Dopaminergic instability in children with orthostatic dysregulation.

Effects of postural change on plasma catecholamine levels were examined in 53 children with orthostatic dysregulation (OD). Special interest was focused on plasma dopamine and dopamine-beta-hydroxylase (DBH) activity, since one patient showed a prominent rise in plasma dopamine from 822 pmol/L to 126 nmol/L in postural change. She had a wide fluctuation of plasma dopamine from 209 pmol/L to 305 nmol/L during 12 hours of observation period, but plasma norepinephrine and epinephrine remained within the normal range as well as urinary excretion of catecholamines. Of 52 children with OD, 11 had a marked increase in plasma dopamine, whereas 11 showed a reduction of it by postural change. Plasma DBH activity was significantly decreased in the former (81 +/- 14 nmol/h/ml), while it was elevated in the latter (320 +/- 48 nmol/h/ml, P less than 0.001 vs the former), although DBH activity in individuals was not affected by postural change. These results indicate the involvement of dopaminergic instability as a cause of OD in childhood.