Utilization of volatile fatty acids in ruminants II. Comparison of the metabolism of acetate, propionate and butyrate when injected into the jugular vein, portal vein or the rumen

Abstract

[1- 14C]Acetate, [1- 14C]propionate and [1- 14C]butyrate were administered to sheep and goats via the jugular vein, portal vein or added directly into the rumen in order to study the effect of route of administration on transfer of 14C to liver glycogen and various blood substrates. The data show that the extent to which 14C from [1- 14C]-acetate, [1- 14C]propionate or [1- 14C]butyrate is incorporated into blood glucose or liver glycogen depends on whether the acids are injected into the jugular vein or portal vein or added to the rumen. The work demonstrates that a tracer dose of [ 14C]butyrate injected into the jugular vein labels blood glucose more than [ 14C]acetate because of the higher specific activity of blood butyrate. When unlabeled butyrate is administered along with a tracer dose of [1- 14C]butyrate the specific activity of blood glucose is similar to that observed when acetate is administered. This glucogenic effect of butyrate that has been observed many times is an anomaly and is explained by the fact that a tracer dose of [1- 14C]butyrate injected into the jugular vein is not diluted with unlabeled butyrate because butyrate is not normally present in peripheral blood.