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-MSH
1 Department of Cell Biology,
We examined the effect of temporary renal ischemia (30 min or 60 min) and reperfusion (1 day or 5 days) on the expression of
renal aquaporins (AQPs) and urinary concentration in rats
with bilateral ischemia-induced acute renal failure (ARF).
Next, we tested whether reducing ischemia/reperfusion (I/R)
injury by treatment with
-melanocyte stimulating hormone (
-MSH)
affects the expression of AQPs and urine output. Rats with ARF showed
significant renal insufficiency, and urinary concentration was markedly
impaired. In rats with mild ischemic injury (30 min), urine output
increased significantly to a maximum at 48 h, and then nearly
normalized within 5 days. Consistent with this, semiquantitative
immunoblotting revealed that kidney AQP1 and AQP2 abundance was
significantly decreased after 24 h to 30 ± 5% and 40 ± 11%
(n = 8) of controls (n = 9), respectively
(P < 0.05). Five days after
ischemia, AQP2 abundance was not significantly decreased and
urine output was normalized. In contrast, severe ischemic injury (60 min) resulted in a marked reduction in urine output at 24 h, despite a
significant decrease in urine osmolality and solute-free water
reabsorption, TcH2O.
AQP1 and AQP2 abundance was markedly decreased to 51 ± 5% and 31 ± 9% (n = 10) of controls
(n = 8) at 24 h
(P < 0.05). After 5 days, the rats
developed gradually severe polyuria and had very low AQP2 and AQP1
levels [11 ± 4% and 6 ± 2%
(n = 5) of controls (n = 8), respectively;
P < 0.05]. A similar reduction
was observed for AQP3. The reduction in AQP expression in the proximal
tubule and inner medullary collecting duct was confirmed by
immunocytochemistry. Next, we found that intravenous
-MSH treatment
of rats with ARF significantly reduced the ischemia-induced
downregulation of renal AQPs and reduced the polyuria. In conclusion,
the I/R injury is associated with markedly reduced expression of the
collecting duct and proximal tubule AQPs, in association with an
impairment of urinary concentration. Moreover,
-MSH treatment
significantly prevented the reduction in expression of AQPs and renal
functional defects. Thus decreased AQP expression is likely to
contribute to the impairment in urinary concentration in the
postischemic period.
acute tubular necrosis;
-melanocyte stimulating hormone; collecting duct; proximal tubule; urinary concentration
mechanism
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