Back-diffusion of CO2 and its influence on the intramural pH in gastric mucosa.

We have examined the back-diffusion of CO2 generated by buffering HCI with NaHCO, in the stomach, observed its influence on the pH in the wall of the gastric mucosa, and compared its effects with those of HCl. Isolated stomachs of 17 anesthetized dogs were exposed to either ( I ) 250 ml NaCl at pH 7, or (2) 125 ml HCl (12.5 meq) + 125 ml NaHCO, (12.5 meq) to generate 12.5 meq CO2 in the stomach, or (3) 250 ml HCI alone to give either 12.5 or 35 meq HCl in the stomach. Samples of gastric fluid and arterial blood were collected every 20 min for 6 hr and analyzed for pH and pC02. The intramural pH of the gastric wall was measured by hollow viscus tonometry. The pC02 in gastric juice rose to 1184 + 139 mm Hg upon the generation of CO2 in the stomach. The till of the CO2 generated by the buffering of acid was 32 + 4 min and of the pC02 was 18.7 f 0.7 min. The till of an equimolar amount of HCI was 2 hr 42 min f 40 min. The disappearance of the CO, was accompanied by a rise in intragastric pH from 6.0 f 0.01 to 6.8 + 0.09 (P < 0.05). and by a fall in intramural pH in the gastric wall from control values of 7.31 + 0.05 to 6.3 f 0.8 (P .Z 0.001). In contrast the pH in gastric fluid did not change and the pH in the intramural fluid did not fall below control values following the administration of 12.5 or 35 meq HCI alone.