Effect of exercise on enzymatic activity in tracheal fluid and on intrapleural pressure difference in horses

Seventeen trotters, eight healthy and nine with a mild respiratory disease, underwent a submaximal treadmill exercise. Heart rate, breathing frequency, intrapleural pressure difference (IP difference) as well as haematocrit and concentration of lactic acid in blood were monitored before exercise, during exercise and during recovery. The activities of beta-glucuronidase and plasmin, total proteolytic activity and trypsin inhibitory capacity were measured from the tracheal fluid before and after exercise. IP difference significantly increased during exercise and returned to normal values within 15 min in healthy horses. Differences in intrapleural pressure between healthy and diseased horses were not significant during exercise. Increase of the respiratory rate was monitored during recovery probably due to respiratory compensation of the lactic acidosis. Activities of beta-glucuronidase increased and activities of plasmin and trypsin inhibitory capacity decreased due to exercise. Most prominent changes were seen in the decrease of plasmin activity. The total proteolytic activity in the tracheal fluid before exercise correlated with the VLa4 values, indicating that a mild respiratory disease, which causes proteolysis in the respiratory tract, decreases performance capacity of the horse.