Pancreatic Polypeptides
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Introduction
Pancreatic polypeptide (PP) is a polypeptide secreted by PP cells in the endocrine pancreas predominantly in the head of the pancreas. It is a straight-chain 36-amino acid polypeptide derived primarily from the pancreas and localized in the islets and scattered among the acinar cells of the exocrine pancreas. It has a molecular weight about 4200 Da. It belongs to the neuropeptide Y (NPY) peptide family and contains several tyrosine residues and is C-terminal amidation. It has a tertiary structure, the so-called PP-fold, it is U-shaped with an extended polyproline helix and α helix connected by β turn. PP can self-regulate pancreatic secretion (endocrine and exocrine), and also affect hepatic glycogen level and gastrointestinal secretion. Thus PP may have an important physiological role in the regulation of pancreatic function.
Mechanism of action
The secretion of PP is affected by several different stimuli, and vagal cholinergic stimulation (vagal cholinergic stimulation), which is one of the key mechanisms to regulate the release of peptides. Cholinergic mechanisms have long been known to regulate the secretion of other pancreatic hormones. Studies have shown that cholinergic vagal activity is the most potent stimulation of peptide secretion. When cholinergic receptors muscarinic receptors are blocked or vagotomy almost all other stimuli lose their effect in vivo. In addition, other stimuli of extracorporeal agents lose their effect, while cholinergic stimuli remain effective. Even under basic conditions, the secretion of PP is in cholinergic state. Therefore, the secretion of PP is a model to study the control of vagus nerve on the endocrine system at the level of Vago-reflex at the level of afferent, central and efferent. Therefore, the secretion of PP is unique, cholinergic, vagal stimulation is not only the most powerful stimulation mechanism, but also the key to other mechanisms. PP secretion can be used as a sensitive indicator of autonomic nervous dysfunction in diabetic patients.
Application of Pancreatic Polypeptide
Pancreatic polypeptide, peptide secreted by the F (or PP) cells of the islets of Langerhans in the pancreas, which contains 36 amino acids. Its secretion is stimulated by eating, exercising, and fasting. Pancreatic polypeptide is a central feature in a variety of pathological situations. A partial list includes such as insulinomas, gastrinomas, gastric cancer, chronic pancreatitis, pancreatic cancer, cirrhosis, diabetes. PP has become a promising target for the treatment of some diabetes.
References
- Schwartz, T. W. (1983). Pancreatic polypeptide: a unique model for vagal control of endocrine systems. Journal of the Autonomic Nervous System, 9 (1), 99-111.
- Jung, G., Louie, D. S., Owyang, C. (1987). Pancreatic polypeptide inhibits pancreatic enzyme secretion via a cholinergic pathway. Am J Physio, 253(1), 706-710.
- Modlin, I. M., Albert, D., Crochelt, R., Sank, A., Jaffe, B. M. (1981). Evidence for an intestinal mechanism of pancreatic polypeptide release. Digestive Diseases & Sciences, 26(7), 587-590.
