Determination of bicarbonate output using pH deflection in the rat duodenum: influences of prostaglandins and cholinergic agents.

We set up a system to measure the luminal pH, potential difference (PD) and bicarbonate output in the anesthetized rat duodenum, and investigated these responses caused by prostaglandins (PGs) and cholinergic agents. When the proximal duodenum (1.7 cm) was perfused at a flow rate of 0.7 ml/min with saline adjusted to pH 4.5, the duodenal pH, PD and HCO3- output were 5.5 to 6.0, -4 to -6 mV and 1.2 to 1.6 muEq/10 min, respectively; they were markedly reduced by i.v. injection of saturated KCl. Both natural (PGE1, PGE2) and synthetic (PGE2, PGl2) PGs, given either s.c. or i.v., significantly elevated all these parameters, while indomethacin (s.c.) decreased the pH as well as the PD. Small but significant increases of the pH were observed after i.v. administration of cholinergic agents (carbachol, bethanechol), a GABAergic agent (baclofen) and an analogue of thyrotropin releasing hormone (YM-14673), with a temporal elevation of the PD; the degree of net HCO3- output caused by these agents was 20-50% of the values obtained with PGE2 (100 micrograms/kg, i.v.), and they were significantly reduced in the presence of atropine. These results suggest that (a) the system using pH deflections can be used to sensitively detect HCO3- output in the rat duodenum, and (b) duodenal acid neutralizing capacity may be regulated by central and peripheral cholinergic systems as well as endogenous PGs.