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Effects of High Tryptophan Doses and Two Experimental Rations on the Excretion of Urinary Tryptophan Metabolites in Cattle¹

Department of Animal Sciences, Washington State University, Pullman, Washington 99163

High intraruminal doses of tryptophan cause interstitial pulmonary edema and emphysema in cattle. To determine whether specific urinary Trp metabolites may be associated with the development of the disease in cattle, experiments were conducted to identify urinary tryptophan metabolites in cattle and to determine the effects of experimental ration on the excretion of these metabolites. Cattle were given a high or carrier intraruminal dose of L-tryptophan and DL-tryptophan-¹⁴C (U)-benzene ring and urine was collected until the radioactivity was negligible. Urinary tryptophan metabolites were separated into 16 peaks by ion-exchange chromatography. Kynurenine, tryptophan, hydroxyoxindole derivatives, picolinic acid, acetyltryptophan, indole-3-acetic acid, 5-hydroxy-indole-3-acetic acid, oxindole derivative and indican were identified in urine. A high dose of tryptophan resulted in an increased rate of excretion of indoleacetic acid and 5-hydroxyindole-3-acetic acid in the urine compared with a steer given a carrier dose. The percentage of the dose as tryptophan, kynurenine, acetyltryptophan, 5-hydroxyindole-3-acetic acid and indican in the urine was higher in the steer given the high dose. Two steers were fed a concentrate ration and three steers were fed low quality hay for at least 4 weeks prior to tryptophan dosing and urine collection. Cattle fed the concentrate ration excreted more kynurenine and acetyltryptophan than cattle fed hay, but 5-hydroxyindole-3-acetic acid was absent in the urine of these cattle. Cattle fed hay excreted higher amounts of 5-hydroxyindole-3-acetic acid, hydroxyoxindole derivatives and two unidentified metabolites. The data indicate that the experimental ration alters the urinary excretion pattern of tryptophan metabolites in cattle. The results also demonstrate the importance of pathways of tryptophan degradation resulting in the excretion of indole or oxindole derivatives in cattle and the minimal excretion of products derived from the kynurenine pathway.

KEY WORDS: • tryptophan metabolism • indoles • cattle • ionexchange chromatography • urine • emphysema

¹ Supported in part by Public Health Service Research Grant no. HL13645 from the National Heart and Lung Institute. Scientific Paper no. 3848, College of Agriculture, Washington State University, Projects 1893, 1899.

Manuscript received 21 April 1972.