Compensatory adaptation of sodium and bicarbonate excretion: effect of diuretics.

Complete clamping of the contralateral kidney results in a rapid and significant increase in the fractional excretion of Na, K, and bicarbonate by the remaining kidney during bicarbonate loading. Similar studies were performed in dogs after administration of diuretics with different major sites of action to localize the adaptive excretory response to acute reduction in renal mass. Volume expansion was carefully avoided. In experiments with the loop inhibitor, furosemide, contralateral kidney clamping rapidly and significantly increased fractional excretion of Na and bicarbonate. A more delayed and smaller response was observed in dogs given hydrochlorothiazide. Acetazolamide, a potent inhibitor of proximal Na bicarbonate reabsorption, completely blocked the excretory response to contralateral kidney clamping. The enhanced response with furosemide and its blockade with acetazolamide indicates a proximal site of adaptation to acute contralateral kidney exclusion. The overall natriuretic response depends on the level of inhibition of loop reabsorption.