AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 2 510-R517, Copyright © 1989 by American Physiological Society
Amiloride effect on diurnal cyclic Na and K excretion in rats
P. L. Dalton and L. Rabinowitz
Department of Human Physiology, University of California School of Medicine, Davis 95616.
Amiloride was administered to rats during the peak and minimum of Na and K
diurnal rhythmic excretion (i.e., during early dark phase and early light
phase). In rats receiving a normal-K diet (2.34 meq/day) amiloride
decreased K excretion from 186 to 37 mueq/h (dark phase) and from 31 to 4
mueq/h (light phase). Amiloride increased Na excretion from 91 to 344
mueq/h (dark phase) and from 35 to 164 mueq/h (light phase). Rats receiving
a high-K diet (10.4 meq/day) showed a higher diurnal peak and minimum for K
excretion. During high-K intake, amiloride decreased K excretion from 787
to 191 mueq/h (dark phase) and from 197 to 40 mueq/h (light phase) and
increased Na excretion from 237 to 891 mueq/h (dark phase) and from 31 to
222 mueq/h (light phase). Whenever given, amiloride reduced K excretion to
approximately 20% of control excretion. It is concluded that rhythmic
changes in amiloride-sensitive distal transport are largely, but not
entirely, responsible for the diurnal K cycle, but do not cause the
concurrent Na cycle. Thus the diurnal cycles in Na and K are expressed
through changes in different transport mechanisms. In rats maintained on a
high-K diet there is an increase in rhythmic K secretion and Na
reabsorption by amiloride-sensitive transport. To maintain Na excretion
unchanged, Na reabsorption must be correspondingly depressed at an
amiloride-insensitive site.
