HU reduces leukocyte adhesion and extravasation via NO production and a cGMP-dependent pathway. (A) Leukocyte rolling, (B) adhesion and (C) extravasation in TNF-α–treated C57BL6 WT mice after administration of vehicle or HU in the presence or absence of L-NAME, PTIO, or ODQ, n = 4-10 mice per group (*P < .05, **P < .01, ***P < .001, compared with vehicle alone; ##P < .01, ###P < .001 compared with HU alone; ∞∞P < .01, compared with vehicle + L-NAME).