Determination of gastroduodenal alkaline responses in the rat

We set up a new system for measuring the gastroduodenal HCO₃⁻ responses using pH change and potential difference (PD) in the anesthetized rat. The stomach or the proximal duodenum was perfused at the flow rate of 0.7 mL/min with saline (pH 4.5), the pH of the perfusate and PD were continuously monitored, and HCO₃⁻ output was determined by back-titrating the perfusate and by measuring the area of pH change. In the case of the stomach, acid secretion was inhibited by omeprazole (60 mg/kg, i.p.). Output of both pH and HCO₃⁻ in these tissues was significantly increased by intravenous administration of prostaglandin (PGE₂), 16, 16-dimethyl PGE₂, carbachol, and YM-14673 (a thyrotropin-releasing hormone (TRH) analog), whereas the PD responded to these agents by a significant rise in the duodenum and decrease in the stomach. These parameters also responded to physiological stimulation such as mucosal acidification. When the area of pH change caused by various agents was plotted against the net amount of HCO₃⁻ output determined from back-titration, a significant relationship was found between these two factors (r = 0.98). These results indicate that this system using pH change may be useful for quantitative determination of HCO₃⁻ response in the gastroduodenal mucosa.