AJP - Renal Physiology, Vol 253, Issue 6 1178-F1181, Copyright © 1987 by American Physiological Society
Plasma potassium and diurnal cyclic potassium excretion in the rat
L. Rabinowitz, R. Berlin and H. Yamauchi
Department of Human Physiology, University of California School of Medicine, Davis 95616.
The relation of the plasma potassium concentration to the daily cyclic
variation in potassium excretion was examined in undisturbed,
unanesthetized male Sprague-Dawley rats maintained on a liquid diet in a
12-h light-dark environment. Potassium excretion increased from a
light-phase minimum of 16 mu eq/h to a peak of 256 mu eq/h 3 h after the
beginning of the dark phase. Plasma potassium concentration in arterial
blood, sampled in rats at 90-min intervals during these changes in
potassium excretion, showed no significant change and was in the range
4.50-4.99 meq/liter. In adrenalectomized rats receiving aldosterone and
dexamethasone at constant basal rates by implanted pumps, the daily cycle
of potassium excretion was the same as in the intact rats, and plasma
potassium was not significantly different when measured at the time of
minimum and maximum rates of potassium excretion (4.79 +/- 0.42 vs 5.16 +/-
0.47 meq/liter, mean +/- SD). These results indicate that plasma potassium
concentration is not the efferent factor controlling diurnal cyclic changes
in potassium excretion in adrenal intact rats and may not be the only
significant factor in adrenalectomized-steroid replaced rats.
