Specific Dynamic Action of Acetic Acid and Heat Increment of Feeding in Ruminants

Abstract

Attention is drawn to the lack of adequate explanation of the phenomena of the high specific dynamic action of acetic acid and the high heat increment of feeding in ruminants. The theory is advanced that the high specific dynamic action of acetic acid is related to the following facts: it is non-glyconeogenic; it is not utilized in protein synthesis; it is oxidized by most, if nor all, tissues; and it is utilized significantly for lipogenesis by only a few tissues, excluding in particular muscle and kidney. Furthermore, the metabolism of the acid appears to be relatively "uncontrolled," the uptake by tissues being directly dependent on the arterial level and unaffected by insulin, at least in ruminants, in contrast to glucose. Finally, there is very little storage of absorbed acetic acid in the body fluids. Consequently, it is metabolized almost as fast as it is absorbed: in some tissues, notably intestinal wall, liver, and adipose tissue and lung, it is partitioned between oxidation and lipogenesis; in others, particularly muscle and kidney, it is of necessity largely utilized oxidatively. The high specific dynamic action of acetic acid indicates that the net partition is in favor of oxidation. The high heat increment of feeding in ruminants is considered as due to the quantitative importance of acetic acid and butyric acid, which also has a high specific dynamic action, as products of ruminal digestion, and of acetic acid and beta-hydroxybutyric acid, derived from acetic and butyric acids, as peripheral metabolites.