An alpha-adrenergic sympathomimetic amine, biosynthesized from Tyramine in the CNS and Platelets and also in Invertebrate Nervous Systems. It is used to treat Hypotension and as a cardiotonic. The natural D(-) form is more potent than the L(+) form in producing cardiovascular adrenergic responses. It is also a Neurotransmitter in some Invertebrates.