Secretins

Secretin is a hormone that regulates the water balance of the whole body. It affects the environment of the duodenum by regulating the secretions of the stomach, pancreas, and liver. It is a peptide hormone produced by the S cells of the duodenum located in the intestinal gland. The amino acid sequence of secretin is H-His-Ser-Asp-Gly-Thr-Phe-Thr-Ser-Glu-Leu-Ser-Arg-Leu-Arg-Asp-Ser-Ala-Arg-Leu-Gln-Arg-Leu-Leu-Gln-Gly-Leu-Val-NH2. Secretory peptides are encoded by the SCT gene in humans. Secretin was originally synthesized into a 120-amino acid precursor protein known as prosecretin. The precursor contains an N-terminal signal peptide, a spacer, secretin itself (28-54 residues), and a 72-amino acid C-terminal peptide. The mature secretory peptide is a linear peptide hormone composed of 27 amino acids with a molecular weight of 3055. A helix is formed between amino acid positions 5 and 13. The amino acid sequence of glucagon was similar to that of glucagon, vasoactive intestinal peptide (VIP) and gastric inhibitory peptide (GIP).

Mode of Action

Secretin regulates pH in the duodenum by inhibiting gastric acid secretion by gastric parietal cells and stimulating pancreatic ductal cells to produce bicarbonate. It also stimulates the liver to produce bile, which emulsifies dietary fat in the duodenum so that pancreatic lipase can act on it. At the same time, under the action of secretin, another major hormone secreted by the duodenum, cholecystokinin, stimulates gallbladder contraction, releasing stored bile for the same reason.

Function

The effect of secretin is to stimulate the pancreas to secrete a large amount of pancreatic juice rich in bicarbonate, and to produce the maximum stimulating dose of trypsin in humans, dogs and pigs, which is a clinical unit of intravenous injection or intravenous infusion per kilogram of body weight per hour, which is equivalent to 200 to 250 nanogrammes. It has a weak strengthening effect on trypsin secretion, but if given together with trypsin, it can significantly increase trypsin secretion and inhibit gastric acid secretion and gastrointestinal activity in human, dog and rat.

References

1. Mynatt, R. L., & Ravussin, E. (2018). Secretin: An Old Hormone with a Burning Secret. Cell, 175(6), 1459-1460.
2. SINGH, K., Leprince, J., Lefranc, B., Vaudry, D., & Chow, B. K. C. (2018). Discovering small compound modulators for Secretin receptor. Cambridge Healthtech Institute's 13th Annual Drug Discovery Chemistry. April 2-6, 2018 in San Diego, CA USA.