AJP - Renal Physiology, Vol 248, Issue 4 602-F606, Copyright © 1985 by American Physiological Society
Potassium excretion by the isolated perfused kidney from the potassium-adapted rat
W. R. Adam and B. A. Adams
Adaptation to a high potassium diet leads to an enhanced ability to excrete
an acute potassium load. The aim of this study was to examine whether the
enhanced kaliuretic ability is an intrinsic renal adaptation or is
secondary to extrarenal mediators such as aldosterone. Kidneys from control
rats and rats on a high potassium diet were isolated and perfused in a
cell-free medium (glomerular filtration rate 0.5 ml/min, fractional sodium
reabsorption 95%). Feeding in the 24 h prior to perfusion had a profound
effect on fractional K+ excretion in rats on high K+ (fed 1.4 +/- 0.11,
fasted 0.70 +/- 0.07) but not in control (fed 0.59 +/- 0.05, fasted 0.64
+/- 0.05) rats. After feeding but not fasting, rats on high K+ had a
greater fractional K+ excretion than control K+ rats. Spironolactone
inhibited fractional K+ excretion in fed rats on high K+ but not in control
rats (high K+ 1.45 +/- 0.18, high K+ + spironolactone 0.95 +/- 0.15;
control 0.59 +/- 0.05, control + spironolactone 0.46 +/- 0.02). Although
these experiments do not exclude an intrinsic renal adaptation in potassium
excretion, a major component of the increased potassium excretion relates
to the increased potassium intake, probably mediated via aldosterone.
