AJP - Renal Physiology, Vol 253, Issue 4 642-F648, Copyright © 1987 by American Physiological Society
Load dependency of sodium chloride reabsorption by medullary collecting duct in rat
W. A. Cupples and H. Sonnenberg
Department of Physiology, University of Toronto, Ontario, Canada.
During antidiuresis, the medullary collecting duct (MCD) reabsorbs sodium
in load-dependent fashion. However, attempts to characterize reabsorption
when sodium delivery to the MCD is elevated have not led to clear results,
largely due to interfering effects of the strategies employed to raise
delivery. In the present study, microcatheterization was performed in rats
undergoing water diuresis induced solely by infusion of 2.5% dextrose in
water, and in rats where solute delivery to the MCD was markedly elevated
by the combination of water diuresis with acute potassium chloride loading.
The results show that delivery of sodium was elevated by the experimental
maneuvers, averaging 7.01 +/- 0.83 mumol . min-1 . g kidney wt-1 compared
with a normal antidiuretic value in the literature of 3.50 +/- 0.40 mumol .
min-1 . g-1. Sodium and chloride reabsorptions were increased
proportionally, indicating that the MCD has a large capacity to transport
sodium chloride. Normalized sodium reabsorption remained high, varying in
different series between 80 +/- 10 and 96 +/- 1% of the delivered load.
Thus the MCD reabsorbed an average of 6.37 +/- 0.70 mumol . min-1 . g-1 of
sodium while sodium excretion was 0.52 +/- 0.11 mumol . min-1 . g-1. The
results emphasize the importance of MCD sodium chloride reabsorption for
determination of final urinary salt excretion, and thus for regulation of
body salt balance.
