Adaptation to chronic potassium loading in normal man.

To analyze factors involved in the maintenance of potassium balance during increased intake, 6 healthy males were studied on a normal (80 mEq) and high (300 mEq) potassium diet. After 18 days of potassium-rich diet, urinary potassium excretion had increased from 50 +/- 12 to 233 +/- 45 mEq/day. Plasma renin activity and body weight were unchanged, serum potassium and plasma aldosterone somewhat increased, and the ratio of plasma aldosterone to renin activity consistently elevated. Acetazolamide injection (1 g i.v.) increased sodium and potassium excretion rates equally on the two diets indicating that a sudden increase in distal solute delivery was not handled differently after potassium loading. The reaction to a high dose of aldosterone (1 mg i.v. followed by 0.5 mg/h infusion) in terms of sodium retention and potassium excretion was also comparable, indicating no altered sensitivity to aldosterone after adaptation to the potassium-rich diet. By contrast, the aldosterone antagonist canrenoate (100 mg i.v.) acutely raised NaCl excretion without changing the potassium excretion during the high potassium diet, but did not affect NaCl excretion during the normal diet. Subsequent oral administration of spironolactone for 5 days (200 mg daily) caused a more negative sodium balance associated with more weight loss and rise in renin activity during the potassium rich diet. Surprisingly we noticed no fall in renal potassium excretion in this period, but mean serum potassium was raised by 0.3-0.4 mEq/l at the end. These results suggest that adaptation of a healthy subject to a potassium-rich diet does not involve intrinsic changes of the distal tubule, but a shift of sodium reabsorption from a proximal to a distal (aldosterone-sensitive) nephron level.(ABSTRACT TRUNCATED AT 250 WORDS)