Hormones of the Gut

Over two dozen hormones have been identified in various parts of the gastrointestinal system. We shall look at 8 of them here: The endocrine cells of the small intestine also secrete which are described on separate pages.

Gastrin

Somatostatin

This mixture of peptides is secreted by cells in the gastric glands of the stomach and acts on

Taken together, all of these actions lead to a reduction in the rate at which nutrients are absorbed from the contents of the intestine.

Somatostatin is also secreted by the hypothalamus and the pancreas.

Secretin

Cholecystokinin (CCK)

Fibroblast Growth Factor 19 (FGF19)

Incretins

The release of insulin from the pancreas is much greater when glucose is ingested with food rather than injected intravenously.

The reason: the arrival of food in the duodenum stimulates the release of polypeptides called incretins. The two most important are: Their effects:

All the actions prevent a sharp rise in blood glucose when consuming a sugar-rich meal.

Exenatide (Byetta®) and liraglutide (Victoza®) are synthetic peptides that mimic the action of GLP-1 but the effects are longer-lasting. They are being used to treat patients with type 2 diabetes.

Ghrelin

Ghrelin is a lipopeptide consisting of 28 amino acids with a covalently attached 8-carbon fatty acid.

Neuropeptide Y (NPY)

Neuropeptide Y contains 36 amino acids. It is a potent feeding stimulant and causes increased storage of ingested food as fat.

Velneperit is a drug that blocks the action of neuropeptide Y on its receptors. It is in clinical trials for the treatment of obesity.

Neuropeptide Y is also secreted by neurons in the hypothalamus where it
  • blocks the transmission of pain signals to the brain and
  • induces a calming effect in laboratory animals exposed to stressful situations.

PYY3-36

Peptide YY3-36 contains 34 amino acids, many of them in the same positions as those in neuropeptide Y.

But the action of PYY3-36 is just the reverse of that of NPY, being a potent feeding inhibitor.

It is released by cells in the intestine after meals. The amount secreted increases with the number of calories ingested and especially when these are derived from proteins rather than carbohydrates or fats. (This may explain the efficacy of the protein-rich, carbohydrate-poor Atkins diet.)

PYY3-36 acts on The appetite suppression mediated by PYY3-36 works more slowly than that of cholecystokinin and more rapidly than that of leptin. In a recent human study, volunteers given PYY3-36 were less hungry and ate less food over the next 12 hours than those who received saline. Neither group knew what they were getting, but one of the side-effects of injected PYY3-36 is a feeling of nausea and a bad taste to food which might account for these results!

Link to a table listing these, and other, hormones that either stimulate or suppress appetite.

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2 December 2013