The effect of ketone bodies on nitrogen metabolism in skeletal muscle.

1. The ketone bodies, D-beta-hydroxybutyrate and acetoacetate, inhibit glycolysis thereby reducing pyruvate availability which leads to a marked inhibition of branched-chain amino acid metabolism and alanine synthesis in skeletal muscles from fasted mammalian and avian species. 2. The rate of glutamine release from skeletal muscles from fasted birds is increased at the expense of alanine in the presence of elevated concentrations of ketone bodies because of an increase in the availability of glutamate for glutamine synthesis. 3. Ketone bodies inhibit both protein synthesis and protein degradation in skeletal muscles from fasted mammalian and avian species in vitro. The mechanisms involved remain unknown. 4. Inhibition of amino acid metabolism and protein turnover in skeletal muscle by ketone bodies may be an important survival mechanism during adaptation to catabolic states such as prolonged fasting.