The potencies with which four adenosine deaminase-resistant analogs of adenosine affected the volume, pH and acid output of basal gastric acid secretions were examined in unanesthetized rats with chronic indwelling gastric cannulas. All four adenosine receptor agonists, R-phenylisopropyladenosine (R-PIA), S-phenylisopropyladenosine (S-PIA), N-ethylcarboxamide adenosine (NECA), and 2-chloroadenosine (CADO) significantly decreased gastric acid output in a dose-dependent manner. The rank order of potency was NECA, R-PIA > CADO > S-PIA. NECA and R-PIA were approximately equipotent in reducing gastric acid output. The levels of gastric acid output tended to increase at the lowest doses of the agonists. NECA decreased the volume of gastric secretion, whereas R-PIA had no effect on volume, but significantly increased the pH of the secretions. Valid measurements of pH in NECA-treated rats were not always obtainable because of near total inhibition of gastric secretions. S-PIA did not significantly affect volume, but increased pH at the higher doses tested. CADO decreased volume, but did not affect pH. These results indicate that adenosine analogs regulate not only the hydrogen ion concentration, but also the volume of gastric secretions.
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