KINETICS OF PLASMA 3,4-DIHYDROXYPHENYLALANINE (DOPA) DURING PHYSICAL EXERCISE - A COMPARATIVE-STUDY WITH THAT OF PLASMA NORADRENALINE

To assess the usefulness of 3,4-dihydroxyphenylalanine (DOPA) in blood plasma as an indicator of sympathetic nervous activity, the relationship between plasma DOPA and indicators of circulatory function being closely related to the sympathetic tone was investigated in young male subjects with loading an ergometer exercise for 5 minutes. Two experimental protocols were administered; 1) one to detect the relationship between the plasma DOPA level and the sympathetic tone expressed in circulatory function indicators and 2) the other to confirm the relationship between the plasma noradrenaline (NA) level and the sympathetic tone. The results were analyzed with analysis of variance (ANOVA) with regard to the two factors affecting data variance. namely time and the person (individual variation) factors. The time factor was considered relative to the exercise load. The data variances in circulatory indicators and plasma NA were affected by both of the factors, but that in plasma DOPA was affected only by the enormous variation in the basal DOPA levels among individuals. Circulatory indicators such as heart rate, systolic and diastolic blood pressures and plasma NA changes against time showed a concomitant trend and those levels increased during exercise. Plasma DOPA levels increased a little only 2 minutes after completion of the exercise. An index derived from a calculation using the ratios of systolic blood pressure and heart rate to the respective basal level at 0 time seemed to express sympathetic tone, and the latter increased proportionally to the ratio of plasma NA to its basal value when the latter was within 4.6 times above the basal value. The trend of sympathetic tone became inversely proportional to the NA ratio, if the latter was more than 4.6 times the basal value. There was no special relationship suggesting functional expression between plasma DOPA and the index of sympathetic tone.