Cholecystokinin but not ghrelin stimulates mucosal bicarbonate secretion in rat duodenum: Independence of feeding status and cholinergic stimuli

• CCK-8 induces dose-dependent increases in duodenal alkaline secretion.
• Overnight fasting does not affect the response to CCK-8.
• Ghrelin does not affect the duodenal secretion.
• CCK-8 induces intracellular calcium signaling in duodenal enterocytes.
• CCK may be important in the rapid postprandial duodenal protection against acid.

Cholecystokinin (CCK) is an important regulator of food digestion but its influence on small intestinal secretion has received little attention. We characterized effects of CCK-8, ghrelin and some related peptides on duodenal HCO3− secretion in vivo and demonstrated CCK-induced calcium signaling in acutely isolated enterocytes.A segment of proximal duodenum with intact blood supply was cannulated in situ in anaesthetized rats. Mucosal HCO3− secretion was continuously recorded (pH-stat). Peptides were administrated to the duodenum by close intra-arterial infusion. Clusters of duodenal enterocytes were attached to the bottom of a perfusion chamber. The intracellular calcium concentration ([Ca2 +]i) was examined by dual-wavelength imaging.CCK-8 (3.0, 15 and 60 pmol/kg,h) caused dose-dependent increases (p < 0.01) in duodenal alkaline secretion in both overnight fasted and continuously fed animals. The CCK1R-antagonist devazepide but neither the CCK2R-antagonist YMM022 nor the melatonin MT2-selective antagonist luzindole inhibited the rise in secretion. Atropine decreased sensitivity to CCK-8. The appetite-related peptide ghrelin was without effect on the duodenal secretion in fasted as well as fed animals. Superfusion with CCK-8 (1.0-50 nM) induced [Ca2 +]i signaling in acutely isolated duodenal enterocytes. After an initial peak response, [Ca2 +]i returned to near basal values within 3–5 min. Devazepide but not YMM022 inhibited this [Ca2 +]i response.Low doses of CCK-8 stimulate duodenal alkaline secretion and induce enterocyte [Ca2 +]i signaling by an action at CCK1 receptors. The results point to importance of CCK in the rapid postprandial rise in mucosa-protective duodenal secretion.