Acute hemolytic anemia after oral administration of L-tryptophan in ponies

• Published in: American journal of veterinary research Vol. 52; no. 5; p. 742
• Main Authors: Paradis, M R, Breeze, R G, Bayly, W M, Counts, D F, Laegreid, W W
• Format: Journal Article
• Language: English
• Published: United States 01-05-1991
• Subjects: Acute Disease; Administration, Oral; Anemia, Hemolytic - chemically induced; Anemia, Hemolytic - veterinary; Animals; Female; Hematocrit - veterinary; Hemoglobinuria - chemically induced; Hemoglobinuria - veterinary; Hemolysis - drug effects; Horse Diseases - chemically induced; Horses; Indoleacetic Acids - administration & dosage; Indoleacetic Acids - metabolism; Indoleacetic Acids - toxicity; Indoles - metabolism; Kidney - drug effects; Lung - drug effects; Male; Motor Activity - drug effects; Respiration - drug effects; Skatole - metabolism; Tryptophan - administration & dosage; Tryptophan - metabolism; Tryptophan - toxicity
• ISSN: 0002-9645
• DOI: 10.2460/ajvr.1991.52.05.742

The hematologic and pathologic effects of orally administered L-tryptophan and indoleactic acid and of L-tryptophan administered IV were studied in ponies. Sixteen adult Shetland ponies were allotted into 4 experimental groups. Group 1 consisted of 5 ponies (1-5) given 0.6 g of tryptophan/kg of body weight in a water slurry via stomach tube. Group 2 included 4 ponies (6-9) given 0.35 g of tryptophan/kg orally. Group-3 ponies (10-13) were given 0.35 g of indoleacetic acid/kg orally. Group 4 consisted of 3 ponies (14-16) given a single 4-hour IV infusion of 0.1 g of tryptophan/kg. Restlessness, increased respiratory rate, hemolysis, and hemoglobinuria were detected in 4 of the 5 group-1 ponies. Only pony 7 in group 2 developed hemolysis, hemoglobinuria, and a significant increase in respiratory rate. Renal pathologic lesions, consistent with hemoglobinuric nephrosis, were seen in ponies 2, 4, 5, and 7. Bronchiolar degeneration was evident in 4 of 9 ponies given tryptophan orally. The importance of these respiratory lesions was unknown. Clinical or pathologic abnormalities were not noticed in the ponies of groups 3 and 4. Mean plasma tryptophan values increased significantly in groups 1 and 2 at 6 hours after dosing. A second peak of tryptophan was detected in both groups at 12 hours. Values returned to predose values by 48 hours. Plasma indole and 3-methylindole concentrations were detectable in only 2 ponies (4 and 7). In vitro incubations of cecal fluid from ponies 6, 8, and 9 yielded a percentage conversion of tryptophan to indole of 16.75%, 5.84%, and 7.96%, respectively. 3-Methylindole was not produced. These results suggested that indole was the major metabolite of orally administered tryptophan in these ponies.