AJP - Renal Physiology, Vol 245, Issue 3 349-F358, Copyright © 1983 by American Physiological Society
Hydrogen ion secretion by the rat distal nephron: adaptation to chronic alkali and acid ingestion
C. Kornandakieti, R. Grekin and R. L. Tannen
Isolated rat kidneys perfused at a low bicarbonate concentration were
subjected to increased rates of buffer excretion, provided as creatinine,
in order to examine the maximal hydrogen ion secretory capacity of the
distal nephron. Preliminary experiments with kidneys from normal rats
indicated that the quantity of hydrogen ion that titrated creatinine from
urine pH to a pH of 6.0, designated TA-pH 6.0, provided an index of net
hydrogen ion secretion by a functional segment of the distal nephron. With
this technique the response of distal nephron hydrogen ion transport to
ingestion of both acid and alkali loads was examined. Perfused kidneys from
rats with chronic metabolic acidosis, produced by drinking 1.5% NH4Cl for
3-5 days, excreted urine with a lower pH and higher total titratable acid
and TA-pH 6.0 than appropriate controls. Perfused kidneys from rats that
ingested NaHCO3 for 7 days exhibited a higher urine pH and lower rates of
total titratable acid and TA-pH 6.0 than controls. By contrast, kidneys
from rats acutely tube-fed NaHCO3 3 h prior to study showed no change in
urinary acidification parameters. Thus, chronic ingestion of an acid load
stimulates, and chronic ingestion of an alkali load inhibits, the intrinsic
hydrogen ion secretory capacity of the rat kidney at a distal nephron site.
This intrinsic adaptation of the hydrogen ion transport mechanism is not
secondary to changes in aldosterone because rats that ingested NaHCO3
chronically had higher plasma aldosterone levels than controls.
