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-Estradiol corrects hemostasis in uremic rats by limiting
vascular expression of nitric oxide synthases
1 Mario Negri Institute for Pharmacological Research and 2 Division of Nephrology and Dialysis, Azienda Ospedaliera, Ospedali Riuniti di Bergamo, 24125 Bergamo, Italy
Conjugated estrogens
shorten the prolonged bleeding time in uremic patients and are
similarly effective in a rat model of uremia. We have previously
demonstrated that the shortening effect of a conjugated estrogen
mixture or 17
-estradiol on bleeding time was abolished by the nitric
oxide (NO) precursor L-arginine, suggesting that the effect
of these drugs on hemostasis in uremia might be mediated by changes in
the NO synthetic pathway. The present study investigated the
biochemical mechanism(s) by which conjugated estrogens limit the
excessive formation of NO. 17
-estradiol (0.6 mg/kg), given to rats
made uremic by reduction of renal mass, significantly reduced bleeding
time within 24 h and completely normalized plasma concentrations
of the NO metabolites, nitrites and nitrates, and of NO synthase (NOS)
catalytic activity, determined by NADPH-diaphorase staining in the
thoracic aorta. Endothelial NOS (ecNOS) and inducible NOS (iNOS)
immunoperoxidase staining in the endothelium of uremic aortas of
untreated rats was significantly more intense than in control rats,
while in uremic rats receiving 17
-estradiol staining was comparable
to controls. Thus 17
-estradiol corrected the prolonged bleeding time
of uremic rats and fully normalized the formation of NO by reducing the
expression of ecNOS and iNOS in vascular endothelium. These results
provide a possible biochemical explanation of the well-known effect of
estrogens on primary hemostasis in uremia, in experimental animals and humans.
chronic renal failure; conjugated estrogens; bleeding time; endothelium.
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