AJP - Renal Physiology, Vol 250, Issue 5 930-F941, Copyright © 1986 by American Physiological Society
Diurnal potassium excretory cycles in the rat
L. Rabinowitz, C. J. Wydner, K. M. Smith and H. Yamauchi
Diurnal potassium cycles (DPC) were measured in unanesthetized undisturbed
rats fed a liquid diet and maintained in a 12-h light-dark environment. A
fourfold step increase in diet potassium content increased DPC amplitude
without altering phase. After presentation of the high-potassium diet, the
initial adaptive increase in excretion occurred within 1.5 h (diet given
during dark phase) and within 6 h (diet given during light phase). On a day
when food was withheld (no potassium intake), DPC were present but with a
lowered amplitude. The amount of potassium excreted on a fasting day
exceeded gut and extracellular fluid potassium content and was only
modestly increased when rats were previously fed a high-potassium diet. In
adrenalectomized rats that received no steroid replacement or received
constant infusions of low levels of aldosterone, dexamethasone, or
aldosterone plus dexamethasone, potassium balance and DPC were normal. It
is concluded that the amplitude of DPC in the rat is determined in part by
the availability of potassium from both intracellular and extracellular
potassium pools; mechanisms independent of potassium intake can generate
the DPC; and the presence or the cyclic secretion of adrenal steroids is
not necessary for the generation of DPC in the rat.
