title: Endothelin-A receptor antagonist-mediated vasodilatation is attenuated by inhibition of nitric oxide synthesis and by endothelin-B receptor blockade.
abstract: BACKGROUND
  The role of endothelin (ET)-1 in maintenance of basal vascular tone has been demonstrated by local and systemic vasodilatation to endothelin receptor antagonists in humans. Although the constrictor effects mediated by the vascular smooth muscle ET(A) receptors are clear, the contribution from endothelial and vascular smooth muscle ET(B) receptors remains to be defined. The present study, in human forearm resistance vessels in vivo, was designed to further investigate the physiological function of ET(A) and ET(B) receptor subtypes in human blood vessels and determine the mechanism underlying the vasodilatation to the ET(A)-selective receptor antagonist BQ-123.
  
  
  RESULTS
  Two studies were performed, each in groups of eight healthy subjects. Brachial artery infusion of BQ-123 caused significant forearm vasodilatation in both studies. This vasodilatation was reduced by 95% (P=.006) with inhibition of the endogenous generation of nitric oxide and by 38% (P<.001) with coinfusion of the ET(B) receptor antagonist BQ-788. In contrast, inhibition of prostanoid generation did not affect the response to BQ-123. Infusion of BQ-788 alone produced a 20% reduction in forearm blood flow (P<.001).
  
  
  CONCLUSIONS
  Selective ET(A) receptor antagonism causes vasodilatation of human forearm resistance vessels in vivo. This response appears to result in major part from an increase in nitric oxide generation. ET(B) receptor antagonism either alone or on a background of ET(A) antagonism causes local vasoconstriction, indicating that ET(B) receptors in blood vessels respond to ET-1 predominantly by causing vasodilatation.
authors.affiliation: Department of Nephrology and Hypertension, University Hospital Utrecht, The Netherlands. t.rabelink@digd.azu.nl
authors.forename: M C
authors.initials: MC
authors.lastname: Verhaar
authors.forename: F E
authors.initials: FE
authors.lastname: Strachan
authors.forename: D E
authors.initials: DE
authors.lastname: Newby
authors.forename: N L
authors.initials: NL
authors.lastname: Cruden
authors.forename: H A
authors.initials: HA
authors.lastname: Koomans
authors.forename: T J
authors.initials: TJ
authors.lastname: Rabelink
authors.forename: D J
authors.initials: DJ
authors.lastname: Webb
mesh_terms: D000328:Adult; D065128:Endothelin Receptor Antagonists; D005260:Female; D005542:Forearm / Q000098:blood supply; D006801:Humans; D008297:Male; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009842:Oligopeptides / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology*; D010880:Piperidines / Q000494:pharmacology; D011453:Prostaglandins / Q000096:biosynthesis; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D012039:Regional Blood Flow / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D065128:Endothelin Receptor Antagonists; D009842:Oligopeptides; D010456:Peptides, Cyclic; D010880:Piperidines; D011453:Prostaglandins; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D014665:Vasodilator Agents; D009569:Nitric Oxide; C086539:BQ 788; D019001:Nitric Oxide Synthase; C072247:cyclo(Trp-Asp-Pro-Val-Leu)