AJP - Renal Physiology, Vol 245, Issue 3 329-F338, Copyright © 1983 by American Physiological Society
Demonstration of an intrinsic renal adaptation for K+ conservation in short-term K+ depletion
D. B. Ornt and R. L. Tannen
Renal potassium conservation occurs within 3 days of potassium deprivation
by a mechanism that appears to be independent of mineralocorticoids and
sodium and anion excretion. To examine whether the mechanism involves an
intrinsic renal adaptation, urinary potassium excretion was measured in
isolated perfused kidneys from rats maintained on a normal or K+-free diet
for 3 days. Perfusions were carried out with a K+ concentration that
averaged 3.5 mM and with glucose (5 mM) as the only substrate. Both
absolute (UKV) and fractional K+ excretion (FEK) were substantially less in
kidneys from animals on K+-free diets compared with controls. These
differences in K+ excretion were not explained by changes in GFR, urine
flow rate, urine pH, or sodium, chloride, or ammonium excretion. The K+
content of renal tissue was not different in the perfused and nonperfused
kidneys from rats receiving K+-free diets compared with controls.
Suppression of K+ excretion by amiloride (10(-4) M) suggested that, as in
vivo, tubular secretion of K+ in the perfused normal kidney accounts for
90% of the urinary K+ excretion and that tubular K+ secretion is reduced in
isolated kidneys from animals on a K+-free diet. Further studies of
isolated kidneys from adrenalectomized (ADX) rats receiving aldosterone and
dexamethasone replacement and fed a normal or K-free diet also revealed
significantly lower UKV and FEK in kidneys from animals on K+-free diets.
K+ content of renal tissue was not different in the ADX animals on a
K+-free diet compared with ADX rats on normal K+ intake. These studies
indicate that within 72 h of dietary K+ deprivation an intrinsic renal
adaptive process to conserve potassium is activated that is independent of
renal potassium content, aldosterone, and urinary factors that can alter K+
excretion such as flow, pH, ammonium, sodium, and anions. This regulatory
mechanism, which has a substantial influence on potassium excretion,
remains to be elucidated.
