The influence of methylphenidate on the sympathoadrenal reactivity in children diagnosed as hyperactive

In order to investigate whether catecholamines play a role in the hyperkinetic child syndrome, we determined noradrenaline and adrenaline plasma levels before and after treatment with methylphenidate. The children were separated into drug responders and non-responders according to the efficacy of methylphenidate on behavioral symptoms. 21 children, 6-13 years of age, participated in this double-blind placebo controlled cross-over study. Conners' questionnaire was used to estimate the extent of the hyperactivity and to assess the drug response. Blood samples were drawn under resting and exercise conditions and plasma catecholamine concentrations determined as an indication of the amine release rate and the reactivity of the sympathoadrenal system. The results may be summarized: The postexercise noradrenaline levels of untreated hyperkinetic children were slightly, but not significantly higher than those of an age-matched control group. After 3-4 weeks of stimulant medication the noradrenaline release induced by physical exercise was significantly lower than after placebo. 12 out of 21 children showed an alleviation of their symptoms during methyl- phenidate therapy and thus could be assumed as drug-responders. When children were separated into drug-responders and non-responders according to the degree of the clinical improvement, both groups showed the same catecholamine release in response to exercise. Methylphenidate reduced the noradrenaline release in 9 out of 11 children in the responder group and in 7 out of 9 children in the non-responder group. In conclusion, catecholamines may be involved in the hyperkinetic child syndrome, but because of the heterogenity of this syndrome the depression of the plasma catecholamines as observed under methylphenidate could not differentiate between drug-responders and non-responders.