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Plasma ammonia and lactate responses using incremental and constant speed exercise tests.
R C Harris1, D B Harris, M Dunnett
1Exercise Research Group (E.R.G.), Royal Veterinary College, University of London, Hatfield, UK.
Equine Veterinary Journal. Supplement
|February 5, 2000
Summary
Plasma ammonia (NH3) accumulation during intense exercise can be measured using incremental or constant speed protocols. Both methods revealed distinct thresholds for NH3 onset in horses, highlighting the practicality of these exercise tests.
Area of Science:
- Exercise Physiology
- Biochemistry
Background:
- Plasma ammonia (NH3) is produced during intense exercise, primarily from adenosine monophosphate (AMP) deamination in muscles.
- Exercise-induced NH3 formation is influenced by muscle fiber recruitment and intracellular factors affecting adenosine diphosphate (ADP) homeostasis.
Purpose of the Study:
- To compare incremental and constant speed exercise protocols for investigating plasma NH3 accumulation during intense exercise in horses.
- To assess the practicality of measuring NH3 concentration curves during different exercise intensities.
Main Methods:
- Six trained Thoroughbred horses performed a step-wise incremental treadmill test and a constant-speed maximum-exercise tolerance test.
- Blood samples were collected at 20-second intervals to measure plasma NH3 and lactate levels during both protocols.
Main Results:
- Significant inter- and intra-horse variability was observed in time-dependent lactate and NH3 responses.
- A distinct threshold for plasma NH3 accumulation was identified in 3 out of 6 horses during incremental exercise.
- Thresholds for NH3 onset were also observed in 5 out of 6 horses during constant-speed exercise.
Conclusions:
- Measuring plasma NH3 concentration curves is practical, even during short incremental tests.
- Incremental exercise tests offer the advantage of simultaneous measurement of cardiovascular and respiratory functions alongside NH3 levels.