The exercise-induced responses of arterial blood ammonia and plasma catecholamines were investigated in comparison with the lactate threshold (LT) during graded exercise. Prior to the experiment, six male subjects performed graded exercise test on a bicycle ergometer to determine LT. Each subject underwent an individually-set graded exercise test, which consisted of nine different workloads, including four low-intensity exercise below LT, one at LT, and four high-intensity exercise above LT. The mean rate of increase of exercise intensity was 18±1% (SE) of the workload at LT. Mean work load, heart rate, and arterial blood lactate concentration at LT were 100±4 watts,119± 3 beats/min, and 1.6±0.1mmol/l, respectively. Both arterial blood ammonia and plasma noradrenaline levels were increased as exercise intensity increased. The exercise thresholds were determined from inflection at which these parameters began to increase during graded exercise. The thresholds of blood ammonia and plasma noradrenaline were closely related to LT in all subjects. However, it was difficult to define the thresholds of plasma adrenaline and dopamine during graded exercise, because the levels of these factors in plasma were low. These result suggest that LT corresponds to the threshold where both adenosine monophosphate deamination in working muscles and sympathetic excitation begin to be activated during graded exercise.

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Lesch-Nyhan syndrome is caused by complete deficiency of hypoxanthine guanine phosphoribosyltransferase (HPRT). By the analysis of genomic DNA and mRNA using polymerase chain reaction (PCR) technique coupled with direct sequencing of the HPRT gene, five independent mutations in HPRT genes have been identified in Korean Lesch-Nyhan families. Two novel mutations (533-9T→A and 631delA) and three previously reported mutations (310insG, Q109X, and 289delGT) have been found in five independent families. In two previously reported mutations (Q109X, and 289delGT), we first detected secondary abnormal mRNAs with splicing error. Heterozygous carriers were detected in all the families, and prenatal diagnosis was carried out in two families.

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