Gastric and duodenal HCO3- transport in vivo: influence of prostaglandins

Abstract

Gastric and duodenal HCO3- transport was compared in the same mammalian species (cat) in vivo. The most appropriate technique for detecting HCO3- in the lumen of the stomach was measurement of pH and CO2 tension, whereas in the duodenum it was pH-stat titration. For experiments on gastric HCO3- transport, conscious cats prepared with vagally denervated fundic pouches were used; for those on duodenal transport anesthetized animals with in situ perfused segments were studied. When expressed in terms of gross surface area, basal HCO3- output was six times greater in the duodenum than in the stomach (approximately 1.5 cf. approximately 0.25 mumol X cm-2 X 15 min-1). topical application of 16,16-dimethyl prostaglandin E2 (dmPGE2) to duodenal mucosa caused a concentration-dependent increase in HCO3- output and transmucosal electrical potential difference (PD) over the range 0.01–1.0 microgram X ml-1. PGE2 was approximately 200 times less potent than dmPGE2 as a stimulant of duodenal HCO3- transport. Increases in the rate of luminal HCO3- output following application of dmPGE2 were considerably less in the stomach compared with the duodenum (approximately 50% cf. approximately 1,000% at 1 microgram X ml-1). Intravenous dmPGE2 (1 microgram X kg-1 X h-1) had no effect on either gastric or duodenal HCO3- outputs. Indomethacin (5 mg X kg-1 iv) inhibited duodenal HCO3- output by approximately 50% and reduced PD but did not influence gastric HCO3- output. We propose that in the cat duodenum in vivo local prostaglandins regulate HCO3- transport, but in the cat stomach in vivo they have a less important role.