Pyruvate and Propionate Metabolism in Lactating Cows

The glucogenic behavior of butyrate in ruminants has been reported frequently, but the metabolic nature of this anomalous relationship has remained obscure. To test the possibility that the metabolism of butyrate affects gluconeogenesis, lactating cows were given intravenous injections of tracer amounts of pyruvate-2-14C and, in parallel experiments, of pyruvate-2-l% plus substrate amounts of sodium butyrate (0.7 mm per kg of body weight). When butyrate was injected, less 14C appeared in respired COS and more 14C in plasma glucose. The intramolecular labeling pattern in glutamate also changed with butyrate injection, with the result that more of the 14C was located in carbon derived from oxalacetate compared to carbon derived from acetylCoA. These results indicate that butyrate metabolism affects gluconeogenesis by sparing pyruvate oxidation, thereby conserving a glucogenic precursor, and, in addition, by enhancing the conversion of pyruvate to oxalacetate.