title: Inhibition of FMLP-stimulated neutrophil chemiluminescence by blood platelets increased in the presence of the serotonin-liberating drug chloroquine.
abstract: BACKGROUND
  Previously, we reported that human blood platelets significantly decreased the concentration of reactive oxygen species (chemiluminescence) produced by Ca(2+)-ionophore-stimulated neutrophils and that the reduction was partially mediated by serotonin liberated from platelets during their activation. The aim of the present study was to investigate whether platelet inhibition can occur independently of serotonin liberation and whether it can be pharmacologically enhanced.
  
  
  METHODS
  Chemiluminescence was measured after stimulation of human neutrophils with N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) in the presence of luminophore luminol. Concentration of platelet serotonin was estimated fluorometrically.
  
  
  RESULTS
  Platelets, added to neutrophils in the physiological cell ratio 50:1, decreased neutrophil chemiluminescence by 47%. The inhibition was not accompanied with liberation of platelet serotonin and rose after addition of chloroquine to platelet-neutrophil samples. In the absence of platelets, this drug did not affect neutrophil chemiluminescence. Chloroquine actively liberated serotonin; amine concentrations found in platelet supernatants were sufficient to inhibit neutrophil chemiluminescence.
  
  
  CONCLUSIONS
  The presented results indicate that unstimulated platelets decreased neutrophil chemiluminescence by a serotonin-independent mechanism, yet their inhibitory effect could be enhanced pharmacologically through chloroquine-induced serotonin liberation.
authors.affiliation: Institute of Experimental Pharmacology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04, Bratislava, Slovak Republic. exfavega@savba.sk
authors.forename: Viera
authors.initials: V
authors.lastname: Jancinová
authors.forename: Katarína
authors.initials: K
authors.lastname: Drábiková
authors.forename: Radomír
authors.initials: R
authors.lastname: Nosál'
authors.forename: Margita
authors.initials: M
authors.lastname: Petríková
authors.forename: Milan
authors.initials: M
authors.lastname: Cíz
authors.forename: Antonín
authors.initials: A
authors.lastname: Lojek
authors.forename: Edita
authors.initials: E
authors.lastname: Danihelová
mesh_terms: D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002738:Chloroquine / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008163:Luminescent Measurements; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects* / Q000502:physiology; D017382:Reactive Oxygen Species / Q000097:blood; D016897:Respiratory Burst / Q000187:drug effects*; D012701:Serotonin / Q000378:metabolism*
chemical_list: D017382:Reactive Oxygen Species; D012701:Serotonin; D009240:N-Formylmethionine Leucyl-Phenylalanine; D002738:Chloroquine