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

The research evaluated the impact of orally administered L-tryptophan and indoleactic acid, and intravenously administered L-tryptophan in ponies, focusing specifically on its hematologic and pathologic effects.

Study Design and Grouping

• The experiment involved 16 adult Shetland ponies divided into four groups.
• Group 1 (five ponies) were given 0.6 g of tryptophan/kg of body weight in a water slurry administered through a stomach tube.
• Group 2 (four ponies) were given 0.35 g of tryptophan/kg orally.
• Group 3 (four ponies) were given 0.35 g of indoleacetic acid/kg orally.
• Group 4 (three ponies) were administered a single 4-hour intravenous infusion of 0.1 g of tryptophan/kg.

Observations and Findings

• Four out of five ponies in Group 1 developed symptoms including restlessness, an increased respiratory rate, hemolysis, and hemoglobinuria.
• Only one pony in Group 2 experienced hemolysis, hemoglobinuria, and a significant increase in respiratory rate.
• Renal pathologic lesions, consistent with hemoglobinuric nephrosis, were observed in four of the nine ponies given tryptophan orally.
• Bronchiolar degeneration was noted in four out of the nine ponies that received tryptophan orally—though the relevance of these respiratory lesions was not discerned.
• Ponies in Groups 3 and 4 exhibited no clinical or pathological abnormalities.
• Plasma tryptophan levels rose significantly in Groups 1 and 2 at 6 hours after dosing, with a second peak at 12 hours, and returned to predose values by 48 hours.
• Only two ponies had detectable plasma indole and 3-methylindole concentrations.

Metabolism Study

• Incubation of cecal fluid from three ponies resulted in percentage conversion of tryptophan to indole between 5.84% to 16.75%, favoring an assertion that indole was the major metabolite of orally administered tryptophan in these ponies.
• No 3-Methylindole was produced.

The research thus indicated certain hematologic and pathologic reactions to oral administration of L-tryptophan in ponies. These findings contribute to a better understanding of the physiological response to this amino acid, its metabolism, and underlying metabolic pathways, leading to potentially improved treatment approaches where such administration is involved.