Expecting to Eat: Glucagon-Like Peptide-1 and the Anticipation of Meals

Abstract

We have known for more than a century that the sight, smell, and taste of food can provoke a number of physiological responses referred to as cephalic because they are initiated by the central nervous system (CNS) and not by direct gastrointestinal contact with food (1,2,3). These responses can be elicited by previously arbitrary cues that have become associated with the presentation of food, including sounds or time of day (4). In this sense, cephalic phase responses are a physiological manifestation of an animal’s prediction that food is on the way. Cephalic insulin and pancreatic polypeptide responses have been among the most well studied, and such food-anticipatory secretions are observed in multiple species, including humans (3,5,6). A variety of evidence suggests that the function of these cephalic responses is to better prepare the organism to handle the influx of nutrients about to occur (7). Several studies support the idea that these cephalic responses are indeed required for an animal to be fully capable of ingesting large meals; in their absence, intake is reduced (8,9). In this issue, Vahl et al. (10) reported that we can now add glucagon-like peptide (GLP)-1 to the list. Using rats maintained on a highly restrictive meal-feeding schedule, which tends to exaggerate meal-anticipatory responses, they identified a robust premeal rise in plasma GLP-1 levels. Moreover, they showed that intake during that scheduled meal was reduced by blockade of GLP-1 receptors during the premeal period.