Effect of dietary salt on neuronal nitric oxide synthase in the
inner medullary collecting duct.
Roczniak, Agnes, Joseph Zimpelmann, and Kevin D. Burns.
Departments of Medicine and Cellular and Molecular Medicine,
University of Ottawa and Ottawa General Hospital, Ottawa, Ontario,
Canada K1H 8L6
APStracts 5:0060F, 1998.
Nitric oxide (NO) derived from neuronal NO synthase (nNOS) in the
kidney inner medulla has been implicated in the regulation of
arterial blood pressure. The purpose of the present study was to
determine the effect of high dietary NaCl on the expression of nNOS
in the rat inner medullary collecting duct (IMCD). After 3 days or 3
weeks of high (4.0%) NaCl diet in rats, urinary NO2-/NO3- excretion
significantly increased. In freshly microdissected IMCD, nNOS was
readily detected by immunofluorescence with polyclonal antibody, an
effect that was completely blocked by neutralization of antibody with
immunizing antigen. In rats fed a 4.0% NaCl diet for 3 days, IMCD
nNOS mRNA, detected by RT-PCR, did not change from control values
(0.3% NaCl: 19.84 +/- 1.57 x 103 vs. 4.0% NaCl: 20.44 +/- 3.14 x 103
cpm, P = NS, n = 3). By Western blotting however, nNOS protein
expression significantly increased (0.3% NaCl: 0.51 +/- 0.12 vs 4.0%
NaCl: 0.92 +/- 0.14 arbitrary units, P< 0.05, n = 5). After 3 weeks
of 4.0% dietary NaCl, expression of nNOS mRNA and protein in IMCD did
not differ significantly from control values. In contrast to these
data, renal cortical expression of nNOS mRNA and protein were
significantly decreased after 4.0% NaCl diet for 3 days. High dietary
NaCl had no significant effect on expression of mRNA for inducible NO
synthase (iNOS) in IMCD after either 3 days or 3 weeks. In summary,
our data indicate that nNOS mRNA and protein are expressed in IMCD
and that high dietary NaCl differentially regulates nNOS expression
in IMCD and cortex. The early increase in nNOS protein in IMCD may
contribute to enhanced local production of NO, and thereby represent
an adaptive response to salt intake.
Received 2 September 1997; accepted in final form 27 February
1998.
APS Manuscript Number F279-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 9 March 1998