Effect of omeprazole on sodium and potassium output in pentagastrin-stimulated equine gastric contents.

OBJECTIVE

To better characterize the source of the large nonparietal secretory response to pentagastrin (PG) expressed in gastric contents of cannulated horses.

ANIMALS

Adult cross-bred horses: 4 geldings and 1 mare.

PROCEDURE

Horses were prepared by surgical insertion of a silastic gastric cannula from which gastric contents after feed was withheld could be continuously collected by gravity drainage. During experiments, 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 for which volume, pH, [Na+], and [K+] were measured. During the first hour, 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 micrograms/ 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 previously seen-significant decrease in pH and increase in volume of gastric contents, and no change in [K+] and [Na+], but a modest volume-related increase in their respective outputs. After OME treatment, pH of the contents increased sharply and remained between 5 and 6 throughout PG infusion. Sodium concentration significantly increased after OME and virtually paralleled the pH response throughout the rest of the experiment; volume of gastric contents significantly increased in response to PG infusion and resulted in a significant increase in Na output. There was no change in K output in OME-treated animals.

CONCLUSIONS

PG induces a marked, nonparietal, secretory response into the gastric contents of cannulated horses. The volume and [Na+] of this response was maintained after pretreatment with OME, although the pH of the contents became basic, indicating that this nonparietal response is not mediated by an OME-sensitive proton pump.