AJP - Renal Physiology, Vol 253, Issue 6 1182-F1196, Copyright © 1987 by American Physiological Society
Kaliuretic regulatory factors in the rat
J. C. Rutledge and L. Rabinowitz
Department of Internal Medicine, University of California School of Medicine, Davis 95616.
To evaluate the role of aldosterone, plasma potassium, and sodium and urine
excretion rates in controlling both total daily potassium excretion and the
diurnal cyclic excretion of potassium, we performed experiments on
unanesthetized, undisturbed rats kept in a 12-h light/12-h dark environment
and fed a liquid diet. Independent variations were imposed on potassium
intake, sodium intake, and, in groups of adrenalectomized rats, on
aldosterone infusion rates. Potassium intake was 2.6, 10.6, and 18.7
meq/day. Sodium intake was 2.1, 6.7, and 17 meq/day. Aldosterone infusion
was 0.1, 0.4, 1, and 10 times a basal rate of 1 microgram.day-1.100 g-1,
with constant dexamethasone infusion at 1.43 micrograms.day-1.100 g-1.
Twenty-four-hour excretion of potassium and sodium balanced 24-h intake of
potassium and sodium regardless of the imposed combination of known
regulatory factors. The amplitudes of potassium and sodium excretion during
the diurnal cycle were each closely related to the ongoing levels of
potassium and sodium intake. Plasma potassium was measured at the peak of
the potassium cycle. It is suggested, based on analysis of the results,
that when caloric balance was maintained, the amplitude of the diurnal
potassium cycle was not importantly influenced by the rates of sodium and
urine excretion, and, in addition to effects of aldosterone and plasma
potassium concentration, the amplitude was importantly influenced by
unspecified, homeostatically effective kaliuretic factors. Adrenalectomized
rats receiving subbasal aldosterone replacement rejected the high potassium
diet, were anuric, lost weight, and were severely hyperkalemic,
observations indicating the necessity of adequate aldosterone for
maintenance of potassium homeostasis.
