Studies on the carbohydrate metabolism of sheep. II. The uptake by the tissues of glucose and acetic acid from the peripheral circulation

Abstract

The level of volatile fatty acid in the peripheral blood of sheep is considerably higher than in non-ruminants, arterial levels reaching 10 mg. per cent. (as acetic acid) or higher. That the level is related to fermentation in the rumen is indicated by its steady decrease during fasting. In sheep fed on rations of widely differing composition, 86-95 per cent. (molar basis) of the total volatile fatty acid in arterial blood was found to be acetic acid. Small amounts of propionic, butyric, and at least one other acid were also present. The removal of acetic acid from the arterial blood during its passage through the tissues of the head is considerable, and the extent of its removal is closely dependent upon its arterial level. There was no evidence that acids other than acetic were removed in significant quantities. The low normal blood-glucose level in fed sheep is associated with a smaller uptake of glucose by the tissues of the sheep than occurs in non-ruminants and this low uptake is compensated by a higher uptake of acetic acid. Arterio-venous differences of glucose and of volatile fatty acid have been measured in two dogs, after feeding and during fasting, and are compared with the results obtained from sheep. These findings are discussed in the light of present knowledge of the influence on ruminant metabolism of the rumen and the digestive processes therein.