Observations on the Effect of Exercise on Blood Ammonia Concentration in Man †

In 1925 Luck, Thacker and Marrack reported elevated blood ammonia levels in epileptic patients after grand mal seizures.1' Although they suspected that muscular exercise might be responsible for this rise, they apparently excluded this possibility by their inability to produce increased venous ammonia levels by vigorous muscular exercise. Several years later Parnas and his co-workers noted that the blood ammonia concentration was elevated in the veins which drained the exercising forearms of normal subjects.' These investigators demonstrated that ammonia liberated by the muscle during fatiguing exercise was responsible for this rise. These observations were confirmed by Kalk and Bonis.'7 Recently, Schwartz, Lawrence, and Roberts re-investigated some aspects of this problem.' They induced convulsions in dogs and observed an increase in the arterial ammonia concentration which could be prevented by suppressing the motor aspects of the convulsions with AnectineI4. In addition, they were able to produce increased systemic blood ammonia levels in normal men by vigorous generalized exercise. The recognition by Bessman and his co-workers of the importance of the peripheral tissues in ammonia metabolism has given fresh significance to these earlier observations. These investigators showed that as the arterial ammonia concentration rises in patients with hepatic coma, the peripheral tissues extract correspondingly large amounts of ammonia."' These findings which were based on simultaneous arterial and venous ammonia determinations have been confirmed"' 3034 and extended to show that in the terminal phases the peripheral tissues may sometimes liberate ammonia into the systemic circulation.0" Similar observations have been made following the administration of ammonium salts to normal subjects and animals."' "' The significance of the uptake of ammonia by the peripheral tissues, presumably muscle, is not clear. It has been suggested that this extraction of am-