AJP - Renal Physiology, Vol 251, Issue 3 454-F459, Copyright © 1986 by American Physiological Society
Effect of dietary NaCl on chloride uptake in rat collecting duct segment
J. H. Galla, D. N. Bonduris, K. A. Kirk and R. G. Luke
To explore further the mechanism of the effect of dietary NaCl intake on
collecting duct (CDS) chloride uptake, we compared late distal chloride
delivery to and urinary 36Cl recovery (the latter as an index of
unidirectional efflux) from the CDS in four groups of male Sprague-Dawley
rats. Groups were prepared for 7-10 days as follows: group 1, drinking 0.15
M NaCl; group 2A, regular diet; group 2B, regular diet plus
deoxycorticosterone (2 mg im) (at 24 and 2 h before micropuncture); and
group 3, low-NaCl diet. To increase tubule fluid flow rate and produce
natriuresis without chloruresis, 0.15 M NaHCO3 at 5% body wt/h was infused
in all groups except group 3, in which an infusion of 150 mM Na+, 55 mM
Cl-, and 85 mM HCO3- was required to maintain a plasma chloride
concentration equal to that in other groups. Plasma chloride concentration
and arterial pH did not differ between groups before infusion. Urinary 36Cl
recovery increased in parallel with dietary NaCl content (P = 0.0001). By
analysis of multiple covariances, neither tubule fluid chloride
concentration nor chloride delivery to the CDS correlated with urinary 36Cl
recovery within any of the groups or for all animals studied. High doses of
mineralocorticoid did not alter chloride uptake in group 2. These data
suggest that progressive restriction of dietary NaCl enhances chloride
uptake in the CDS of the rat unrelated to changes in plasma chloride
concentration or chloride delivery from the superficial late distal
tubules.
