Ultrastructural observations in ponies after treatment with monensin.

The research studied the effects of acute monensin poisoning in ponies. The study looked at the physical changes in a pony’s heart, diaphragm, muscle, liver, and kidney after administering monensin, and found that heart mitochondria are primarily affected.

Experimental Approach

• This study used ultrastructural studies, which are investigations at a microscopic level, to examine changes in the ponies’ hearts, diaphragms, muscles, livers and kidneys.
• The researchers administered a single oral dose of monensin to each of the three ponies in the experiment. The dose was equivalent to 4 mg/kg of the ponies’ body weight.
• The ponies were monitored and observed to develop severe signs of toxicosis, which is an extreme response to toxins. Given the severity of their symptoms, the ponies were euthanized between 28 to 72 hours after treatment for examination.

Research Findings

• The research primarily found substantial damage in the myocardium (heart muscle tissue) of two of the three ponies. Specifically, the mitochondria within these tissues were notably swollen, and lipoidosis (an overabundance of fat) was observed. This shows that the mitochondria of the heart muscle are particularly susceptible to monensin poisoning.
• The third pony also showed similar signs of mitochondrial swelling and lipoidosis, but these changes were less severe compared to the other two ponies.
• Microscopic examination of the liver cells (hepatocytes) of the three ponies also found physical changes, including an increase in the amount of smooth endoplasmic reticulum (a cellular structure involved in protein and lipid synthesis), a substantial increase in lipid droplets and vacuoles (small cavities in the cell often containing fluid), a twofold increase in the number of peroxisomes per cell (small cellular components involved in various metabolic processes), and the presence of a membrane-bound protein-like body within some hepatocytes.

Conclusion

• The findings of the study indicate that monensin poisoning in ponies primarily targets the mitochondria in the heart. The observed changes in other tissues like the liver also suggest the extensive systemic effects of this poison.
• The ultrastructural observations in this research provides valuable insights into the potentially fatal physiological responses to monensin toxicity in ponies, thus highlighting the need for careful usage and monitoring of such substances.