[Gastrointestinal hormones--function and clinical significance. 1: The classical enterohormones gastrin, cholecystokinin and secretin].

Gastrointestinal endocrinology is undergoing a variety of different changes. Thus, many of the known hormones are seen no longer to fit the definition of endocrinology--rather, their regulation mechanism may be of a paracrine, neurocrine, neuroendocrine or autocrine nature, or the peptide may be a neurotransmitter. A better term than hormone would thus be regulatory peptide. A knowledge of the physiological mode of regulation of a peptide impacts not only on our understanding of pathophysiological processes, but also on the therapeutic use of peptides. In this Part, the classical gut hormones gastrin, secretin and cholecystokinin are described with the above aspects in mind. The well-known hormones have also been shown to have previously unsuspected biological actions, whose biological significance is, as yet, unknown. For example, cholecystokinin is now being considered as a regulator of glucose homeostasis, satiety and pancreatic growth.