Cephalic Phase of Gastroduodenal Alkaline Secretion

This study was designed to determine gastric alkaline secretion (GAS) and duodenal alkaline secretion (DAS) and their relation to the duodenal motility pattern in conscious dogs under basal conditions and after vagal stimulation by sham-feeding and insulin hypoglycaemia. GAS was measured in the gastric perfusate and DAS was determined in the perfusate of the upper duodenum (7 cm in length between occluding balloons). Resting GAS and DAS showed typical periodicity in phase with myoelectric and motor activity, reaching peaks during phases II and III, respectively, and nadir during phase I of the migrating motor cycle (MMC). Vagal excitation by sham-feeding or insulin hypoglycaemia resulted in an immediate rise in GAS and DAS, accompanied by a suppression of MMC. Atropine (25 ug/kg) reduced basal GAS and DAS by about 50% and abolished GAS but not DAS in response to vagal stimulation, being accompanied by complete suppression of MMC for several hours. Following injection of indomethacin (2.5 mg/kg) to suppress the generation of endogenous prostaglandins, a prolonged reduction in basal GAS and DAS and an increase in the myoelectric activity and the disruption of the MMC occurred. Neither GAS nor DAS responses to vagal stimulation were affected by indomethacin. We conclude that resting GAS and DAS fluctuate cyclically in phase with gastroduodenal motor activity, and that vagal excitation results in a potent stimulation of alkaline secretion and myoelectric activity which are, in part, cholinergic and do not depend upon the generation of endogenous prostaglandins.