Neurotensins and Related Peptides
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Introduction
Neurotensin (NT) is one of many bioactive peptides and its family mainly includes two biologically active peptides, namely NT with 13 amino acids and neuromedin N (NN) with 6 amino acids. The NT gene encodes a 170 amino acid precursor protein that contains both the tridecapeptide NT and a closely related hexapeptide-neuromedin N. Both peptides are derived from the same precursor with similar pharmacological properties and tissue distribution.
Some NT-related peptides (NRPs) exist primarily in precursor forms which can be processed artificially by the enzyme pepsin. NRP can be produced by releasing acidic cathepsin from leukocytes during an ischemic or inflammatory state to modulate tissue perfusion. However, two immunoreactive neurotensin-related peptides produced by the action of endogenous protease(s) on protein substrates during acid extraction of avian tissues. Each peptide showed partial homology to the C-terminal.
Mechanism of action
The mechanisms have been thoroughly investigated about extracellular NT and NN are inactivated in the circulation and in tissues. It has been shown that both NT and NN are released on depolarization of brain tissues. Meanwhile, after food ingestion, intestinal NT and large NN are secreted in the circulation. There is increasing pharmacological evidence indicates both NT and NN have similar affinities to the three NT receptor subtypes and that NN exhibits similar biological characteristics to NT. In addition, large NN has been shown to have NT-like biological activity in intestinal preparations. However, NN is rapidly inactivated by aminopeptidases while NT is slightly more slowly inactivated by metalloendopeptidases which cleave peptides in their C-terminal domains.
Application of neurotensins and related peptides
Some studies show that NT and its variants have important roles in a number of basic physiological processes, such as digestion, temperature regulation, blood flow, and nociception. In addition, NT plays an important role in the central nervous system that affects gastrointestinal function. What’s more, it inhibits gastric acid secretion and maintains gastric mucosal blood flow during cold water inhibition in rats. More importantly, it can regulate the release of various pancreatic hormones, adrenal and pituitary glands, as well as some cellular functions of the peripheral immune system, including the inflammatory process of the skin.
References
- Carraway, R. E., Cochrane, D. E., & Ruane, S. E. (1987). Isolation, structures, and biologic activity of neurotensin-related peptides generated in extracts of avian tissue. Journal of Biological Chemistry, 262(33), 15886-15889.
- Vanneste, Y., Thome, A. N., Vandersmissen, E., Charlet, C., Franchimont, D., Martens, H., ... & Geenen, V. (1997). Identification of neurotensin-related peptides in human thymic epithelial cell membranes and relationship with major histocompatibility complex class I molecules. Journal of neuroimmunology, 76(1-2), 161-166.
