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 beta-adrenoceptors 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 mumol/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 mumol/l; p < 0.05), and diminished by the administration of glucose (42 +/- 7.7 vs 78 +/- 7.9 mumol/l; p < 0.05). These results suggest that increased metabolisation of BCAA is involved in the ammonia formation after beta-adrenergic blockade.