AJP - Renal Physiology, Vol 250, Issue 3 551-F558, Copyright © 1986 by American Physiological Society
Body sodium in rats: response to DOCA, adrenalectomy, changes in salt intake, and a salt load
F. O. Simpson, J. M. Ledingham, J. M. Paulin and R. D. Purves
Body Na was studied by an isotope method in rats on Na-free diet plus a
choice of H2O and 0.5% or 0.1% NaCl. Two groups (1 on 0.5%, 1 on 0.1% NaCl)
had Silastic deoxycorticosterone acetate (DOCA) implants, two similar
groups were sham operated, and a fifth group (on 0.5% NaCl) underwent
adrenalectomy (ADX). Saline consumption increased in DOCA-treated and ADX
rats. Body Na was increased by DOCA and by drinking 0.5% NaCl compared with
0.1% NaCl. Body Na after intraperitoneal NaCl loading (which raised body Na
8-10%) and withdrawal of NaCl drinking fluids was analyzed by use of the
model y = Ae-a(t-d) + Be-bt, where y is body Na at time t and d is delay
before fast rate constant a is established; d was greater on the lower Na
intake. Rate constant a was not reduced by chronic DOCA treatment.
Coefficient B of the slow exponential, representing the basal level to
which body Na falls on zero Na intake, and equivalent to Hollenberg's
"set-point," was higher in DOCA-treated rats. This analysis makes use of
Hollenberg's set-point concept, but the findings suggest that the set-point
is related to mineralocorticoid activity and is thus presumably variable.
