3-methylindole-induced pulmonary toxicosis in ponies.

The research focused on understanding the effect of the chemical compound 3-methylindole on the respiratory system of ponies. The study showed changes in the respiratory rate, blood gas levels, lung volumes, and other related variables after the oral administration of 3-methylindole in ponies.

Research Method

1. The researchers used unanesthetized ponies as subjects for the study.
2. These ponies were given either 500 ml of corn oil alone, or 100 mg of 3-methylindole (3MI) per kg of their body weight, mixed with 500 ml of corn oil.
3. The arterial blood gas tensions, pulmonary mechanics, and lung volumes in the subjects were measured before and 24 to 48 hours after the administration.

Results and Observations

1. The research found that the respiratory rate and minute ventilation in the ponies were increased by the 3MI treatment.
2. The researchers also discovered that these increased rates decreased after bilateral cervical vagotomy, a surgery in which the <a href="/equine-cranial-nerve-anatomy/" title="Cranial Nerves in Horses: Role in Sight, Hearing, Chewing & Balance”>vagus nerve is cut. This suggests that the increase in respiratory rate induced by 3MI was mediated by the vagus nerve.
3. Arterial O2 tension remained unaffected while the arterial CO2 tension decreased below baseline after the administration of 3MI and the vagotomy.
4. 3MI also resulted in a decrease in specific respiratory conductance and dynamic compliance. However, after the vagotomy, the specific conductance increased again.
5. The functional residual capacity, the volume of air remaining in the lungs after a normal exhalation, increased after 3MI treatment but was unaffected by the vagotomy.
6. The total lung capacity and quasistatic compliance, the change in lung volume for each unit change in pressure, were not affected by either treatment.
7. The minimal volume of lungs, the volume left after a maximal exhalation, was found to be larger in 3MI-treated ponies compared to untreated ones.

Conclusions

1. The decreased dynamic compliance and specific respiratory conductance, along with the increased functional residual capacity and minimal volume, are all indicative of small airway obstruction.
2. The research indicates these conditions were a result of necrotizing bronchiolitis and bronchiolar obstruction, both of which were observed histologically in 3MI-treated ponies.