Influence of training on plasma adrenaline and noradrenaline kinetics in untrained Standardbreds

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Reasons for performing study:

Catecholamines (CAT) play an important role in modulating the response to exercise. But the kinetics of CAT changes during exercise are difficult to study due to their short biological half-life.


Learning about variations in plasma CAT levels during training could furnish new information regarding sweating, redistribution of blood flow and energy metabolism.


Four untrained Standardbreds, adapted to treadmill work, were used to determine the influence of training on plasma adrenaline (A) and noradrenaline (NA) kinetics. Horses underwent a standardised exercise test (SET) on treadmill before (SET1), and 1 (SET2) and 2 months after (SET3) the start of a moderate training period on treadmill. The SET procedure was: warm-up and a single step of 2 min at 200 beats/min heart rate (SS). The automatic blood collection system (that has been carried out during SS) and the preparation of the horses have been described previously. The system was programmed to obtain a blood sample every 15 sec (8 blood samples per SS). Analyses were performed by HPLC. Training progress was monitored by means of anaerobic threshold velocity (V4) and the velocity during SS (V200). Wilcoxon's test was used for statistical analysis.


Decreased levels of A and NA with significant differences between SET1/SET2 and SET1/SET3 for A (P = 0.007) and NA (P = 0.007) were found. There were no differences between SET2 and SET3 for A (P= 0.195) and NA (P = 0.054).


Training appears to influence the level of plasma CAT and this influence is greater during the first training period in untrained Standardbreds.

Potential relevance:

It may prove interesting to associate the study of training-induced modifications of the concentration of plasma CAT with thermoregulation, which is under catecholaminergic control and undergoes important adaptations during training.

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