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Inhibition of Ruminal Degradation of L-Tryptophan to 3-Methylindole, in Vitro¹

Washington State University², Pullman 99164

Abstract

Available evidence supports the view that acute bovine pulmonary edema and emphysema (ABPE) is related to ruminal production of 3-methylindole (3MI) from L-tryptophan (TRP). Ruminal production of 3 MI is a two-step process involving the conversion of TRP to indoleacetic acid (IAA) followed by decarboxylation of IAA and 3MI. Reduction in ruminal 3MI production by the inhibition of either of these processes may prevent the onset of ABPE. A closed-system, in vitro ruminal fermentation technique was used to screen 27 compounds for their ability to reduce the conversion of TRP to 3 MI. Several compounds tended to reduce 3MI production at both 25 and 5 µg/ml. Desoxysalinomycin, X-206, chloral hydrate, nigericin, lasalocid, monensin, narasin and salinomycin all reduced 3MI production by more than 80% at 5 µg/ml without reducing total VFA production. All of these compounds, except chloral hydrate, are polyether antibiotics. At least part of the inhibition due to monensin and narasin occurs at the level of TRP conversion to IAA.

¹ Scientific Paper 5454. College of Agriculture Research Center, Washington State Univ. Supported in part by NIH Grant No. HL-13645 and the Dept. of Anim. Sci., WSU Project 1893.

² Dept. of Anim. Sci.