Hyperammonaemia in relation to high-intensity exercise duration in man.

Adenine nucleotide (AN) degradation has been shown to occur during intense exercise in man and in the horse, at or close to the point of fatigue. The aim of the study was to compare plasma ammonia concentration ([NH3]) as a result of intense exercise with plasma [lactate]. Plasma glutamine concentration ([Gln]) was also measured pre- and post-exercise. On separate occasions, nine healthy subjects (two females) exercised on a motorised treadmill for periods of between 30 s and 210 s, at 5.6 m.s-1 (0% incline). On one occasion, running at the same speed, two subjects ran at +4% incline whilst one other subject ran at +7% incline. Blood samples were taken and plasma was analysed for [lactate], [NH3] and [Gln]. Subjects showed varying degrees of AN degradation as indicated by plasma [NH3]. A comparison of plasma [NH3] with that of plasma [lactate] indicated a marked increase in AN degradation, corresponding to a [lactate] of around 14 mmol.l-1 in plasma. The data further support the hypothesis that there is a critical intramuscular pH below which there is a stimulus to AN degradation during intense exercise, possibly as a result of a substantial reduction in the kinetics of adenosine diphosphate (ADP) rephosphorylation provided by phosphocreatine, resulting in an increase in [ADP].