Neurotensin (NT), a biologically active tridecapeptide isolated from the hypothalamus, is expressed in both the central nervous system and in various peripheral organs, including intestinal mucosa, adrenal gland and pituitary. The NT gene encodes a 170-amino acid precursor protein containing both the tridecapeptide NT and a closely related hexapeptide - neuromedin N (NN). The four amino acids at the C-terminus of NT and NN are identical, and the 6-amino acids (8-13) on the C-terminus of NT are essential for biological activity. In neurons, NT is stored in dense core vesicles and released in a Ca2+-dependent manner. Several peptidases such as endopeptidase and angiotensin-converting metalloendopeptidase cleave NT, terminating its transmission. NT acts as a neurotransmitter that stimulates the electrical activity of neurons. In addition to functioning as a neurotransmitter or neuromodulator. It plays an important role in the central nervous system affecting gastrointestinal function. It inhibits gastric acid secretion and maintains gastric mucosal blood flow during cold water restraint in rats. It also regulates the release of various pancreatic hormones, adrenal and pituitary glands, as well as some cellular functions of the peripheral immune system including the cutaneous inflammatory process. NT agonists or antagonists have been suggested to be of potential use for the treatment of pain, eating behavior, psychotic troubles, drug abuse, and stress. NT responses are known to be mediated through at least three receptors identified to date- NTR1, NTR2 and NTR3. Overexpression of NT receptors in various tumors suggests that NT-related ligands could represent valuable tools for tumor targeting.
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