The role played by L-dopa decarboxylase in the biosynthesis of catecholamines depends on the organ in which the primary product of its action, i.e., dopamine, is formed.
In the suprarenal medulla the biosynthesis proceeds via noradrenaline to the methylated end-product, adrenaline. Dopamine is the precursor of the hormones.
In nervous tissue, the biosynthesis stops at the noradrenaline level. Here dopamine is the precursor of the transmitter, and besides this probably an effector substance of its own.
In lungs, intestine and liver dopamine itself is the end-product of the biosynthesis. Here it may act as a local hormone.