[Effect of lactulose on ammonia metabolism during exercise]

In seven athletes, the effects of lactulose on ammonia metabolism during dynamic exercise were studied with a cycle ergometer. Each subject performed a graded incremental test with increases in work rate of 300 kpm/3 min until exhaustion set in, on two separate days, one without lactulose and one with 20 mg/day lactulose for 3 days. Without lactulose, maximal heart rate and peak oxygen uptake (VO2) were 193 beats/min and 4280 ml/min, respectively. LA was unchanged early in exercise, but elevated rapidly at work rates of 900 kpm (54% peak VO2) and thereafter. AMM increased even at rates as low as 600 kpm (40% peak VO2) and continued to rise attaining peak value at the termination of exercise. After exercise, AMM decreased rapidly. On the other hand, LA was still significantly above the basal level after 30 min of recovery. After lactulose, heart rate, duration of exercise or LA was not significantly different from the value without lactulose at the same work rate, however, AMM at low work rate was lower and VO2 at 1500 kpm was higher. Lactulose had small but significant effects on some parameters of graded exercise.