Chronic sodium loading augments the natriuretic response to acute volume
expansion in the preweaned rat.
Muchant, Dianne G., Barbara A. Thornhill, David C. Belmonte, Robin A. Felder,
Alex Baertschi, Robert L Chevalier.
Department of Pediatrics, Department of Pathology, Department of
Physiology, University of Virginia, Charlottesville, Virginia 22908
APStracts 2:0015R, 1995.
Positive sodium (Na) balance is necessary for normal somatic growth of the
neonate, and the neonatal renal response to volume expansion (VE) is
attenuated compared to the adult. To test the hypothesis that dietary Na
modulates the developmental response to VE, preweaned rats were artificially
reared with either a normal (25 mEq/l) or high Na (145 mEq/l) diet for 7-8
days, and were compared to adult rats receiving normal or high Na. Serum Na
concentration remained normal in adults on high Na, whereas neonates became
hypernatremic. Glomerular filtration rate (GFR), urinary flow (V), and
urinary sodium (UNaV) were measured before and after acute saline VE (1% body
weight). While remaining constant in preweaned rats, GFR increased more than
50% in adult rats following VE (p<0.05). High Na intake augmented V and UNaV
following VE, but was not sustained in neonates as in adults. Plasma atrial
natriuretic peptide (ANP) and cyclic GMP excretion (UcGMPV) were measured:
baseline UcGMPV was lower in preweaned rats receiving normal Na, but
increased similar to adult levels following VE. Postexpansion plasma ANP was
higher in preweaned than adult rats, and was not affected by dietary sodium
regardless of age. We conclude that the attenuated postexpansion natriuresis
in the neonate is due in part to an adaptive response to limited sodium
intake. However, neonatal compensation to increased Na intake is incomplete,
and independent of plasma ANP.
Received 7 October 1994; accepted in final form 11 January 1995.
APS Manuscript Number R583-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative Comp.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 February 1995.