Mechanisms involved in the antiplatelet activity of midazolam in human platelets.
BACKGROUND
Midazolam is widely used as a sedative and anesthetic induction agent. The aim of this study was to systematically examine the inhibitory mechanisms of midazolam in platelet aggregation.


METHODS
The inhibitory mechanisms of midazolam in platelet aggregation were explored by means of analysis of the platelet glycoprotein IIb-IIIa complex, phosphoinositide breakdown, intracellular Ca+2 mobilization, measurement of membrane fluidity, thromboxane B2 formation, and protein kinase C activity.


RESULTS
In this study, midazolam dose-dependently (6-26 microm) inhibited platelet aggregation in human platelets stimulated by agonists. Midazolam also dose-dependently inhibited phosphoinositide breakdown and intracellular Ca+2 mobilization in human platelets stimulated by collagen. Midazolam (6-26 mum) significantly inhibited thromboxane A2 formation stimulated by collagen in human platelets. Moreover, midazolam (15 and 26 mum) dose-dependently decreased the fluorescence of platelet membranes tagged with diphenylhexatriene. Rapid phosphorylation of a platelet protein of Mr 47,000 (P47), a marker of protein kinase C activation, was triggered by collagen (2 microg/ml). This phosphorylation was markedly inhibited by midazolam (26 microm).


CONCLUSIONS
These results indicate that the antiplatelet activity of midazolam may be involved in the following pathways: the effects of midazolam may initially be caused by induction of conformational changes in platelet membrane, leading to a change in the activity of phospholipase C, and subsequent inhibition of phosphoinositide breakdown and thromboxane A2 formation, thereby leading to inhibition of both intracellular Ca+2 mobilization and phosphorylation of P47 protein.
Sheu
Joen R
JR
Graduate Institute of Medical Sciences and Department of Pharmacology, Taipei Medical University, Taipei, Taiwan. sheujr@tmu.edu.tw
Hsiao
George
G
Luk
Hsiung N
HN
Chen
Yi W
YW
Chen
Ta L
TL
Lee
Lin W
LW
Lin
Chien H
CH
Chou
Duen S
DS
D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003094:Collagen / Q000037:antagonists & inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000097:blood; D008874:Midazolam / Q000494:pharmacology*; D010743:Phospholipids / Q000378:metabolism; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013929:Thromboxane B2 / Q000096:biosynthesis / Q000235:genetics
D005456:Fluorescent Dyes; D006993:Hypnotics and Sedatives; D007295:Inositol Phosphates; D010743:Phospholipids; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D013929:Thromboxane B2; D003094:Collagen; D007770:L-Lactate Dehydrogenase; D011493:Protein Kinase C; D008874:Midazolam; D002118:Calcium; D016257:Fura-2