocnemius muscle of the trained rats (table). The
percentage increases were 55 and 22 %, respectively, while the effect sizes were 1.14 and 1.13, respectively. There were
no differences in the activity of the two enzymes in liver or heart, whereas neither CPT nor HAD were detectable inadipose tissue.

Discussion/Conclusions:

Judging from the magnitude of the percentage increases and the effect sizes in gastrocnemius,
there was a large possitive effect of chronic voluntary exercise on enzymes related to fatty acid degradation in rat
skeletal muscle. Noticeable is the higher activity of HAD compared to CPT in all tissues examined, indicating that fatty
acid transport into the mitochondria is the rate-limiting step in fatty acid mitochondrial metabolism. In conclusion, longterm
wheel running increased CPT and HAD activity in rat skeletal muscle and had no effect in liver or heart.

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