title: Regulation of the endogenous NO pathway by prolonged inhaled NO in rats.
abstract: Nitric oxide (NO) modulates the endogenous NO-cGMP pathway. We determined whether prolonged inhaled NO downregulates the NO-cGMP pathway, which may explain clinically observed rebound pulmonary hypertension. Rats were placed in a normoxic (N; 21% O2) or hypoxic (H; 10% O2) environment with and without inhaled NO (20 parts/million) for 1 or 3 wk. Subsequently, nitric oxide synthase (NOS) and soluble guanylate cyclase (GC) activity and endothelial NOS (eNOS) protein levels were measured. Perfusate cGMP levels and endothelium-dependent and -independent vasodilation were determined in isolated lungs. eNOS protein levels and NOS activity were not altered by inhaled NO in N or H rats. GC activity was decreased by 60 +/- 10 and 55 +/- 11% in N and H rats, respectively, after 1 wk of inhaled NO but was not affected after 3 wk. Inhaled NO had no effect on perfusate cGMP in N lungs. Inhaled NO attenuated the increase in cGMP levels caused by 3 wk of H by 57 +/- 11%, but there was no rebound in cGMP after 24 h of recovery. Endothelium-dependent vasodilation was not altered, and endothelium-independent vasodilation was not altered (N) or slightly increased (H, 10 +/- 3%) by prolonged inhaled NO. In conclusion, inhaled NO did not alter the endogenous NO-cGMP pathway as determined by eNOS protein levels, NOS activity, or endothelium-dependent vasodilation under N and H conditions. GC activity was decreased after 1 wk; however, GC activity was not altered by 3 wk of inhaled NO and endothelium-independent vasodilation was not decreased.
authors.affiliation: Department of Biomedical Engineering, University of Virginia Health System, Charlottesville, Virginia 22906-0010, USA.
authors.forename: D U
authors.initials: DU
authors.lastname: Frank
authors.forename: D J
authors.initials: DJ
authors.lastname: Horstman
authors.forename: G N
authors.initials: GN
authors.lastname: Morris
authors.forename: R A
authors.initials: RA
authors.lastname: Johns
authors.forename: G F
authors.initials: GF
authors.lastname: Rich
mesh_terms: D000280:Administration, Inhalation; D000818:Animals; D015153:Blotting, Western; D002849:Chromatography, Gas; D006152:Cyclic GMP / Q000502:physiology; D004730:Endothelium, Vascular / Q000502:physiology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000860:Hypoxia / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D009569:Nitric Oxide / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000235:genetics; D052250:Nitric Oxide Synthase Type III; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
chemical_list: D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D006162:Guanylate Cyclase; D006152:Cyclic GMP