title: ACh dilates pial arterioles in endothelial and neuronal NOS knockout mice by NO-dependent mechanisms.
abstract: 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 microns). 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 microM) caused atropine-sensitive dose-dependent arteriolar dilation in all three mouse strains. At 10 microM, 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-NNA, 1 mM) superfusion inhibited cortical NOS activity by > 70% and abrogated the response in wild-type mice while blocking the dilation by approximately 50% in eNOS mutant and nNOS mutant mice. Only in the eNOS mutant did tetrodotoxin (TTX) superfusion (1 microM) attenuate ACh-induced dilation (n = 6). The residual dilation after L-NNA in eNOS mutant mice could be blocked completely by TTX-plus L-NNA. 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 the wild-type response except for enhanced dilation to ACh and reduced L-NNA sensitivity, and 3) surprisingly, the response in eNOS mutant mice is partially NOS dependent and attenuated by both TTX and L-NNA. 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.
authors.affiliation: Department of Neurosurgery and Neurology, Massachusetts General Hospital, Charlestown, USA.
authors.forename: W
authors.initials: W
authors.lastname: Meng
authors.forename: J
authors.initials: J
authors.lastname: Ma
authors.forename: C
authors.initials: C
authors.lastname: Ayata
authors.forename: H
authors.initials: H
authors.lastname: Hara
authors.forename: P L
authors.initials: PL
authors.lastname: Huang
authors.forename: M C
authors.initials: MC
authors.lastname: Fishman
authors.forename: M A
authors.initials: MA
authors.lastname: Moskowitz
mesh_terms: D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000201:enzymology / Q000294:innervation; D004730:Endothelium, Vascular / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout / Q000235:genetics*; D009474:Neurons / Q000201:enzymology; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000235:genetics* / Q000378:metabolism; D019335:Nitroarginine / Q000494:pharmacology; D010841:Pia Mater / Q000098:blood supply*; D013779:Tetrodotoxin / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects
chemical_list: D004791:Enzyme Inhibitors; D019335:Nitroarginine; D009569:Nitric Oxide; D013779:Tetrodotoxin; D019001:Nitric Oxide Synthase; D000109:Acetylcholine