1. The possibility of a Na+/H+ exchange mechanism in the presence of NaF (Bond & Hunt, 1956) has been studied in acid secreting and non-acid secreting stomachs of anaesthetized cats. 2. In non-acid secreting stomachs, although H+ loss and Na+ gain were both pH related, there was no constant relationship between the two. 3. The H+ loss in non-acid secreting stomachs could not account for the H+ loss in histamine stimulated stomachs. 4. In acid secreting stomachs the Na+ or neutral Cl- gain was only of the order of 50% of the H+ loss, and, in the presence of isosmolal NaNO3, NaF produced the same reduction in H+ but with a markedly suppressed gain in neutral chloride. 5. The NaF induced reduction in H+ output was accompanied by reductions in the total Cl- output, the K+ output and the mucosal blood flow. 6. It is concluded that the reduction in H+ output from histamine stimulated stomachs is largely a result of inhibition of secretion.
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