Exercise-Induced Increase in the Capacity of Rat Skeletal Muscle to Oxidize Ketones

Abstract

During and after strenuous prolonged exercise, sedentary individuals develop high blood levels of acetoacetate and β-hydroxybutyrate whereas exercise-trained animals and human subjects do not. We have investigated the possibility that exercise training can increase the capacity of skeletal muscle to oxidize ketones. In this study we measured rates of d-β-[3-¹⁴C]-hydroxybutyrate and [3-¹⁴C]acetoacetate oxidation, and the levels of activity of the enzymes involved in the oxidation of ketones in homogenates of gastrocnemius muscles of exercise-trained and of untrained male rats. The trained animals had markedly lower blood ketone levels immediately and 60 min after a 90 min long bout of exercise than did the sedentary animals. The rates of D-β-[3-¹⁴C]hydroxybutyrate and [3-¹⁴C]acetoacetate oxidation were twice as high in homogenates of muscles from the trained as compared to the sedentary rats. The increases in levels of activity in gastrocnemius muscle in response to the exercise program were: β-hydroxybutyrate dehydrogenase threefold; 3-ketoacid CoA-transferase twofold; and acetoacetyl-CoA thiolase 55%. This exercise-induced increase in the capacity of skeletal muscle to oxidize ketones could play a role in preventing development of ketosis in the physically trained animal during and following prolonged strenuous exercise.