Summary

Background and objective: The expression of P-selectin on the surface of platelets and platelet–leucocyte conjugate formation are considered to be an indicator of platelet activation in thrombotic and inflammatory disease. Midazolam is a widely used sedative and anaesthetic induction agent. It may inhibit platelet aggregation and suppress interleukin-6 and -8 response in human leucocytes, but any effect on the adhesion of activated platelets to leucocytes remains obscure. We have examined the influence of midazolam on adenosine diphosphate (ADP)-induced platelet surface P-selectin expression and platelet–leucocyte aggregation in whole blood.

Methods: Human whole blood was stimulated with 2 × 10−5M ADP in the presence of midazolam (3 × 10−4 to 3 × 10−6M). Samples were stained with a fluorochrome-conjugated CD62P and CD41a antibody for detecting human platelet P-selectin antigens. The leucocyte subpopulations were separately gated and platelet–leucocyte aggregates were defined as cells found positive for CD45 and CD62P. All samples were analysed and were electronically separated into specific cell types (platelets, neutrophils, monocytes and lymphocytes) according to their typical forward/side scattering by flow cytometry.

Results: Midazolam significantly inhibited ADP-induced platelet P-selectin expression and attenuated platelet–leucocyte aggregation (mainly in neutrophils and monocytes) in a dose-dependent manner with a maximum inhibitory effect at 3 × 10−4M (P < 0.01).

Conclusions: This study demonstrated that midazolam decreases the ADP-induced expression of platelet surface P-selectin and platelet–leucocyte aggregation.