Metabolism of acetate, propionate and butyrate by sheep-liver slices

Abstract

The metabolism of acetate, propionate and butyrate by sheep-liver slices was studied with C14-labelled substrates. Production of labelled CO2 and incorporation of radioactivity into glucose were followed. Propionate and butyrate were more readily oxidized than acetate, and propionate was incorporated into glucose to a greater extent than were the other substrates. Oxidation of propionate and incorporation into glucose reached a maximum at a propionate concentration of about 6mM. The distribution of radioactivity in glucose isolated after the incubation of liver slices from fed sheep with acetate and propionate labelled at C-1 or C-2 and butyrate labelled at C-l, C-2 or C-3 indicated that propionate could act as a source of glucose, but the incorporation of acetate and butyrate was consistent with entry into glucose as acetyl-coenzyme A through the tricarboxylic acid cycle. The interrelations of acetate, propionate and butyrate were studied. Acetate and butyrate stimulated propionate metabolism by tissues from starved sheep, and propionate and butyrate both inhibited acetate oxidation. Acetate and propionate were without effect on butyrate oxidation, but butyrate incorporation into glucose was augmented in the presence of unlabelled propionate. Increased ketone-body production by liver slices was observed in the presence of acetate and butyrate. The proportion of [beta]-hydroxybutyrate in ketone bodies exceeded 80% in all cases. Attempts to promote glycogen synthesis in liver slices in media containing varying ratios of Na+ ion K+ ion concentration were unsuccessful.