Acetate supply and utilization by the tissues of sheep in vivo

Abstract

1. The supply and utilisation of acetate has been estimated simultaneously in the whole animal and tissues of sheep using a combination of isotope-dilution and arteriovenous-difference techniques. Animals were made alloxandiabetic and acetate metabolism was compared when stabilized to normal metabolite levels with insulin (ITA sheep) and when food and insulin had been withdrawn for 36 h (fasted, diabetic sheep).2. Acetate was simultaneously produced and utilized by all tissues. The exogenous (or gut) supply of acetate was the most important determinant of circulating acetate level. Endogenous acetate was produced mainly in the liver; 77 and 94% in fasted, diabetic and ITA sheep respectively. The production of endogenous acetate remained fairly constant and was not related to ketogenesis, which supports the idea that circulating acetate is largely a product of fermentation. The liver, gut and muscle utilized 17, 25 and 54% respectively (96% total) of the acetate entry rate in ITA sheep; a similar percentage utilization was found in fasted, diabetic sheep.3. Acetate is largely oxidized to carbon dioxide in the gut and muscles of sheep and may account for 30–40% of their oxidative metabolism. This figure is similar to that for the whole animal. The total acetate taken up by the liver could account for 30% of the oxygen consumption; however, the liver may not directly oxidize all the utilized acetate.4. The over-all conclusion from this study is that acetate is largely of dietary origin and the major factor determining its rate of utilization is the arterial concentration.