Dopamine: precursor or neurotransmitter in sympathetically innervated tissues?

Dopamine represents 1-5% of the total catecholamine pool in sympathetically innervated tissues. A substantial proportion of this dopamine is located in vesicles, and nerve activation results in liberation of dopamine as well as noradrenaline. In certain tissues, there is neurochemical and functional evidence for the existence in addition of separate populations of dopaminergic sympathetic nerves. Some of the unsolved questions relating to the neural release of dopamine are: Is intravesicular dopamine in noradrenergic nerves a stable storage pool? Do noradrenergic nerves release dopamine and noradrenaline by identical mechanisms? What physiological roles do the sympathetic dopaminergic nerves play? What are the diagnostic and therapeutic implications of neural dopamine release?