Ammonia metabolism during exercise in man

Abstract

Physical exercise is accompanied by increased plasma levels of ammonia but it is not known whether this rise primarily reflects accelerated formation in muscle or decreased removal by the liver. Consequently, leg and splanchnic exchange of ammonia was examined, using the catheter technique, in 11 healthy subjects at rest, during three consecutive 15 min periods of bicycle exercise at gradually increasing work loads (35%, 55% and 80% of maximum oxygen uptake) and for 60 min during post-exercise recovery. The basal arterial ammonia level was 22 +/- 2 mumol/l, the concentration rose curvilinearly in response to increasing work loads (peak value 84 +/- 12 mumol/l), and fell rapidly after exercise, reaching basal levels after 30-60 min. A linear regression was found for ammonia levels in relation to lactate concentrations at rest and during exercise (r = 0.85, P less than 0.001). A significant relationship was also observed between arterial ammonia and alanine levels (r = 0.75, P less than 0.001). Leg tissues showed a net uptake of ammonia in the basal state (2.4 +/- 0.5 mumol/min). During exercise this changed to a net production, which increased curvilinearly with rising work intensity (peak value 46 +/- 15 mumol/min) but reverted to a net ammonia uptake at 30-60 min after exercise. Splanchnic ammonia uptake (basal 12 +/- 2 mumol/min) did not change in response to exercise but increased transiently during the early post-exercise period. From the above observations we conclude that the hyperammonaemia of exercise comes primarily from muscle release, while the splanchnic removal of ammonia is essentially unaltered. Part of the ammonia formed in contracting muscle is most likely used in the synthesis of amino acids, mainly glutamine and probably alanine.

The Contribution of Various Organs to Ammonia Formation: A Review of Factors Determining the Arterial Ammonia Concentration

“…During exercise, muscle ammonia is mainly derived from increased activity of the purine nucleotide cycle." Ammonia release from skeletal muscle during exercise has also been described by Eriksson et al 34 Katz et .al. 35 calculated a release rate of about 130 mmol124 h at maximal workload.…”

Exercise-induced changes in amino acid levels in skeletal muscle and plasma

“…Furthermore, isometric contraction exercise with two-thirds maximum voluntary contraction to fatigue decreased glutamate levels, but increased alanine and pyruvate levels in muscles 25) . Eriksson et al 26) conducted a detailed investigation of the release and uptake of free amino acids in muscles by monitoring arteriovenous oxygen differences during cycle ergometer exercise with gradually increasing workloads (30%, 55%, and 80% of V ・ O2max: 15 min at each workload level). They found that the amount of alanine released from exercising muscles increased significantly by 2.7-fold and 8.9-fold during exercise with a load of 55% and 80% of V ・ O2max, respectively, compared with pre-exercise levels.…”

Physical activity, protein metabolism and protein requirements

“…300% increase at 55% Vo,,, and 900% at 80% VO,,~, Eriksson et al 1985). The increase in glutamine release is less and in any case is partly at the expense of intramuscular glutamate (Eriksson et al 1985;Katz et al 1986;Henriksson, 1991). Trained athletes tend to oxidize more fat and less carbohydrate than the general population; therefore, because amino acid oxidation roughly matches glycogen utilization, alanine production (an indicator of amino acid oxidation) by trained athletes is less (see Rennie et al 1994).…”