Effects of Reduced Phenolic Acids on Ruminant Hepatic Metabolism

Previous work has shown that ruminants absorb and metabolize large amounts of aromatic acid compounds. A major source of these compounds probably is derived from dietary phenolic monomers. Reduced forms of phenolic monomers have been identified previously in ruminal fluid. The effects of four reduced phenolics, benzoic (BA), 3-phenylpropionic (PPA), trans-cinnamic (CA), and 3-(4-hydroxyphenyl)propionic (4OHPPA) acids on bovine liver tissue and ovine hepatocyte metabolism in vitro were investigated. All the reduced phenolics inhibited gluconeogenesis from propionate in bovine liver tissue at.4 mM and BA, PPA, and CA inhibited it at.2 mM. Oxidation of palmitate was inhibited by all the reduced phenolics (.2 mM) with 4OHPPA being least inhibitory. The reduced phenolics caused leakage of lactate dehydrogenase from bovine liver tissue suggesting that irreversible cell membrane damage occurred. Reduced phenolics inhibited gluconeogenesis from propionate in ovine hepatocytes at the lowest concentration (50 {μ}M) thus far observed in ruminants. There was a linear relationship between glycine concentration in the incubation medium and alleviation of inhibition of gluconeogenesis from propionate and hippuric acid (HA) production. This, combined with the observation that HA (1.2 mM) did not inhibit gluconeogenesis from propionate, suggests that the alleviation is the result of conversion of the reduced phenolics to HA and that glycine concentration limited HA production. Bovine serum albumin failed to alleviate inhibition of gluconeogenesis from propionate. Concentrations of BA, PPA, CA, and 4OHPPA in hepatic portal venous blood from wethers fed grass hays ad libitum ranged from 1.11 to 2.39, 7.00 to 19.06,.03 to.05, and less than.62 {μ}M, respectively. Wethers fed alfalfa hay had net uptake of PPA from portal-drained viscera which was subsequently removed by liver. Uptakes of BA and PPA by the splanchnic bed approximated HA release, suggesting that liver converts BA and PPA to HA. Net splanchnic uptake of BA implies extra-splanchnic production of BA. Net fluxes of CA and 4OHPPA were less than 2 μmol/h. 3-Phenylpropionic acid had the greatest concentration in hepatic portal venous blood and the greatest ability to inhibit gluconeogenesis from propionate in ovine hepatocytes, suggesting that it could inhibit hepatic gluconeogenesis from propionate in vivo.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Animal Science

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Cremin, John Daniel, Jr.

Contributors dc:contributor

• Fahey, George C., Jr.

• Agriculture, Animal Culture and Nutrition

Identifier

(UMI)AAI9503172

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/72219