Castor-oil induced diarrhoea in ponies: a model for acute colitis.

The research established a reliable model for studying acute colitis through inducing the condition in ponies with castor oil. It detailed the progression of the symptoms, the recovery process, and backings from morphological and laboratory tests, also suggesting similarities with certain naturally occurring colitis syndromes in horses.

Introduction and Methodology

• The researchers explored a model for acute colitis by inducing the condition in ponies using castor oil.
• Each pony was given a dosage of 2.5 ml/kg bodyweight of castor oil orally. The symptoms and developments were observed closely.
• Periodic tests were run, focusing on both morphological changes and in vitro transport studies for the times post-induction of colitis at 24, 48, and 72 hours.

Observations and Findings

• Abdominal pain, fever, watery diarrhoea, dehydration, hypovolaemia, toxaemia, and leucopenia were presented, along with a decrease in serum Cl, Na and K levels and metabolic acidosis. These symptoms were the most severe between 24 and 48 hours following the induction of colitis.
• Typically, the condition stabilised after 72 hours, but diarrhoea could persist beyond 96 hours.
• Morphological changes were noted in the caecum and colon, with disruption and exfoliation of the surface epithelium from the basement membrane between 24 and 48 hours. Signs of recovery were observable by 72 hours with the replacement of denuded areas with columnar epithelium.
• The crypt epithelium was consistently unaffected throughout the intestinal tract.
• In vitro transport studies corroborated these findings, showing decreased Na-Cl absorption and normal Cl secretion, indicating an impaired surface epithelium but an intact cryptal epithelium.
• Increased mucosal permeability was evidenced by high ionic conductance and large unidirectional isotopic fluxes.
• During in vitro incubation, tissue conductance improved, implying epithelial repair after the removal of the castor oil.

Conclusions

• As diarrhoea ensued, changes in the population and proportion of bacteria in the faeces were confirmed at necropsy, with E.coli and Enterobacter/Klebsiella sp predominantly present in the large bowel.
• The castor oil-induced colitis model revealed many similarities with intestinal endotoxaemia and secretory-type diarrhoea found in naturally occurring acute colitis syndromes in horses.
• Therefore, this model could be useful for studying the pathophysiological mechanisms that precipitate such critical disorders.