Low-dose PGE2 mimics the duodenal secretory response to luminal acid in mice

Luminal exposure to concentrated acid, the most accepted physiological stimulus for duodenal bicarbonate secretion (DBS), cannot be used with in vitro preparations due to potential tissue damage. We thus examined whether exposure to PGE(2), a well-characterized physiological duodenal secretagogue, could mimic the effects of acid perfusion. DBS was measured in C57/BL mice by pH-stat/back-titration and measurement of total dissolved CO2 concentration ([CO2](t)). Anion transport inhibitor DIDS, anion channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), carbonic anhydrase inhibitor methazolamide, and nonselective cyclooxygenase inhibitor indomethacin were used to inhibit separate components of HCO3- secretory pathway. Baseline DBS was not altered by exposure to methazolamide (0.1 mM) but was slightly reduced by DIDS (0.5 mM). DBS and [CO2](t) increased after acid and PGE(2) exposure. DIDS ( 0.5 mM) and NPPB (0.2 mM) abolished acid-induced DBS increase. Methazolamide ( 0.1 mM) and DIDS inhibited acid-induced [CO2](t) increase. DIDS, NPPB, or methazolamide had little effect on DBS in response to high concentration PGE(2) (100 mug/ml). Low concentration PGE(2) (1 mug/ml) increased DBS that was inhibited by DIDS, NPPB, and methazolamide. Pretreatment with indomethacin (5 mg/kg) inhibited DBS induced by acid exposure but not by PGE(2). High-dose PGE(2) substantially increases DBS by a mechanism that appears to be different than secretory response to luminal acid perfusion. Secretory response to low-dose PGE(2), at least in terms of inhibitor profile, closely resembles secretion in response to perfusion of physiological acid concentrations and may be a useful stimulus for in vitro study of DBS in isolated mouse duodenum.