The origin of urinary aromatic compounds excreted by ruminants

Abstract

1. Dietary phenolic cinnamic acids are hydrogenated in the side-chain, demethylated and dehydroxylated in the rumen and are responsible for the large urinary output of benzoic acid by ruminants.2. Decarboxylation of phenolic acids to simple phenols is another reaction of the intestinal microflora and experiments were made to determine the extent of this reaction in the rumen of sheep.3. In five experiments phenolic compounds, quinic acid or casein were infused into therumen or abomasum of sheep and increments in urinary outputs of phenolic acids and phenols determined by thin-layer and gas-liquid chromatography.4. Production of phenols was almost exclusively confined to reactions in the rumen.5. Rumen administration of phenolic benzoic or phenylacetic acids which contained a 4-hydroxy substituent yielded large increments in urinary phenol outputs. Other phenolic benzoic and phenylacetic acids were not decarboxytated. Rumen decarboxylation of 4-hydroxy-3-phenylpropionic acid did not occur and decarboxylation of 4-hydroxycinnamic acids was slight.6. Nearly half the tyrosine content of rumen-administered casein was excreted asp-cresol, a decarboxylation product of 4-hydroxyphenylaceticacid,p-Cresol was the principal phenol found in sheepurine.7. Catechol and phenol were consistently found in sheep urine samples andp-ethylphenol, resorcinol, quinol, 4-methylcatechol, orcinoland pyrogallol were also found when suitable precursors were infused to the rumen.8. It is concluded thatp-cresol is a rumen metabolite of tyrosine. The other phenols found are microbial metabolites of phenolic precursorswhich are either widely distributed in plants such as 4-hydroxybenzoic, protocatechuic andvanillic acids or of more limited distribution such as the orcinol glycosides of some Ericaceous plants.