The gut hormone response to food

The functioning of the gastrointestinal tract is controlled ( I ) by a complex system of extrinsic and intrinsic nerves that secrete both peptide and non-peptide neurotransmitters, ( 2 ) by paracrine cells that secrete their products into the immediate surroundings, and (3) by mucosal endocrine cells that secrete peptides into the circulation. Together, these components form the 'diffuse neuroendocrine system' (Polak & Bloom, 1980) which exerts a finely-modulated control over every element of gut function. The many peptides secreted by this system are often loosely called 'gut hormones', but only for one of these, gastrin, is there sufficient evidence that it acts as a hormone under physiological conditions. Neuropeptides such as vasoactive intestinal polypeptide may overspill into the circulation, as may peptides such as somatostatin which fulfils both a paracrine and a neurocrine role. This does not mean that such peptides function as true hormones. This account will be ccnfined to the peptide products of the mucosal endocrine cells that release them into the blood in response to luminal stimuli. Table It will be seen that many of them occur in multiple molecular forms, both with respect to chain-length and, in the case of the gastrins, with respect to sulphation of the tytosyl residue at the active site of the molecule.