Effects of neutrophils emigration on vascular permeability and anti-inflammatory mechanism of dexamethasone

In rat peritonitis induced by ip carrageenin, depletion of circulating neutrophils (Neu) either by iv nitrogen mustard (1.2, 2.4, 3.6 mg/kg) or by exposure to 60Co (9 Gy) caused the decrease in number of Neu and amount of protein in exudate. However, in histamine-induced peritonitis, although the depletion of circulating Neu by 60Co decreased Neu emigration, the protein exudate was not reduced. Dexamethasone (0.15, 0.5, 1.5 mg/kg) im th before ip carrageenin suppressed both Neu emigration and protein exudate. On the other hand. dexamethasone only inhibited Neu emigration. but had no significant inhibitory effect on protein exudate induced by histamine. The results revealed tbat the increase in vascular permeability induced by carrageenin was dependent on the presence of circulating Neu, so that Neu emigration may be responsible for the exudation of plasma protein through the blood vessel wall. In addition. the primary action of dexamethasone may be an inhibitory action on Neu emigration and then control the vascular permeability.