Insulin-like peptide 5: a new key player in IBS with diarrhoea and bile acid malabsorption?

When considering the endocrine system, the GI tract is commonly overlooked, while it is in fact the largest endocrine organ in the human body. The GI tract lining comprises specialised enteroendocrine cells (EECs) which together produce over 20 bioactive peptide hormones.1 These are secreted in a spatial-temporal manner, generally in response to digestive cues. The clinical success of gut-peptide based pharmacotherapy, mostly based on the incretin glucagon-like peptide-1 (GLP-1), has directed the recognition of the power of gut-derived hormones and sparked scientific and public interest in this field. Even prior to these recent developments, postoperative changes in gut peptide levels after bariatric surgery provided us with compelling evidence of the pivotal role played by gut hormones in appetite regulation and glucose homeostasis. However, the physiological action of gut peptides extends far beyond mere appetite regulation, encompassing the control of GI motility, secretion and visceral sensitivity. Given the widespread distribution of gut peptide receptors throughout the body, it is arguable that their systemic effects are far-reaching and yet to be fully understood.