Neurotensin is a secreted tridecapeptide, which is widely distributed throughout the central nervous system, and may function as a neurotransmitter or a neuromodulator. It may be involved in dopamine-associated pathophysiological events, in the maintenance of gut structure and function, and in the regulation of fat metabolism. Tissue-specific processing may lead to the formation in some tissues of larger forms of neuromedin N and neurotensin. The large forms may represent more stable peptides that are also biologically active.