Carbohydrate availability affects ammonemia during exercise after beta 2-adrenergic blockade.
OBJECTIVE
Beta-adrenergic blockade increases blood ammonia concentration during exercise. The purpose of this study was to assess the role of decreased carbohydrate availability in this process.


METHODS
Wistar rats (N = 47) were injected intravenously with a selective beta 2-adrenoceptor blocker (ICI 118,551), placebo, or beta 2-blocker + glucose 1 h before a treadmill exercise test. Blood samples were taken to measure the concentration of ammonia, glucose, lactic acid, free fatty acids (FFA), glycerol, branched-chain amino acids (BCAA), and muscle samples for determination of glycogen content.


RESULTS
Beta 2-adrenergic blockade shortened running time to exhaustion (23 +/- 4.3 min compared to 44 +/- 5.2 min with placebo), increased blood ammonia levels (146.7 +/- 16.21 micromol x L(-1) compared to 47.5 +/- 0.92 micromol x L(-1) with placebo) and prevented exercise-induced glycogen breakdown in soleus and gastrocnemius muscles. Pre-exercise supplementation of glucose during beta 2-blockade restored exercise-induced glycogen breakdown and reduced blood ammonia concentration during exercise (66.5 +/- 5.65 mmol x L(-1)) but did not improve exercise capacity (26 +/- 3.2 min) when compared with beta2-blockade alone.


CONCLUSIONS
The results suggest that the enhanced rise in blood ammonia concentration during exercise after beta-blockade is caused by impaired carbohydrate availability.
Matthys
D
D
Department of Pediatric Cardiology, Institute of Kinesiology and Sport Sciences, University of Ghent, Belgium. dirk.matthys@rug.ac.be
Derave
W
W
Calders
P
P
Pannier
J L
JL
D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage*; D000597:Amino Acids, Branched-Chain / Q000097:blood; D000641:Ammonia / Q000097:blood*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002241:Carbohydrates / Q000097:blood*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005990:Glycerol / Q000097:blood; D007275:Injections, Intravenous; D007773:Lactates / Q000097:blood; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D011412:Propanolamines / Q000008:administration & dosage; D051381:Rats; D017208:Rats, Wistar; D012420:Running / Q000502:physiology*
D000319:Adrenergic beta-Antagonists; D000597:Amino Acids, Branched-Chain; D001786:Blood Glucose; D002241:Carbohydrates; D005230:Fatty Acids, Nonesterified; D007773:Lactates; D011412:Propanolamines; C026777:ICI 118551; D000641:Ammonia; D005990:Glycerol