Hepatic and pulmonary enzyme activities in horses.

This research examines the activities of particular enzymes in the lung and liver tissues of horses of varying ages to understand the capacity of these organs to metabolize foreign substances.

Study Design

• The researchers started by working with lung and liver tissues taken from 22 horses that were between 4 months to 32 years old.
• The team produced enzymes such as cytochrome P450 monooxygenases, glutathione S-transferase and soluble epoxide hydrolase from these tissues.
• They used high-performance liquid chromatography to determine the enzyme metabolism rates of substances like ethoxyresorufin, pentoxyresorufin, and naphthalene found in the microsomal enzymes.
• Using spectrophotometry, they detected the activities of glutathione S-transferase and soluble epoxide hydrolase.
• The cytochrome P450 content was then found via the carbon monoxide bound-difference spectrum of dithionite-reduced microsomes.
• Finally, enzyme activity was examined in relation to total protein concentration.

Findings

• Microsomal protein and cytochrome P450 contents were found in all examined horses and didn’t show variations with age.
• All horses showed liver metabolism of ethoxyresorufin, while metabolism of ethoxyresorufin in the lungs and pentoxyresorufin metabolism in both lungs and liver were found to occur at a slower pace.
• Rate of liver naphthalene metabolism did not change with age of the horse but the rate of lung naphthalene metabolism was noteworthy and significantly lower in younger horses (weanlings) between 4 to 6 months old compared to adult horses.
• Hepatic glutathione S-transferase activity (located in cytosol) increased as horses aged but the rate of increase was not significantly high. The lungs of weanlings, however, registered significantly lower activity of glutathione S-transferase than adult horses.
• Finally, both the lungs and liver showed no age-related variations in activity when it came to the enzyme soluble epoxide hydrolase.

Conclusions

• Based on the gathered results, the researchers concluded that the cytochrome P450 isoforms in the lungs, which help to metabolize naphthalene, and lung-based glutathione S-transferases show significantly lower activity in weanlings compared to adult horses.
• This suggests that younger horses might have a reduced ability to metabolize certain toxic substances, known as xenobiotics, compared to their older counterparts due to a lower enzyme activity in their lungs.