title: Relative contributions of endothelial, inducible, and neuronal NOS to tone in the murine pulmonary circulation.
abstract: Nitric oxide plays an important role in modulating pulmonary vascular tone. All three isoforms of nitric oxide synthase (NOS), neuronal (nNOS, NOS I), inducible (iNOS, NOS II), and endothelial (eNOS, NOS III), are expressed in the lung. Recent reports have suggested an important role for eNOS in the modulation of pulmonary vascular tone chronically; however, the relative contribution of the three isoforms to acute modulation of pulmonary vascular tone is uncertain. We therefore tested the effect of targeted disruption of each isoform on pulmonary vascular reactivity in transgenic mice. Isolated perfused mouse lungs were used to evaluate the effect of selective loss of pulmonary nNOS, iNOS, and eNOS with respect to hypoxic pulmonary vasoconstriction (HPV) and endothelium-dependent and -independent vasodilation. eNOS null mice had augmented HPV (225 +/- 65% control, P < 0.02, mean +/- SE) and absent endothelium-dependent vasodilation, whereas endothelium-independent vasodilation was preserved. HPV was minimally elevated in iNOS null mice and normal in nNOS null mice. Both nNOS and iNOS null mice had normal endothelium-dependent vasodilation. In wild-type lungs, nonselective NOS inhibition doubled HPV, whereas selective iNOS inhibition had no detectable effect. In intact, lightly sedated mice, right ventricular systolic pressure was elevated in eNOS-deficient (42.3 +/- 1.2 mmHg, P < 0.001) and, to a lesser extent, in iNOS-deficient (37.2 +/- 0.8 mmHg, P < 0.001) mice, whereas it was normal in nNOS-deficient mice (30.9 +/- 0.7 mmHg, P = not significant) compared with wild-type controls (31.3 +/- 0.7 mmHg). We conclude that in the normal murine pulmonary circulation 1) nNOS does not modulate tone, 2) eNOS-derived nitric oxide is the principle mediator of endothelium-dependent vasodilation in the pulmonary circulation, and 3) both eNOS and iNOS play a role in modulating basal tone chronically.
authors.affiliation: Cardiovascular Pulmonary Research Laboratory, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA. karen.fagan@uchsc.edu
authors.forename: K A
authors.initials: KA
authors.lastname: Fagan
authors.forename: R C
authors.initials: RC
authors.lastname: Tyler
authors.forename: K
authors.initials: K
authors.lastname: Sato
authors.forename: B W
authors.initials: BW
authors.lastname: Fouty
authors.forename: K G
authors.initials: KG
authors.lastname: Morris
authors.forename: P L
authors.initials: PL
authors.lastname: Huang
authors.forename: I F
authors.initials: IF
authors.lastname: McMurtry
authors.forename: D M
authors.initials: DM
authors.lastname: Rodman
mesh_terms: D000818:Animals; D000860:Hypoxia / Q000503:physiopathology; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout / Q000235:genetics; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000502:physiology*; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D011312:Pressure; D011652:Pulmonary Circulation / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013599:Systole; D014661:Vasoconstriction / Q000502:physiology; D014666:Vasomotor System / Q000502:physiology*; D016278:Ventricular Function, Right
chemical_list: D012333:RNA, Messenger; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496321:Nos1 protein, mouse; C496317:Nos2 protein, mouse; C496315:Nos3 protein, mouse