title: Heparin-induced vasodilation in human hand veins.
abstract: OBJECTIVE
  To investigate whether heparin produces vasodilation in human veins and to explore the underlying mechanisms.
  
  
  METHODS
  Eleven healthy volunteers were studied with the dorsal hand vein compliance technique. Dose-response curves to heparin and enoxaparin were generated. Dose-response curves to heparin were also constructed before and after heparin was infused with the nitric oxide synthase inhibitor N(G)-monomethyl-l-arginine (L-NMMA) or combined histamine H1- and H2-receptor blockade.
  
  
  RESULTS
  Heparin but not enoxaparin caused significant dose-dependent relaxation with an average apparent maximal response (at an infusion rate of 20 IU/min) of 47% +/- 23%. L-NMMA attenuated heparin-induced relaxation (P < .001). The combination of H1-and H2-receptor antagonists attenuated heparin-induced relaxation to a lesser extent (P < .05). Heparin-induced relaxation decreased by 52%, 73%, and 35% in the presence of L-NMMA, indomethacin (INN, indometacin) plus L-NMMA, and combined H1- and H2-receptor blockade, respectively.
  
  
  CONCLUSIONS
  Heparin is an endothelium-dependent venodilator in humans. The mechanism of heparin-induced relaxation involves an increased availability of nitric oxide, possibly partially related to local release of histamine.
authors.affiliation: Department of Medicine, Stanford University School of Medicine, Calif, USA.
authors.forename: O
authors.initials: O
authors.lastname: Tangphao
authors.forename: S
authors.initials: S
authors.lastname: Chalon
authors.forename: H J
authors.initials: HJ
authors.lastname: Moreno
authors.forename: A K
authors.initials: AK
authors.lastname: Abiose
authors.forename: T F
authors.initials: TF
authors.lastname: Blaschke
authors.forename: B B
authors.initials: BB
authors.lastname: Hoffman
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D017984:Enoxaparin / Q000494:pharmacology; D005260:Female; D006225:Hand / Q000098:blood supply*; D006493:Heparin / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D008297:Male; D012016:Reference Values; D014664:Vasodilation / Q000187:drug effects*; D014680:Veins / Q000187:drug effects; D014838:Volunteers
chemical_list: D000925:Anticoagulants; D017984:Enoxaparin; D006493:Heparin