Interaction of amiloride and hydrochlorothiazide with atrial natriuretic factor in the medullary collecting duct

Medullary collecting duct function was studied using the in vivo microcatheterization technique in three groups of rats receiving amiloride, hydrochlorothiazide, or both diuretics. In each group of animals, atrial natriuretic factor (ANF 99–126) was given in the second phase of the experiment. The combination of amiloride and hydrochlorothiazide resulted in a more marked natriuresis than either diuretic given as a single agent. Sodium reabsorption in the medullary collecting duct, as a fraction of the delivered load, was reduced from 64% (amiloride) and 69% (hydrochlorothiazide) to 29% (amiloride and hydrochlorothiazide). Atrial natriuretic factor reduced collecting duct sodium reabsorption when added to amiloride or hydrochlorothiazide to 23% and to 41%, respectively, but had no additional effect when given with amiloride and hydrochlorothiazide. Potassium excretion with amiloride and hydrochlorothiazide was intermediate between amiloride or hydrochlorothiazide given as single agents. With the diuretic c...