Effects of cannabinoids on mobilization of hematopoietic stem and progenitor cells in C57BL/6J mice. (A) Effects of intraperitoneal injections of cannabinoid agonists (10 mg/kg once daily for 4 days) on the number of circulating peripheral blood-HSPCs in WT mice. Twenty-four hours after the last injection, peripheral blood was collected, and an in vitro colony formation assay was done. The y-axis indicates the number of colonies per 1 × 10⁵ blood cells. Data are mean ± SD (n = 18). *P < .05. **P < .01. (B) Effect of CP55940 on mobilization of wt and Cnr2^−/− HSPC. *P < .05 vs control; **P < .05 vs WT. Data are mean ± SD (n = 18). (C) WT mice received intraperitoneal injections of G-CSF twice daily for 4 consecutive days. Cannabinoid antagonists were injected intraperitoneally into mice 30 minutes before each G-CSF injection. The antagonist AM630 (for CB₂) was applied at a concentration of 5 mg/kg. Frequency of PB-HSPCs was assessed as described above. Data are mean ± SD (n = 12). *P < .01 vs control. **P < .05 vs G-CSF alone. (D) Effects of Cnr2^−/− knockout on the G-CSF-induced mobilization of PB-HSPCs. WT and Cnr2^−/− mice received intraperitoneal injections of G-CSF and cannabinoid antagonist as indicated. Data are mean ± SD (n = 12). **P < .05 vs G-CSF in WT mice.