Dopamine-β-hydroxylase (DβH) activity assay
For the determination of DβH activity in plasma, venous blood samples (6
mL) were drawn into lithium heparin tubes, 30 minutes after breakfast on
day -1 and at pre-dose (within 10 minutes) on days 3, 6, 8, and 10.
The DβH activity assay relied on the conversion of tyramine to
octopamine by DβH; octopamine was then determined in plasma, in
accordance with the applicable principles of Good Laboratory Practices
(GLP), using a previously validated LC-MS/MS analytical method. DβH
activity was calculated as follows: