By tradition, experimental studies of gastrointestinal physiology and pathophysiology in humans and in intact animals have been conducted after an overnight fast, but the presence of food itself has considerable effects on the intestinal function. We have compared effects on intestinal secretion in continuously fed and overnight fasted animals of the appetite regulating peptide orexin-A, the incretins glucose-dependent insulinotropic polypeptide (GIP) and glucagon like peptide-1 (GLP-1), and the established secretagogues vasoactive intestinal polypeptide (VIP) and serotonin. Methods: Lewis x Dark Agouti rats had free access to water and, unless fasted overnight, free access to food. Animals were anesthetized and a segment of proximal duodenum with intact blood supply cannulated in situ. Mucosal bicarbonate secretion was continuously recorded (pH stat) and compounds were administered to the duodenum by close intra- arterial infusion. Results: Infusion of orexin-A (60-600 pmol kg-1 h-1) stimulated the secretion and over-night food deprivation abolished secretory responses. Food deprivation also decreased mucosal OX1 and OX2 mRNA expression as well as OX1 protein. Infusion of GIP (60-600 pmol kg-1 h-1) caused dose-dependent increases in bicarbonate secretion in fed (p<0.01), but not in over-night fasted (p>0.05) animals. At a higher dose (6000 pmol kg-1 h-1), GLP-1 induced a slight increase (p<0.05) in secretion in fasted animals. In contrast, short term fasting did not affect secretory responses to VIP (50- 1000 pmol kg-1 h-1) or serotonin (20-200 nmol kg-1 h-1). Conclusions: The food dependence of secretory stimulation by orexin-A and GIP suggest interesting interactions between appetite regulation, body metabolism and intestinal function. The intact bicarbonate responses to VIP and serotonin indicate that short term food deprivation does not affect the secretory capacity of the duodenal mucosa in general.