Stimulation of duodenal bicarbonate secretion by misoprostol

Graded doses of topical misoprostol were examined for effects on duodenal bicarbonate output in fasted conscious rats and compared with perfusions of the H₂-receptor blocker cimetidine. Chronic loops (2 cm) of the proximal duodenum were prepared in male Sprague-Dawley rats weighing 250 g. A thin perfusion tube was placed in the duodenal bulb, and a permanent cannula drained the distal end to the exterior. The stomach and remaining duodenum with biliary and pancreatic ducts were then reanastomosed. During tests, the loops were perfused with isotonic saline at 0.5 ml/min and samples of 15-min effluents analyzed for HCO₃^? using a modified back-titration method. Drugs and stimulants were added to the perfusion fluid. Misoprostol at 10^?10 M significantly (P<0.02) elevated the duodenal HCO₃^? from basal value (N=10), and concentrations of 10^?10 to 4×10^?4 M produced dose-dependent increases of bicarbonate secretion, with a peak output of 49±7 μmol/cm/hr. A peak response of the same magnitude, 42±4 μmol/cm/hr, is observed after 5-min exposure of the loops to 150 mm HCl. The response to a single dose of 10^?4 M misoprostol was sustained, similar to the prolonged stimulatory effects of 5-min acid exposure. Perfusions of the loop with graded natural PGE₂ result in similar increases of duodenal HCO₃^?, but the peak may be lower and the response to a single dose is less sustained. The H₂-receptor blocker cimetidine, perfused at concentrations of 10^?7 to 10^?4 M failed to affect duodenal, HCO₃^? output. Misoprostol was a potent stimulator of HCO₃^? output in the proximal duodenum of the conscious rat, and the response to a single dose was sustained. Peak outputs during misoprostol perfusion reached the same magnitude as observed after exposure of the loops to 150 mm HCl.