T. Ogawa et al., TISSUE-SPECIFIC REGULATION OF RENAL AND CARDIAC ATRIAL-NATRIURETIC-FACTOR GENE-EXPRESSION IN DEOXYCORTICOSTERONE ACETATE-SALT RATS, Hypertension, 30(6), 1997, pp. 1342-1347
Atrial natriuretic factor (ANF) is expressed in several noncardiac tis
sues where it may have an autocrine or paracrine function. Such functi
on may be expected of locally synthesized ANF in the renal parenchyma.
Previous investigations of the existence of ANF mRNA in the renal par
enchyma have yielded conflicting results. The investigations reported
here were designed to detect and measure ANF mRNA in normal rats and i
n rats subjected to a deoxycorticosterone acetate (DOCA)-salt treatmen
t schedule known to strongly activate cardiac ANF gene expression. The
expression of the renal ANF gene was measured using a newly developed
quantitative competitive reverse transcription-polymerase chain react
ion (QC-RT-PCR). This method uses an internal competitor that serves a
s an internal standard and makes the procedure independent of measurem
ent relative to housekeeping genes. It was found that renal ANF mRNA l
evels were 10(7) times lower than those found in left or right atria,
but immunoreactive (ir) renal ANF concentration by specific radioimmun
oassay was 10(4) times lower than that of atrial irANF levels. Reverse
-phase high-performance liquid chromatography analysis revealed that m
ore than 99% of renal irANF is processed ANF(99-126). This finding sug
gests that most of the irANF measured in kidney extracts likely origin
ates from atrial sources. Left atrial ANF mRNA levels after 1 week of
DOCA-salt treatment was significantly higher than that of control rats
([21.06+/-2.99]x10(-15) mol/mu g total RNA versus [8.59+/-1.26]x10(-1
5) mol/mu g total RNA, P<.05). However, renal ANF mRNA levels in DOCA-
salt rats were significantly decreased compared with those of control
rats ([1.64+/-0.34]x10(-22) mol/mu g total RNA versus [3.96+/-0.61]x10
(-22) mol/mu g total RNA, P<.05). These results indicate that (1) rena
l ANF mRNA can be consistently and specifically demonstrated after rev
erse transcription and PCR amplification; (2) renal and cardiac ANF sy
nthesis are regulated in a tissue-specific, opposite manner during DOC
A-salt treatment; and (3) the finding that renal ANF mRNA is downregul
ated by DOCA-salt treatment together with previous findings suggest th
e need for further investigation into the role of renal ANF mRNA downr
egulation in the pathogenetic mechanism that leads to volume expansion
and hypertension after chronic DOCA-salt treatment.