Human Biochemistry, Volume 2 - Murray R. 1993

Biochemistry of Intra- and Intercellular Communication
Gastrointestinal Hormones
Other Gastrointestinal Peptides

Several other Peptides have been isolated from gastrointestinal Tissues that apparently participate in the Regulation of Digestion (likely via paracrine or neurocrine mechanisms, as they have not been detected in significant amounts in the Blood). It should be emphasized that a definitive physiological role has not yet been established for any of these molecules.

Substance P was the first peptide discovered in both the gut and the Brain. The activity of this 11-peptide, which manifests as The stimulation of intestinal smooth Muscle contractions, requires the 5 C-terminal Amino Acids. Bombesin was originally found in frog Skin, but a similar peptide, commonly referred to as gastrin-releasing peptide (GRP), has been isolated from intestinal endocrine Cells, enteric Neurons, and the brain. The amino acids at positions 5–14 of bombesin are identical to positions 18–27 of gastrin-releasing peptide, with the exception of a single residue. Bombesin stimulates gastric and pancreatic secretion and enhances Gallbladder and intestinal motility. This peptide may also exert a growth-promoting autocrine effect on small Cell lung carcinoma. Motilin is a 22-peptide produced in the intestinal mucosa. It increases gastric mucosal acid and Pepsin secretion and, in addition, stimulates intestinal smooth Muscle contraction. Somatostatin is produced by gastric D cells and inhibits (via a paracrine action) the secretion of gastrin, secretin, cholecystokinin, motilin, and gastric inhibitory polypeptide. Glucagon is produced in the A Cells of the gastric mucosa. It is quite likely involved in mediating the metabolic effects of pancreatic glucagon. Other peptides with glucagon-like immunoreactivity (GLI) have been isolated from L cells of the ileum and colon. The major component of GLI is a large 100-amino-acid peptide called glicentin, which precisely incorporates the Amino Acid Sequence of pancreatic glucagon. Glicentin can mimic the actions of glucagon. Neurotensin (a 13-peptide), met- and leu-enkephalins, as well as serotonin, have been found in intestinal cells and may exhibit activity within its tissues. Approximately 40 peptides have been identified in neural tissues, and it is highly likely that an even greater number of Gastrointestinal Peptides await discovery.

Class="center">References

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