Dexamethasone inhibits leukocyte emigration in rat mesenteric post‐capillary venules: an intravital microscopy study

The effect of subcutaneous administration of dexamethasone (DEX) on interleukin‐lβ (IL‐lβ, 20 ng i.p., – 2 h) and platelet‐activating factor (PAF, 100 nM in superfusion) ‐induced leukocyte interaction with the endothelium of rat mesenteric post‐capillary venules was studied. DEX produced a dose‐dependent inhibition of IL‐lβ‐induced leukocyte extravasation in the rat mesenteric vascular bed, with a calculated ED 50 of 40 μg/kg and a maximal effect of 80–100% inhibition at 0.1 mg/kg. IL‐lβ‐induced cell adhesion to post‐capillary venules was only partially inhibited by the steroid, with a calculated ED 50 of 480 μg/kg and a maximal effect of 40–60% inhibition. Furthermore, the steroid inhibited leukocyte emigration, but not adhesion, caused by superfusion of the mesenteric vascular bed with PAF. A doubling of leukocyte emigration time (from 226 to 552 s) was observed after treatment of rats with DEX. Administration for 5 days of a dose of 10 μg/kg DEX (which was inactive when given as a single injection) resulted again in a selective inhibition of IL‐lβ‐induced leukocyte emigration, without effect on cell adhesion. These data demonstrate a preferential susceptibility of the leukocyte emigration process to the inhibitory action of DEX. J. Leukoc. Biol. 62: 301–308; 1997.