Acute hemolytic anemia induced by oral administration of indole in ponies.

The research article investigates how the oral ingestion of indole, a tryptophan metabolite, leads to acute intravascular hemolysis – a condition where red blood cells are destroyed – in ponies.

Study Design and Procedure

• The researchers divided eight ponies into two groups: group 1, which was given 0.2g of indole/kg of body weight, and group 2, which was given half of that dose – 0.1g of indole/kg.
• After administering the indole, the researchers carried out a number of physical, hematologic, and physiological tests to study the effects of the indole administration.

Observed Effects of Indole

• Within 24 hours of ingestion, intravascular hemolysis – the destruction of red blood cells within the bloodstream – and hemoglobinuria – the presence of free hemoglobin in the urine – were detected in both groups.
• This hemolysis was indicated by a reduction in packed cell volume (PCV), hemoglobin concentration, and red blood cell (RBC) count, along with an increased concentration of indirect bilirubin.
• At the same time, erythrocyte, or red blood cell, fragility increased for ponies in both groups. This fragility peaked at 16 hours post-indole ingestion, then reduced below pre-dose levels at 72 hours after dosing.

Further Observations and Results

• Indole concentrations in the plasma increased significantly in both groups from the nondetectable predose levels.
• In group 1, the concentration of indole was 203% that of group 2. Detectable concentrations of plasma indole continued to be present 24 hours after dosing in group 1 ponies, whereas plasma indole levels in group 2 ponies had returned to nondetectable levels by 12 hours.
• By 72 hours post-indole administration, all ponies in group 1 had either died or had to be euthanized, while group 2 ponies were euthanized between 48 and 120 hours.
• At necropsy (animal autopsy), all body fat, mucous membranes, and elastic tissue were observed to be stained yellow. Hemoglobinuric nephrosis – kidney damage caused by hemoglobin in the urine – was the most prominent microscopic lesion found.

Conclusion

• The study reveals that indole, a metabolite derived from the amino acid tryptophan, induces acute intravascular hemolysis in ponies. This condition is clearly linked to the doses of indole administered, and manifested as a series of physiological issues, leading to the deaths of the ponies.