Background: Three types of mixed anesthesia (MMB), consists of medetomidine, midazolam, and butorphanol has been widely used instead of pentobarbital as anesthesia for laboratory animals.

Aims: We evaluated the effect of MMB and pentobarbital on platelet aggregation and considered the validity as anesthesia in hemostatic thrombus formation studies.

Methods: ICR mice, 6-month-old males, were used. For MMB, 4 mg/kg of midazolam, 5 mg/kg of butorphanol, and two different concentrations of medetomidine 0.3 mg/kg or 0.75 mg/kg (0.3MMB and 0.75MMB), and 80 mg/kg of pentobarbital (PENT) were adopted. Platelet-rich plasma (PRP) was collected from each group and was adjusted to 250,000 cells /µL. The aggregation rate induced by collagen or ADP was measured by a light transmission method. We have also examined the pretreatment effect of medetomidine (+MED) or butorphanol (+BUT) on platelets before PENT administration. Furthermore, the α₂ receptor blocker atipamezole was administered in vitro, and the aggregation rate was measured.

Results: The maximum platelet aggregation stimulated with collagen 0.8 µg/mL was 37.2 ± 7.7% in the PENT group and was enhanced to 59.2 ± 5.0 and 86.6 ± 2.9% in the 0.3MMB and 0.75MMB groups, respectively. Aggregation was similarly enhanced in ADP-induced platelet aggregation. In the +MED group, the platelet aggregation was significantly enhanced in comparison with single PENT anesthesia, while not in the +BUT group. Furthermore, the enhancement of platelet aggregation in MMB was suppressed by the addition of atipamezole.

Conclusions: Since the adrenergic α₂ receptor on the platelet membrane is known to send an aggregation-enhancing signal upon stimulation, medetomidine in MMB seems to enhance platelet aggregation via adrenergic α₂ receptor. It would be necessary to pay attention that the aggregation rate is modified by MMB anesthesia, compared with classical pentobarbital.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/effect-of-three-types-of-mixed-anesthesia-mmb-for-platelet-function/