AJP - Renal Physiology, Vol 241, Issue 3 250-F256, Copyright © 1981 by American Physiological Society
Dissociation of saline-induced natriuresis from urea washout in the rat
F. J. Gennari, C. Johns, C. R. Caflisch and S. Cortell
Medullary urea washout has been postulated to play a major role in the
natriuretic response to volume expansion (VE). To examine this hypothesis,
renal tissue solute composition was measured in a natriuretic and
nonnatriuretic model of VE. Renal tissue composition was analyzed during
hydropenia, acute VE, acute VE with renal artery pressure reduced to 70
mmHg at the onset of saline loading (immediate clamping), and acute VE with
renal artery pressure reduced to 70 mmHg after 45 min of saline loading
(delayed clamping). Immediate clamping, a nonnatriuretic model of VE,
prevented VE-induced urea washout and the increase in sodium and water
content in the cortex and outer medulla. Delayed clamping, a natriuretic
model of VE, produced a pattern of tissue composition very similar to
immediate clamping. Tissue urea content was not significantly different in
the two protocols and only minor differences in sodium and water content
were noted. Thus, under these experimental conditions, VE-induced
natriuresis can be dissociated from medullary urea washout, and other
mechanisms must be invoked to explain the increased sodium excretion.
