Exercise-induced changes in atrial peptides in relation to neuroendocrine responses and fluid balance in the horse.

This research studied the changes in atrial peptides (proteins that affect heart function) due to exercise in horses. It also delved into the understanding of hormonal changes, fluid balance, and their correlation with these peptides post-exercise.

Objective and Methodology

• The study aimed to understand why plasma atrial natriuretic peptides (ANP and NT-ANP), proteins that control blood volume and pressure, remain elevated in horses after exercise. It sought to assess whether these changes are linked to changes in hormonal, neuroendocrine responses and fluid balance.
• The researchers conducted a graded submaximal exercise test on six Finnhorses on a treadmill.
• Throughout the exercise and subsequent recovery period, they measured several parameters including plasma concentrations of ANP, NT-ANP, arginine vasopressin (AVP), adrenocorticotrophin (ACTH), beta-endorphin, cortisol, catecholamines, and indicators of fluid balance such as plasma total protein and electrolytes.

Findings

• Post-exercise, while AVP and catecholamines levels dropped rapidly, atrial peptides, ACTH, beta-endorphin, and cortisol remained high for a more extended period.
• ANP levels were at their peak at the 5-minute mark post-exercise, while NT-ANP peaked 30 minutes after exercise. After 60 minutes, ANP remained significantly increased whereas NT-ANP was even above its exercise-end level.
• A potential reason for the differing patterns between ANP and NT-ANP might be due to the differences in their plasma half-lives (time it takes for the concentration of a substance to reduce to half in the body).
• A continuous increase in NT-ANP post-exercise suggests that exercise stimulates the release of atrial peptides during the recovery phase.
• Cortisol, which remained elevated for a more extended period post-exercise, may have somewhat contributed to the post-exercise elevation of the atrial peptides.
• Parameters like packed cell volume (PCV), a measure of the amount of space in the blood taken up by red blood cells, decreased more slowly than plasma total protein and electrolytes post-exercise. This indicated a slow return of blood volume after exercise.

Conclusion

• The research concluded that the persistent post-exercise increase in plasma atrial peptides in horses is likely due to an elevated central blood volume.
• The study deduced that the role of vasoactive hormones- hormones that affect the diameter of blood vessels and hence blood pressure, in this phenomenon is minimal.