Formation of ketone bodies from [¹⁴C]palmitate and [¹⁴C]glycerol by tissues from ketotic sheep

Labelled ketone bodies were produced readily from [U−¹⁴C]palmitate, [2−¹⁴C]palmitate and [1−¹⁴C]glycerol by sheep rumen-epithelial and liver tissues in vitro. On a tissue-nitrogen basis, both tissues had similar capacities for ketogenesis. Palmitate was a ketogenic substrate in both rumen-epithelial tissue and liver, and more of its ¹⁴C appeared in ketone bodies than in the ¹⁴CO₂ liberated. Glycerol was actively metabolized to ketone bodies, but more readily underwent complete oxidation to carbon dioxide; this complete oxidation was most pronounced in rumen-epithelial tissue from ketotic ewes. These experiments with labelled compounds confirm earlier observations that rumen-epithelial tissue, like liver, actively forms ketone bodies from long-chain fatty acids and show further that normal rumen-epithelial tissue can convert palmitate into ketone bodies as readily as into carbon dioxide. Free glycerol, which is metabolized only by liver tissue in non-ruminants, is also metabolized by rumen epithelium. The rumen epithelium thus has unique metabolic capacity among extrahepatic tissues.