The contribution of cannabinoid receptors to the effects of URB597 on leukocyte trafficking in the inflamed knee. (A) Number of rolling leukocytes per minute 20 min after administration of URB597 (0.3 mg/kg) to acutely inflamed knees. Local application of the drug significantly decreased the number of rolling leukocytes and this effect was blocked by local pretreatment with the CB1 receptor antagonist AM251 (0.2 mg/kg) and the CB2 receptor antagonist AM630 (0.2 mg/kg). (B) Number of adherent leukocytes per 50 μm of vessel 20 min after URB597 administration. Leukocyte adhesion was significantly reduced by URB597 administration and this effect was not blocked by either cannabinoid receptor antagonist. Data are means ± SEM. *P <0.05, one-way ANOVA with Bonferroni's post hoc test vs. URB597 (0.3 mg/kg); n =6 to 11. ANOVA, analysis of variance; SEM, standard error of the mean.