Response to: “Is an increase in duodenal bicarbonate concentration after STa really enhanced bicarbonate ion secretion?”

may be that addition of 1 mM amiloride in the authors’ experiments did nothing to NHE:3 activity, and thus subsequent addition of guanylin inhibited NHE:3 activity to the same extent, as if no amiloride had been added. The pharmacological point might have been carried if first the authors had shown that 1 mM amiloride had reduced hydrogen ion secretion by measuring luminal acidification, but they did not offer this evidence. The comparison was guanylin with and without amiloride with no positive control that amiloride was effective in inhibiting hydrogen ion secretion on its own. In conclusion, while this is an interesting paper that shows that STa also acts in the duodenum, I believe it does not yet allow the distinction to be made between enhanced bicarbonate secretion and reduced hydrogen ion secretion. REFERENCES