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Plasma hypoxanthine and ammonia in humans during prolonged exercise
K Sahlin1, M Tonkonogi, K Söderlund
1Department of Physiology and Pharmacology, Box 5626, Karolinska Institute, Stockholm University College of Physical Education and Sports, S-11486 Stockholm, Sweden. kent.sahlin@fyfa.ki.se
European Journal of Applied Physiology and Occupational Physiology
|September 29, 1999
Summary
Plasma hypoxanthine (Hx) levels rise during prolonged cycling, indicating adenine nucleotide breakdown and energetic stress. Higher Hx levels correlate with reduced endurance, suggesting its potential as a marker for training status and overtraining.
Area of Science:
- Exercise Physiology
- Biochemistry
- Sports Science
Background:
- Oxypurines, including hypoxanthine (Hx), xanthine, and urate, are involved in cellular energy metabolism.
- Understanding plasma oxypurine dynamics during exercise can provide insights into metabolic stress and fatigue.
- Prolonged moderate-intensity exercise presents a model to study these biochemical changes.
Purpose of the Study:
- To investigate the time course of plasma oxypurine concentrations during prolonged cycling exercise to fatigue.
- To examine the relationship between plasma hypoxanthine levels and muscle adenine nucleotide metabolism.
- To assess the correlation of plasma hypoxanthine with other metabolic markers and endurance capacity.
Main Methods:
- Ten subjects performed prolonged cycling at 74% of VO2(max) until fatigue.
- Plasma concentrations of hypoxanthine, xanthine, and urate were measured.
- Muscle adenine nucleotide (ATP, ADP, AMP) and inosine monophosphate (IMP) content were analyzed pre- and post-exercise in a subset of subjects.
Main Results:
- Plasma oxypurine levels increased during exercise, with significant inter-individual variability.
- Plasma hypoxanthine ([Hx]) showed an eight-fold increase from rest to fatigue.
- Higher post-exercise plasma [Hx] correlated with decreased muscle total adenine nucleotides (TAN) and increased IMP, alongside elevated plasma ammonia and blood lactate.
Conclusions:
- Plasma hypoxanthine increases during moderate-intensity exercise, reflecting adenine nucleotide degradation and energetic stress.
- Plasma [Hx] demonstrates considerable inter-individual variation during prolonged exercise.
- Plasma [Hx] shows potential as a biomarker for assessing exercise-induced metabolic stress, training status, and overtraining.