EFFECT OF OMEPRAZOLE ON SODIUM AND POTASSIUM OUTPUT IN PENTAGASTRIN-STIMULATED EQUINE GASTRIC CONTENTS

Objective-To better characterize the source of the large nonparietal s ecretory response to pentagastrin (PG) expressed in gastric contents o f cannulated horses. Animals-Adult cross-bred horses: 4 geldings and 1 mare. Procedure-Horses were prepared by surgical insertion of a silas tic gastric cannula from which gastric contents after feed was withhel d could be continuously collected by gravity drainage. During experime nts, the horses were lightly restrained in stocks, the gastric cannula was opened, and a catheter was inserted into a jugular vein. Over the next 5 hours, gastric contents were collected in 15-minute aliquots f or which volume, pH, [Na+], and [K+] were measured. During the first h our, treatment was not administered. At the start of the second hour, either 0.5 mg of omeprazole (OME; dissolved in glycerol formal)/kg of body weight, or 0.9% NaCl (PSS) of comparable volume, was given IV at random as a bolus, At the start of the third hour, IV infusion of PG ( 6 mu g/ kg/h) was started and continued for the next 2 hours. Results- The response to PG in the PSS-treated horses was similar to that previ ously seen-significant decrease in pH and increase in volume of gastri c contents, and no change in [K+] and [Na+], but a modest volume-relat ed increase in their respective outputs. After OME treatment, pH of th e contents increased sharply and remained between 5 and 6 throughout P G infusion Sodium concentration significantly increased after OME and virtually paralleled the pH response throughout the rest of the experi ment; volume of gastric contents significantly increased in response t o PG infusion and resulted in a significant increase in Na output. The re was no change in K output in OME-treated animals. Conclusions-PG in duces a marked, nonparietal, secretory response into the gastric conte nts of cannulated horses. The volume and [Na+] of this response was ma intained after pretreatment with OME, although the pH of the contents became basic, indicating that this nonparietal response is not mediate d by an OME-sensitive proton pump.