Urine acidification in men

Distal renal tubular acidosis is often diagnosed using NH4Cl loading. More
recently this test has been replaced by the furosemide fludrocortison test (FF
test). The FF test is based on the classical mechanism that furosemide induces
distal tubular sodium delivery and fludrocortison further enhances sodium
re-absorption through ENaC and secondly H+ secretion through
H+-ATPase/H+-K+-ATPase in the collecting duct. In mice however, furosemide can
also acidify urine by stimulating the Na+-H+ transporter NHE3 and hereby Na+
reabsorption and H+ excretion. If such a mechanism is present in men as well,
the FF test could result in normal urinary acidification in patients with dRTA.

to determine if there is an alternative mechanism for urine acidification in
men in response to furosemide other than that through ENaC

an intervention study in which 10 healthy volunteers will undergo two
furosemide fludrocortison tests on separate days: one without and the other
after pre-treatment with the ENaC blocker amiloride (10 mg) which is given 2
hours before the start of the test.

The total number of blood samples is 3 per test. The total number of urine
samples is 5 per test. The risks of the study are negligible.