title: The flavonoid luteolin induces nitric oxide production and arterial relaxation.
abstract: OBJECTIVE
  Luteolin, a flavone present in many foods and medicinal plants, may have beneficial effects on various human chronic diseases. In the present study, we investigated the hypothesis that luteolin can directly act on vascular endothelial cells (ECs), leading to nitric oxide (NO) production and subsequent vascular relaxation.
  
  
  METHODS
  Rat aortic rings were mounted in organ bath. Luteolin was added cumulatively, and vessel relaxation of rat aortic rings precontracted with phenylephrine (PE) or potassium was recorded. Endothelial nitric oxide synthase (eNOS) phosphorylation at Ser1177 and NO production from aortic rings and primary human aortic endothelial cells (HAECs) exposed to luteolin were measured by using Western blot and fluorometric assay, respectively.
  
  
  RESULTS
  Luteolin dose-dependently (10-100 μmol/L) elicited relaxation of PE- or potassium-contracted aortic rings. The vasorelaxation effect of luteolin was attenuated by the eNOS inhibitor, N-nitro-L-arginine methyl ester, suggesting that this luteolin action is at least partially mediated by activating eNOS activity. We further found that luteolin dose-dependently (10-100 μmol/L) increased eNOS phosphorylation at Ser1177 (up to 1.9-fold) in isolated rat rings. Consistently, exposure of HAECs to luteolin also increased eNOS phosphorylation and NO production.
  
  
  CONCLUSIONS
  Luteolin may be a vascular protective agent by directly acting on vascular ECs to stimulate NO-dependent vascular dilatation.
authors.affiliation: Department of Human Nutrition, Foods and Exercise, College of Agriculture and Life Sciences, Virginia Tech, Blacksburg, VA, 24061, USA.
authors.forename: Hongwei
authors.initials: H
authors.lastname: Si
authors.forename: Richard P
authors.initials: RP
authors.lastname: Wyeth
authors.forename: Dongmin
authors.initials: D
authors.lastname: Liu
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D001120:Arginine / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D047311:Luteolin / Q000494:pharmacology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D010656:Phenylephrine; C026512:arginine methyl ester; D009569:Nitric Oxide; D001120:Arginine; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D047311:Luteolin