Plasma concentrations of cortisol and corticosterone in the normal horse.

This paper is about the establishment of the average plasma levels of cortisol and corticosterone in horses under normal conditions, as well as the impacts of external influences like corticotropin and dexamethasone.

Objective of the Research

• The research primarily aimed to establish the normal plasma levels of cortisol and corticosterone in horses. It further set out to investigate whether these levels differed according to variables such as age, sex, and pregnancy.

Method and Findings

• The researchers employed a method called competitive protein-binding analysis or radiostereoassay to measure the average concentration of cortisol and corticosterone in horse plasma. They found that the mean plasma concentration was 5.12 μg./ml., with a standard deviation of 1.67 μg.
• The study discovered that there were no significant variations in these levels according to factors such as the horse’s age, sex, or pregnancy. This suggests that these particular variables do not substantially influence the plasma concentration of cortisol and corticosterone in horses.
• The researchers identified that there might be diurnal variations in the hormone levels. Observation revealed high values in the morning that gradually decreased towards evening. This could suggest that horses, like humans, share a similar circadian rhythm in cortisol activity.

Impact of External Influences

• The research also explored the impacts of external substances on the horse’s plasma levels of cortisol and corticosterone. When horses were given corticotropin (also known as acth), an increase in these levels was observed, implying that corticotropin can bring about an elevation in cortisol and corticosterone concentration in a horse’s bloodstream.
• Conversely, when dexamethasone was administered to the horses, a decrease in the plasma levels of the two steroids was noted, suggesting dexamethasone can suppress cortisol and corticosterone production in horses.

Conclusion

• Providing valuable norms for the equine medical community, this research accurately determined the usual range of cortisol and corticosterone concentration in horse plasma. The discovery of the influence of medication, diurnal cycle, and the lack of significant variation due to age, sex, or pregnancy can help vets better understand and diagnose equine illnesses related to these hormones.