title: Direct inhibitory mechanisms of halothane on human platelet aggregation.
abstract: BACKGROUND
  Although halothane directly inhibits platelet aggregation, the mechanisms of this effect are still unknown. The current study aimed to clarify the inhibitory mechanisms of halothane on thrombin-induced human platelet aggregation by measuring (1) platelet-surface glycoprotein Ib expression, (2) the concentration of intracellular free Ca2+ ([Ca2+]i) measured simultaneously with aggregation, (3) the concentration of intracellular inositol 1,4,5-triphosphate, and (4) the concentration of intracellular cyclic 3',5'-adenosine monophosphate ([cAMP]i).
  
  
  METHODS
  Washed platelet suspensions, obtained from healthy volunteers, were preincubated with halothane (0-2 mM) for 2 min and then exposed to 0.02 units/ml thrombin for 3 min. The glycoprotein Ib bound to fluorescein-labeled antibody was measured by fluorescence flow cytometry. [Ca2+]i was measured, simultaneously with aggregation, in Fura-2 (Ca2+ indicator)-loaded platelets by use of a fluorometer. Inositol 1,4,5-triphosphate and [cAMP]i were measured by radioimmunoassay.
  
  
  RESULTS
  Halothane had no effect on glycoprotein Ib expression with or without thrombin. Halothane decreased the thrombin stimulated [Ca2+]i transient and inhibited platelet aggregation in a dose-dependent manner, both in the presence and in the absence of external Ca2+. Isoflurane had no apparent effect on either platelet aggregation or [Ca2+]i in the absence of external Ca2+. Halothane inhibited the increase in inositol 1,4,5-triphosphate induced by thrombin. Halothane moderately but significantly increased [cAMP]i, but the adenylate cyclase activator forskolin (which has the same inhibitory ability on aggregation as halothane) increased [cAMP]i to a much greater extent than did halothane.
  
  
  CONCLUSIONS
  Halothane inhibits thrombin-induced human platelet aggregation by decreasing [Ca2+]i without inhibiting agonist-receptor binding; the inhibitory effect of halothane on [Ca2+]i might be mediated by a decrease in inositol 1,4,5 triphosphate and in part by an increase in [cAMP]i.
authors.affiliation: Department of Anesthesiology, Sapporo Medical University School of Medicine, Hokkaido, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kohro
authors.forename: M
authors.initials: M
authors.lastname: Yamakage
mesh_terms: D000328:Adult; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D006221:Halothane / Q000494:pharmacology*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000032:analysis; D007530:Isoflurane / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000032:analysis; D013917:Thrombin / Q000494:pharmacology
chemical_list: D018685:Anesthetics, Inhalation; D010975:Platelet Aggregation Inhibitors; D019038:Platelet Glycoprotein GPIb-IX Complex; D015544:Inositol 1,4,5-Trisphosphate; D007530:Isoflurane; D000242:Cyclic AMP; D013917:Thrombin; D002118:Calcium; D006221:Halothane