IMPORTANCE OF VAGUS NERVES IN DUODENAL ACID NEUTRALIZATION IN ANESTHETIZED PIGS

During the cephalic phase of gastric acid secretion, vagally mediated synchronous stimulation of bicarbonate provides protection against the acid. The purpose of this study was to determine simultaneously the e ffect of electrical vagal stimulation (EVS) on pancreatic, hepatic, an d duodenal mucosal bicarbonate secretion, thereby estimating their rel ative importance in vagally induced duodenal acid neutralization. Spla nchnicotomy increased vagally induced pancreaticobiliary bicarbonate s ecretion, whereas duodenal mucosal bicarbonate secretion was unchanged . After splanchnicotomy, EVS (10 ms, 15 mA, 12 Hz) significantly incre ased pancreatic bicarbonate secretion (0-4.17 mmol/h), hepatic bicarbo nate secretion (0.16 to 0.22 mmol/h), and duodenal mucosal bicarbonate secretion (0.17 to 0.31 mmol/h). Pancreaticobiliary bicarbonate secre tion was atropine resistant, whereas vagally induced duodenal mucosal bicarbonate secretion was diminished by atropine (2.0 mg/kg). After sp lanchnicotomy, EVS (10 ms, 15 mA, 12 Hz) had no effect on portal plasm a concentration of secretin, whereas vasoactive intestinal peptide was increased (14-29 pM). EVS at 12 Hz with varying duration (3 or 10 ms) and amplitude (3-50 mA) had no further effect on the bicarbonate secr etion from the three organs. In addition, biliary [C-14]mannitol clear ance was shown not to be a reliable marker of canalicular bile secreti on in pigs. These results suggest that in the anesthetized pig 1) vaga l stimulation is only of minor importance to hepatic bicarbonate secre tion; 2) vagal stimulation activates pancreatic bicarbonate secretion through both cholinergic muscarinic and noncholinergic transmission; a nd 3) vagal stimulation induces duodenal mucosal bicarbonate secretion mainly through cholinergic muscarinic transmission. In conclusion, th ese results suggest that only pancreatic and duodenal bicarbonate prod uction play a role in vagally induced duodenal acid neutralization.