Recent developments in ketone-body metabolism.

There is now no doubt that ketone bodies (acetoacetate and D-3-hydroxybutyrate) are important oxidizable substrates for peripheral tissues, especially the brain. Although oxidation is the major fate of ketone bodies, more recent evidence suggests that ketone bodies can act as lipogenic substrates in certain tissues, notably the developing brain and the lactating mammary gland. Apart from their roles as respiratory fuels or lipogenic substrates, i t is now clear that the concentrations of ketone bodies in the circulation can act as ‘signals’ to control their own formation (via effects on adipose-tissue lipolysis) and t o regulate the supply of glucose precursors (glycerol, alanine and lactate). The aim of this contribution is to review the new information on ketone-body metabolism that has accumulated over the last 5 years and to emphasize the areas where further work is required. The specific areas covered here are the short-term intrahepatic regulation of ketogenesis, ketone bodies as Iipogenic precursors and as regulators of substrate supply t o the liver. It is not the intention to discuss in detail the literature before 1970 nor to deal with ketone-body metabolism in ruminants, which has recently been reviewed (Baird, 1977). For a more comprehensive treatment of the subject the reader should consult the following reviews: McGarry & Foster (1977), Williamson & Whitelaw (19786) and Robinson & Williamson (1979).