title: Benzodiazepines inhibit human platelet activation: comparison of the mechanism of antiplatelet actions of flurazepam and diazepam.
abstract: These studies were undertaken to examine the effects and the mechanism of action of flurazepam and diazepam on human platelet activation. One minute preincubation with flurazepam (3-300 microM) or diazepam (3-300 microM) inhibited platelet aggregation, serotonin secretion and prostaglandin synthesis induced by ADP (1-5 microM), epinephrine (1-5 microM), and arachidonic acid (600-1000 microM). However, 357% higher concentration of diazepam (265 microM) as compared to flurazepam (58 microM), was required to inhibit arachidonic acid induced production of malondialdehyde (MDA) by 50%. In addition, flurazepam and not diazepam inhibited the release of arachidonic acid from platelet phospholipids in a concentration dependent manner. In other experiments flurazepam but not diazepam also blocked aggregation and secretion induced by U46619 (2 microM), a stable analog of prostaglandin H2. Platelet aggregation and serotonin secretion induced by collagen (40-300 micrograms/ml) was inhibited by flurazepam with an IC-50 of 153 microM and 136 microM respectively, whereas higher than 300 microM diazepam was required to inhibit collagen-induced aggregation and secretion by 50%. Flurazepam and diazepam both exhibited their most potent antiplatelet effects against phospholipase C-induced aggregation which is mediated by prostaglandin-independent mechanisms. Only 15 microM and 11 microM flurazepam and 31 microM and 27 microM diazepam were needed to inhibit PLC-induced aggregation and secretion of serotonin by 50% respectively. Effects of these benzodiazepines on platelet cyclic AMP and cyclic GMP were also examined. Neither flurazepam nor diazepam caused any significant change in cyclic AMP or cyclic GMP levels in platelets. These findings suggest that: (a) flurazepam, as compared to diazepam, is 106% - 357% more effective in inhibiting platelet aggregation and serotonin secretion induced by arachidonic acid, collagen and phospholipase C; (b) flurazepam inhibits platelet activation by inhibiting the release of arachidonic acid, its conversion into prostaglandins and by blocking the action of prostaglandins on platelets; (c) diazepam does not inhibit thrombin-induced release of arachidonic acid, conversion of exogenously added arachidonic acid into MDA, or the action of prostaglandins; (d) both flurazepam and diazepam inhibit PLC-mediated activation of platelets; and (e) neither diazepam nor flurazepam achieve their antiplatelet actions by affecting platelet cyclic nucleotide levels.
authors.forename: K
authors.initials: K
authors.lastname: Romstedt
authors.lastname: Huzoor-Akbar
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology; D001570:Benzodiazepinones / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism*; D003094:Collagen / Q000494:pharmacology; D000242:Cyclic AMP / Q000097:blood; D006152:Cyclic GMP / Q000097:blood; D003975:Diazepam / Q000494:pharmacology*; D004837:Epinephrine / Q000494:pharmacology; D005442:Flumazenil; D005479:Flurazepam / Q000494:pharmacology*; D006801:Humans; D008315:Malondialdehyde / Q000097:blood; D010974:Platelet Aggregation / Q000187:drug effects*; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D012701:Serotonin / Q000097:blood; D013917:Thrombin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D001095:Arachidonic Acids; D001570:Benzodiazepinones; D011450:Prostaglandin Endoperoxides, Synthetic; D016718:Arachidonic Acid; D012701:Serotonin; D005442:Flumazenil; D008315:Malondialdehyde; D000244:Adenosine Diphosphate; D003094:Collagen; D000242:Cyclic AMP; D010738:Type C Phospholipases; D013917:Thrombin; D006152:Cyclic GMP; D005479:Flurazepam; D003975:Diazepam; D004837:Epinephrine