Influence of ambient temperature on plasma ammonia and lactate accumulation during prolonged submaximal and self-paced running

This study examined the effects of heat stress on the accumulation of plasm a ammonia, lactate, and urate during prolonged running. Nine highly trained endurance runners completed two running trials in a counterbalanced fashio n in cool (15 degreesC) and in hot (35 degreesC) humid (60% relative humidi ty) conditions. Subjects ran on a motorised treadmill at 70% of peak treadm ill running speed for 30 min (submaximal) followed by a self-paced 8-km per formance run. Blood was drawn at pre-exercise, end-submaximal and end-perfo rmance run and analysed for plasma ammonia, lactate, and urate. Four subjec ts failed to complete the performance run in the heat and the performance t imes for the rest of the subjects was increased from 27.3 (0.6) min in cool conditions to 31.3 (1.2) min in hot conditions (P < 0.05). The end-perform ance rectal temperature was 38.6 (0.1) and 39.2 (0.1)degreesC (P < 0.05) in cool and hot conditions, respectively. Differences in plasma lactate at th e end of submaximal running were not significant. However, at the end of pe rformance runs lactate was 6.0 (0.9) mmol.l(-1) in cool and 3.1 (0.5) mmol. l(-1) in hot conditions, values that were significantly different (P < 0.05 ). Plasma ammonia increased from pre-exercise to congruent to 59 mu mol.l(- 1) at the end-submaximal runs for both coditions and further at the end of performance runs to 108.5 (11) mu mol.l(-1) (P < 0.05) in hot but not in co ol conditions. Plasma urate increased from pre-exercise to 311.2 (25.9) mu mol.l(-1) at end-submaximal runs and to congruent to 320.4 mu mol.l(-1) at end-performance runs in hot and cool environments. The findings that plasma urate accumulation was similar at the completion of running in both condit ions, while ammonia was significantly augmented in hot conditions compared with cool, suggest that ammonia accumulation during heat stress exercise mi ght be derived from sources other than purine catabolism.