Effect of graded doses of intraluminal H+, prostaglandin E2, and inhibition of endogenous prostaglandin synthesis on proximal duodenal bicarbonate secretion in unanesthetized rat.

The purpose of this study was to examine the effect of graded doses of intraluminal HCl and prostaglandin E2 on proximal duodenal bicarbonate secretion in unanesthetized rats. Basal bicarbonate secretion was approximately 14 mumol/cm . h and increased significantly in a dose-related manner to 50, 100, and 150 mM HCl as follows: 22.0 +/- 1.5, 29.2 +/- 4.0, and 42.0 +/- 4.3 mumol/cm . h, respectively (mean +/- SE). After a single 5-min infusion of 150 mM HCl, duodenal bicarbonate secretion remained significantly above basal for almost 3 h. The responses to 100 mM HCl and 10(-4) M prostaglandin E2 were similar (29.2 +/- 4.0 and 26.9 +/- 4.4 mumol/cm . h, respectively). Indomethacin (4 mg/kg, intraperitoneally) suppressed the bicarbonate response to 150 mM HCl; whereas the response to 10(-4) M prostaglandin E2 was unaltered. These studies in the in vivo rat indicate that (a) graded doses of intraluminal HCl produced graded increases in proximal duodenal bicarbonate secretion; (b) the bicarbonate output in response to a 5-min infusion of HCl persisted for almost 3 h; and (c) the bicarbonate response to HCl was essentially abolished by indomethacin pretreatment, suggesting that endogenous prostaglandins are at least in part involved in acid-induced proximal duodenal bicarbonate secretion.