THE IN VITRO RELEASE OF AMINO ACIDS BY RUMEN PAPILLAE

Rumen papillae from cattle were incubated aerobically with combinations of NH4Cl, amino acids and salts of organic acids, the latter including propionate, pyruvate, α-ketoglutarate and glyoxylate. Amino acids in the incubation media were analyzed using a gas-liquid chromatographic technique entailing separation of the isobutyl-N(0)-heptafluorobutyryl esters: glutamine was recovered with glutamate, asparagine with aspartate, and citrulline with ornithine. Rumen papillae incubated with pyruvate or propionate released alanine, but with the latter substrate only glutamate was effective as a nitrogen source. Glycine and glutamate plus glutamine were released in the presence of glyoxylate and α-ketoglutarate, respectively. Serine and aspartate plus asparagine were not quantitatively major products released by rumen papillae. Glutamate was an effective source of nitrogen for the release of alanine and glycine with pyruvate and glyoxylate, respectively, as carbon sources. When rumen papillae were incubated with pyruvate or glyoxylate as the added carbon source, glutamine nitrogen disappeared and was not accounted for by the amino acids measured. With arginine as a substrate, there was a release of ornithine by rumen papillae indicating urea production. The tissues of rumen papillae appear to synthesize amino acids from expected carbon sources with ammonia or glutamate as nitrogen sources and to catabolize glutamine and arginine. The metabolism of amino acids by rumen papillae would contribute to the interchange of nitrogen between the rumen and the host.