Carbohydrate homeostasis and post-exercise ketosis in trained and untrained rats

1. Experiments were carried out to establish what relationship there is between the concentration of ketone bodies in the blood and the concentrations of glycogen in muscle and liver of thirty-six trained and thirty-six untrained rats exercised at the same absolute load. There were, in addition, non-exercised control animals (of which thirty-six were trained and thirty-six untrained) which were studied on the same day. 2. Training occurred on a level treadmill at 0.2 m/s for 1 h/day, 5 days a week, for 6 weeks. The untrained animals ran on the treadmill every 3rd day for 5 min to maintain familiarity with treadmill running without training them. 3. At the end of the 6th week, the experimental animals ran for 1 h at 0.2 m/s on a level treadmill. Blood 3-hydroxybutyrate and tissue glycogen concentrations were measured at the beginning and immediately after exercise, and then every 30 min for 2 h. 4. Physically trained rats had higher pre- and immediate post-exercise liver glycogen concentrations than untrained rats: 413 +/- 15 and 300 +/- 8 mumol/g before exercise in trained and untrained rats respectively, and 225 +/- 8 and 166 +/- 3 mumol/g immediately after (P less than 0.05). 5. Muscle glycogen, which was also higher in trained than in untrained rats, was resynthesized at approximately the same rate in the two groups of animals (9 and 11 mumol/(g h), but the trained animals were able to achieve this without further depletion of liver glycogen beyond that which had occurred during exercise. In untrained animals liver glycogen concentrations continued to drop for 60 min beyond the end of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)