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1 Departments of Neurology, 2 Anesthesiology and Critical Care Medicine, and 3 Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287; 4 Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390; and 5 Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
Epoxyeicosatrienoic acids are cerebral vasodilators produced in
astrocytes by cytochrome P-450 epoxygenase activity. The P-450 inhibitor miconazole attenuates the increase in
cerebral blood flow (CBF) elicited by glutamate. We evaluated whether
epoxygenase activity is involved in the CBF response to activation of
the N-methyl-D-aspartate (NMDA) receptor subtype
by using two structurally distinct inhibitors, miconazole and
N-methylsulfonyl-6-(2-propargyloxyphenyl) hexanamide
(MS-PPOH), a selective epoxygenase substrate inhibitor. Drugs were
delivered locally through microdialysis probes in striata of
anesthetized rats. Local CBF was measured by hydrogen clearance and
compared with CBF in contralateral striatum receiving vehicle. Microdialysis perfusion of NMDA doubled CBF and increased nitric oxide
(NO) production estimated by recovery of labeled citrulline in the
dialysate during labeled arginine infusion. Perfusion of miconazole or
MS-PPOH blocked the increase in CBF without decreasing citrulline
recovery. Perfusion of
N
-nitro-L-arginine decreased
baseline CBF and inhibited the CBF response to NMDA. Perfusion of
MS-PPOH did not inhibit the CBF response to sodium nitroprusside. We
conclude that both the P-450 epoxygenase and NO synthase
pathways are involved in the local CBF response to NMDA receptor
activation, and that the signaling pathway may be more complex than
simply NO diffusion from neurons to vascular smooth muscle.
arachidonic acid; epoxyeicosatrienoic acid; glia; miconazole; microdialysis; nitric oxide; rat
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