title: Platelet aggregation may not be a prerequisite for collagen-stimulated platelet generation of nitric oxide.
abstract: By determining the sum of the supernatant concentrations of nitrite and nitrate the stimulated generation of nitric oxide (NO) by human washed platelets induced by a range of fibrillar collagen concentrations (0.0156-25 microg ml(-1)) was investigated. Platelet serotonin (5-hydroxytryptamine, 5-HT) efflux and platelet aggregation were also measured. Under resting conditions (0 microg ml(-1) collagen) platelet NO release was equivalent to 1.06+/-0.17 nmol per 10(8) platelets. Maximal NO release, equivalent to 2.1+/-0. 37 nmol per 10(8) platelets, was observed with only 0.0625 microg ml(-1) collagen (P<0.02, stimulated vs. resting release), higher collagen concentrations producing no further increases in platelet NO output. By contrast, maximal platelet aggregation and 5-HT efflux did not occur until collagen concentrations of 2.5 microg ml(-1) and 10-25 microg ml-1), respectively, had been achieved. L-NAME (1 mmol l(-1)) and L-NMMA (1 mmol l(-1)) inhibited stimulated platelet NO generation by 78+/-6% and 72%, respectively. Contrasting with fibrillar collagen, fibrillar beta-amyloid protein had no effect on platelet NO generation, or on 5-HT efflux or aggregation. These data perhaps indicate that NO generation by human platelets is stimulated by concentrations of fibrillar collagen insufficient to elicit an aggregatory response. Such a mechanism could operate in vivo to inhibit platelet aggregation which might otherwise be induced by low concentrations of circulating agonists.
authors.affiliation: Department of Medicine, Royal Free and University College Medical School, Sir Jules Thorn Institute, Middlesex Hospital, Mortimer Street, London, UK. christopher.smith@ucl.ac.uk
authors.forename: C C
authors.initials: CC
authors.lastname: Smith
authors.forename: L
authors.initials: L
authors.lastname: Stanyer
authors.forename: M B
authors.initials: MB
authors.lastname: Cooper
authors.forename: D J
authors.initials: DJ
authors.lastname: Betteridge
mesh_terms: D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D003094:Collagen / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects; D012680:Sensitivity and Specificity; D012701:Serotonin / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D012701:Serotonin; D003094:Collagen; D019331:NG-Nitroarginine Methyl Ester