Acetylcholine dilates pial arterioles in endothelial and neuronal
nitric oxide synthase knockout mice by nitric oxide-dependent
mechanisms.
Meng, Wei, Jianya Ma, Cenk Ayata, Hideaki Hara, Paul L. Huang, Mark C.
Fishman, and Michael A. Moskowitz.
Stroke and Neurovascular Regulation Laboratory, Dept. of
Neurosurgery and Neurology; Cardiovascular Research Center*, Dept. of
Medicine; Massachusetts General Hospital, Harvard Medical School,
Charlestown, MA, 02129
APStracts 3:0138H, 1996.
We used mice with deletions in either the endothelial nitric oxide
synthase (eNOS) or neuronal NOS (nNOS) gene to investigate the role
of eNOS and nNOS in acetylcholine (ACh)-induced relaxation of pial
arterioles (20-30 [mu]m). Pial arteriolar diameter was measured by
intravital microscopy through a closed cranial window, and NOS
activity was determined by the conversion of [3H]arginine to
[3H]citrulline in subjacent cortex. ACh superfusion (1, 10 [mu]M)
caused atropine-sensitive dose-dependent arteriolar dilation in all
three mouse strains. At 10 [mu]M, increases of 20+2%, 31+3% and 23+3%
were recorded in wild type (n=25), nNOS mutant (n=15) and eNOS mutant
(n=20) mice, respectively. NG-nitro-L-arginine (L-NA, 1mM)
superfusion inhibited cortical NOS activity by >70% and
abrogated the response in wild type while blocking the dilation by
approximately 50% in eNOS mutant and nNOS mutant mice. Only in the
eNOS mutant did tetrodotoxin (TTX) superfusion (1 [mu]M) attenuate
ACh-induced dilation (n=6). The residual dilation after L-NA in eNOS
mutant mice could be blocked completely by TTX plus L-NA. Our
findings indicate that: 1) ACh dilates pial arterioles of wild type
mice by NOS dependent mechanisms as reported in other species, 2) the
response in nNOS mutant mice resembles wild type except for enhanced
dilation to ACh and reduced L-NA sensitivity, and 3) surprisingly,
the response in eNOS mutant mice is partially NOS-dependent and
attenuated by both TTX and L-NA. Because nNOS is constitutively
expressed in eNOS mutants, these findings coupled with the TTX
results suggest that an nNOS-dependent mechanism may compensate for
the chronic loss of eNOS activity after targeted gene disruption.
Received 6 December 1995; accepted in final form 20 March 1996.
APS Manuscript Number H1133-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96