The effect of β‐adrenergic blockade on the recovery process after strenuous exercise in the rainbow trout, Salmo gairdneri Richardson

Trout fitted with arterial catheters were subjected to 6 min of strenuous exercise, injected with either saline (controls) or the β‐adrenergic antagonist propranolol, and monitored over the following 8‐h recovery period. Control responses were very similar to those previously reported, except for much higher resting and post‐exercise plasma catecholamine levels, and less marked RBC pHi regulation, perhaps due to season (February–May). Trout subjected to prior β‐blockade would not exercise. Trout β‐blocked immediately after exercise showed a much higher incidence of mortality during the recovery period, but accompanying symptoms were similar to those previously documented in control trout dying after exercise. Specific effects of post‐exercise β‐blockade seen in both survivors and mortalities were a sustained elevation of arterial Pco 2 and an inhibition of blood glucose elevation. There were negligible effects on RBC pHi and volume regulation, blood metabolic acid and lactate dynamics, or plasma ion changes. The results provide little support for the hypothesis that β‐adrenergic actions of plasma catecholamines are intimately involved in post‐exercise recovery, but must be considered in the context of the ‘winter’ trout, where β‐responses may be diminished.