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Laboratory for Research in Neonatal Physiology, Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
We hypothesize that inhibitory effects
exist between prostanoids and nitric oxide (NO) in their contributions
to cerebral circulation. Piglets (1-4 days old) were divided into
three chronically treated (6-8 days) groups: control piglets,
piglets treated with indomethacin (75 mg/day), and piglets treated with
N
-nitro-L-arginine methyl ester
(L-NAME, 100 mg · kg
1 · day
1). Pial
arterioles dilated in response to hypercapnia similarly among the three
groups (41 ± 4, 40 ± 6, and 45 ± 11%). Cerebrospinal fluid cAMP increased in control piglets, while cGMP increased in
indomethacin-treated piglets. L-NAME, but not
7-nitroindazole, inhibited the response to hypercapnia only in
indomethacin-treated piglets (40 ± 6 vs. 17 ± 5%). Topical
sodium nitroprusside or iloprost restored dilation in response to
hypercapnia. Similar results were obtained when the dilator was
bradykinin. Pial arterioles of control and L-NAME-treated
piglets constricted in response to ACh (
24 ± 3%). However,
those of indomethacin-treated piglets dilated in response to ACh
(15 ± 2%). This dilation was inhibited by L-NAME. NO
synthase activity, but not endothelial NO synthase expression,
increased after chronic indomethacin treatment. These data suggest that
chronic inhibition of cyclooxygenase can increase the contribution of
NO to cerebrovascular circulatory control in piglets.
newborn; cranial window; cerebrovascular circulation; hypercapnia; acetylcholine; bradykinin; permissive
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