Potassium and lactate uptake by noncontracting tissue during strenuous exercise

Area of Science:

• Equine physiology
• Exercise science
• Metabolic regulation

Background:

• High-intensity exercise increases plasma potassium (K+) and lactate (lac-) due to efflux from active skeletal muscle.
• In human athletes, noncontracting tissues help ameliorate these increases through ion uptake.
• The role of noncontracting tissue uptake in ion regulation during strenuous exercise in horses remains to be fully elucidated.

Purpose of the Study:

• To investigate the hypothesis that noncontracting tissues uptake potassium (K+) and lactate (lac-) in strenuously exercising horses.
• To quantify the arteriovenous differences (a-v)diff for K+ and lac- across active and noncontracting tissues during exercise.

Main Methods:

• Simultaneous blood sampling from the carotid artery (CA), femoral vein (FV), and transverse facial vein (TFV) in 5 unconditioned Standardbred horses.
• Horses performed 4.5 minutes of strenuous treadmill exercise.
• Calculation of arteriovenous differences ((a-v)diff) for plasma [K+] and [lac-] across active (CA-FV) and noncontracting (CA-TFV) tissues.

Main Results:

• Plasma [K+] and [lac-] were significantly higher in femoral vein (FV) and carotid artery (CA) blood compared to transverse facial vein (TFV) blood during exercise.
• The magnitude of the arteriovenous difference ((a-v)diff) for both [K+] and [lac-] increased across both active and noncontracting tissues during exercise.
• The directions of the (a-v)diff across active and noncontracting tissues were opposite, indicating release by active and uptake by noncontracting tissues.

Conclusions:

• Noncontracting tissues in horses demonstrably uptake potassium (K+) and lactate (lac-) during strenuous exercise.
• This uptake contributes to the regulation of plasma ion concentrations during high-intensity exercise in equine athletes.
• Findings support a conserved physiological mechanism for ion homeostasis during exercise across species.