Effects of Acute Non-Selective Beta-Adrenergic Blockade on Plasma Ammonia Levels in Exercising Dogs

The purpose of the present study was to document exercise induced hyperammoniemia after blockade of the β-adrenoreceptors and to investigate the effect of administration of branched-chain amino acids (BCAA) and glucose in these conditions. Seven dogs, chronically instrumented with a catheter in the deep jugular vein and a Doppler probe around the carotid artery were trained to perform a ten-minute treadmill exercise test. Administration of propranolol i.v. prior to exercise increases plasma ammonia at peak exercise compared with placebo (78 ± 7.9 vs 25 ± 5.1 μmol/l; p < 0.05). This effect of propranolol on plasma ammonia during exercise is enhanced by the administration of BCAA (108 ± 15 vs 78 ± 7.9 μmol/l; p < 0.05), and diminished by the administration of glucose (42 ± 7.7 vs 78 ± 7.9 μmol/l; p < 0.05). These results suggest that increased metabolisation of BCAA is involved in the ammonia formation after β-adrenergic blockade.

Key words

Ammonia - exercise - branched-chain amino acids - beta adrenergic blockade