The S1P analogue FTY720 and SEW2871 trigger rapid release of platelets. (A) Mice were treated with a single dose of FTY720 (3 mg/kg i.p.) or DMSO (vehicle). Open bars indicate baseline of platelet counts assessed before drug administration; closed bars indicate platelet counts measured 12 h after drug administration. n = 9 mice each group. (B) Representative MP-IVM images of MKs with YFP⁺ PPs from CD41-YFP^ki/+ mice before and 8 h after a single injection of FTY720 (3 mg/kg i.p.) or DMSO (vehicle). Green indicates MKs and PPs; red indicates sinusoids. Arrowheads indicate intravascular PPs. Dashed lines indicate BM sinusoidal vessels. Bars, 20 µm. (C) Fold change of MKs displaying PPF 8 h after a single injection of FTY720 (3 mg/kg i.p.) or DMSO (vehicle) compared with numbers recorded before treatment. n = 120–140 MKs per group. Data are pooled from three independent experiments. (D) Mice were treated with a single dose of SEW2871 (20 mg/kg i.p.) or dimethyl formamide (DMF; vehicle). Open bars indicate baseline of platelet counts assessed before drug administration; closed bars indicate platelet counts measured 12 h after drug administration. n = 3 mice each group. All error bars indicate SEM.