In vivo production of nitric oxide correlates with n-methyl-d-
aspartate-induced cerebral hyperemia in newborn sheep.
Northington, Frances J., Joseph R. Tobin, Raymond C. Koehler, and
Richard J. Traystman.
The Johns Hopkins Medical Institutions, Departments of Pediatrics
and Anesthesiology/Critical Care Medicine, Baltimore, Maryland
21287
APStracts 2:0045H, 1995.
Stimulation of N-methyl-D-aspartate (NMDA) receptors in brain
increases nitric oxide production in vitro. We tested the hypothesis
that nitric oxide participates in the increase in local cerebral
blood flow (CBF) caused by infusion of NMDA in anesthetized newborn
sheep. We used the combined hydrogen clearance and microdialysis
technique for simultaneous measurement of local CBF, infusion of
drugs, and measurement of interstitial levels of [14C]-L
-citrulline in the parietal cortex. Release of [14C]-L
-citrulline into the dialysate during continuous infusion of
[14C]-L-arginine was used as a marker of nitric oxide
production in vivo. Citrulline recovery and CBF were measured hourly
during a 4 hour infusion of cerebrospinal fluid containing either 1)
no additional drugs, 2) 1 mM NMDA, 3) 1mM NG-nitro-L-arginine methyl
ester (L-NAME, a nitric oxide synthase inhibitor), 4) 1 mM NMDA+1mM
L-NAME, 5) 0.1 mM 2-chloroadenosine (adenosine receptor agonist)and
6) 0.1 mM 2-chloroadenosine +1mM L-NAME. At 240 minutes of perfusion,
CBF (ml_min-1_100g-1); (mean +/- SE) was: control 52+/-3, NMDA 116+/-11, L
-NAME 32+/-5, NMDA+L-NAME 40+/-4, 2-chloroadenosine 201+/-63 and 2
-chloroadenosine+L-NAME 129+/-18. Citrulline recovery (femtomoles/min)
at 240 minutes of perfusion was: control 38+/-12, NMDA 149+/-21, L-NAME
9+/-1, NMDA+L-NAME 39+/-5, 2-chloroadenosine 13+/-5, 2-chloroadenosine + L
-NAME 17+/-1. Infusion of NMDA increased CBF and [14C]-L
-citrulline release and these increases were inhibited by addition of
L-NAME to the dialysate. In contrast, the cerebral vasodilator, 2
-chloroadenosine, with or without L-NAME increased CBF without an
increase in [14C]-L-citrulline release, thereby demonstrating
that the effect of L-NAME to block NMDA-mediated increases in CBF was
specific and not due to generalized vasoparalysis. These results
demonstrate that the local increase in CBF caused by stimulation of
cortical NMDA receptors is dependent on production of nitric oxide.
This study also demonstrates that microdialysate-measured conversion
of [14C]-L-arginine to [14C]-L-citrulline is potentially
useful as a marker of nitric oxide production in vivo.
Received 12 April 1994; accepted in final form 7 February 1995.
APS Manuscript Number H322-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 February 1995.