AJP - Renal Physiology, Vol 260, Issue 5 680-F687, Copyright © 1991 by American Physiological Society
Effects of chronic hyperkalemia on renal production and proximal tubule transport of ammonium in rats
T. D. DuBose Jr and D. W. Good
Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550.
Free-flow micropuncture experiments were performed to examine directly the
effects of chronic hyperkalemia on renal ammonium production, urinary
ammonium excretion, and proximal convoluted tubule ammonium transport in
the rat in vivo. Munich-Wistar rats were pair-fed either a control or a
high-K+ diet for 6-11 days. Chronic K+ loading was associated with an
increase in plasma K+ concentration and significant systemic metabolic
acidosis. Renal blood flow did not differ in control and high-K+ rats. In
the hyperkalemic rats, urinary ammonium excretion was reduced by 40% and
whole kidney ammonium production was reduced by 50% compared with controls.
In contrast, chronic hyperkalemia had no significant effect on net ammonium
transport by either the early or late segment of the proximal convoluted
tubule. Chronic hyperkalemia also had no effect on the absolute rate of
ammonium delivery to early or late proximal convoluted tubule sites. These
results indicate that a change in renal ammonium production does not
necessarily correlate with a change in proximal tubule ammonium transport
and that reduced urinary ammonium excretion in chronic hyperkalemia is not
due to impaired secretion of ammonium by the proximal convoluted tubule.
Chronic hyperkalemia may reduce ammonium excretion by decreasing transfer
of ammonium from proximal tubules to collecting ducts in the renal medulla.
