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Department of Anesthesiology and Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287
Estrogen protects the brain from experimental cerebral
ischemia, likely through both vascular and neuronal cellular
mechanisms. The purpose of this study was to determine whether chronic
estrogen treatment in males and repletion in ovariectomized (Ovx)
females reverses abnormalities in pial arteriolar reactivity during
reperfusion from global forebrain ischemia (4-vessel occlusion,
15 min) and whether the site of protection is vascular endothelium.
Male and Ovx female rats were implanted with either placebo or a
25-µg 17
-estradiol pellet 10 days before ischemia. With
the use of intravital microscopy, pial vessel dilation to ACh (10 µM)
and S-nitroso-N-acetyl-penicillamine (SNAP; 1 µM) and vasoconstriction to serotonin (10 µM) was examined in situ
at 30-60 min of reperfusion. Postischemic changes in
vessel diameter were compared with preischemic values for each
agent. Postischemic response to both ACh and SNAP was lost in
males and Ovx females, but not in estrogen pellet-implanted males and
estrogen-implanted Ovx females, suggesting that estrogen protects both
endothelial and smooth muscle-mediated vasodilation. Ischemia
blunted vessel constriction to serotonin regardless of treatment. These
data demonstrate that estrogen acts as a vasoprotective agent within
the cerebral circulation and can improve microvascular function under
conditions of an acutely evolving ischemic pathology.
cerebral ischemia; microvasculature; pial circulation
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