Mechanisms of storage and exocytosis in neuroendocrine tumors.

Excitatory and inhibitory neurotransmitters and biogenic amines are important signaling molecules stored by and released from endocrine cells. They are either synthesized or taken up by endocrine cells and subsequently stored in secretory vesicles. Analysis of these storage mechanisms and of the receptors of these paracrine signaling molecules revealed important cross-talk within endocrine glands which add to storage and release of peptide hormones. Components of the exocytosis apparatus are shared by the release of transmitters and hormones. They, as other classical markers, can serve as broad spectrum markers for neuroendocrine tumors. Novel specific markers arise from studies of the synthesis, uptake, and targets of transmitters identified as an additional paracrine signaling system in endocrine systems.