Relationship between ammonia, heart rate, and exertion in McArdle's disease.

We studied plasma ammonia and exercise tolerance in six patients with McArdle's disease (myophosphorylase deficiency, type V glycogenosis) during incremental cycle ergometry. Tests were performed either in the postabsorptive state or after supplementation with branched-chain amino and 2-oxoacids and glucose. Glucose and branched-chain 2-oxoacid combined increased total work performed from control 49 +/- 22 to 80 +/- 36 kJ (P less than 0.05). Glucose alone also improved total work performed from 49 +/- 22 to 64 +/- 33 kJ (P less than 0.05). Branched-chain 2-oxoacids alone had a variable effect, and branched-chain amino acids were of no benefit. Correlations between plasma ammonia and heart rate for individual patients were r = 0.99, P less than 0.01; r = 0.95, P less than 0.01; r = 0.84, P less than 0.01; r = 0.76, P less than 0.01; r = 0.73, P less than 0.01; and r = 0.63, P less than 0.05 and between ammonia and perceived exertion for all patients combined was r = 0.70, P less than 0.0001. In two patients, correlation of ammonia with heart rate at a power output of 60 W was r = 0.91, P less than 0.001 and at 40 W was r = 0.77, P less than 0.001. We conclude that ammonia is either a mediator or a marker of the metabolic events leading to fatigue.