EFFECTS OF ACUTE CARDIOSELECTIVE AND NONSELECTIVE BETA-ADRENERGIC-BLOCKADE ON PLASMA AMMONIA LEVELS IN EXERCISING DOGS

The aim of this study was to assess plasma ammonia levels during acute treadmill exercise in dogs after intravenous administration of a sing le dose of different cardioselective (atenolol) and non-selective (sot alol and propranolol) beta-adrenergic blocking drugs. The experiments were performed on 6 male mongrel dogs (20-25 kg) trained to run on a m otor driven treadmill. After administration of saline or atenolol, the re was no significant increase in plasma ammonia during exercise; prop ranolol and sotalol however, both non-selective beta-blockers, produce d a significant increase in plasma ammonia. Plasma levels of alanine a nd glutamine were not altered during exercise compared with resting va lues, and were not modified by the administration of beta-blockers. It is not clear whether the different effects on exercise induced hypera mmonemia are due to different effects on muscle ammonia formation or o n the ammonia clearance by the liver.