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Atrial natriuretic peptide (ANP), mainly store in atrial cells.
In recent years, many organs are found to have performs of
ANP gene or staining of ANP prohormone. In
1988, Schultz-knappe found that urodilatin could
be separated from human urine but not from plasma, so
that urodilatin is recognized to be synthesized by the kidney.
Several researcheres found in sucession by means of
immunocytochemistry and reverse transcription- polymerase chain
reaction (RT-PCR) with Southern blot hybridization that there
are similarities of ANP prohormone and a little ANP
mRNA existing in the kidney. In 1996, our
laboratory found that ANP mRNA performs of diabetes
rats, DOCA-salt rats and water-deprived rats were
increased. In order to prove it further that the constitution of
ANP in a kidney under physiopathology was indeed increasing.
Male Wistar rats were divided into two
experiments. the effect of 4-day water deprivation
on ANP synthesis was studied on 11 normal rats (WD)
with 12 normal rats serving as the normal control group (NC). In
Experiment 1, using reverse-phase high performance liquid
chromatography ( RP-HPLC)followed by radioimmunoassay, defined
immunoreactive ANP (irANP) molecular form with concentration in
renal, and plasma of NC and WD groups. In Experiment 2, using
RT- PCR followed by Southern blot hybridization,
detected renal ANP mRNA level.
After water deprivation for four days, plasma sodium
concentration, osmolality, plasma angiotensin II and
vasopressin levels were increased in WD group but plasma ANP
decreased. We also found that were the performs
of ANP mRNA markedly enhanced in renal outer and inner
medullary in WD group as compared to NC group, respectively.
The analysis of RP-HPLC showed that the molecular types of irANP
in normal rat kidneys were 97.1% of -ANP-(1-28) and
2.9% of proANP while those in water-deprived rat
kidneys were 48.5% of -ANP-(1-28) and 51.5% of proANP.
The same analysis was applied to the plasma of both
normal and water-deprived rats and demonstrated that the irANP
in both groups was -ANP-(1-28). This implied that the
proANP of water- deprived rat kidneys is not trapped
from blood circulation. According to the above result, the
expression of ANP mRNA in medulla and the content of
proANP in total kidneys were increased simultaneously in water-
deprived rats compared with normal ones. This shows that the ANP
synthesis in kidneys does increase in a volume-deprived
condition. The renal ANP synthesis increased whereas
plasma ANP markedly decreased. The observation shows
that ANP in the kidney and heart should be
regulated in two different systems, could have different
mechanisms and physiological function. In the water-
deprived rat, the renal synthesis of ANP was increased in
association with the simultaneous increase of plasma
AgII, AVP, sodium concentration, and osmolality. The increased
renal ANP, thus, may counteract the detrimental effect on renal
function from those vasoconstrictors in the volume
depletion state.
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