Ketogenic regulation by certain metabolites in rumen epithelium

In experiments with rumen epithelium incubated in vitro in the presence of butyrate, the ketogenic effect of glucose was shared by epimeric monosaccharides but not by non-metabolizable analogues. 14C from glucose was not incorporated into ketone bodies. Malate increased ketogenesis from butyrate and decreased its oxidation, pyruvate and NH4+ had the opposite effect, and malonate inhibited both processes. The ketogenic effect of glucose was also effective with isovalerate maintaining the high proportion of acetoacetate which is characteristic of this substrate. Rumen epithelium transformed added acetoacetate into 3-hydroxybutyrate. It is concluded that reducing equivalents produced from glucose and other metabolizable substrates are responsible regulators of ketogenesis from butyrate. The results are discussed in view of the functional role of ruminal ketogenesis.