EFFECT OF DEXAMETHASONE ON NEUTROPHIL ACCUMULATION AND EDEMA FORMATION IN RABBIT SKIN - AN INVESTIGATION OF SITE OF ACTION

1 The anti-inflammatory actions of dexamethasone on vascular and leukocyte responses in rabbit skin were investigated. 2 Neutrophil accumulation and oedema formation were simultaneously measured as the local accumulation of i.v. administered In-111-labelled neutrophils and I-125-labelled albumin. Systemically administered dexamethasone (3 mg kg-1) inhibited neutrophil accumulation induced by i.d. zymosan activated plasma (ZAP), N-formyl-methionyl-leucyl-phenylalanine (FMLP) and leukotriene B4 (LTB4) when co-injected with prostaglandin E2 (PGE2). Dexamethasone also inhibited oedema formation elicited by these stimuli and the responses induced by i.d. platelet activating factor (PAF) + PGE2 and bradykinin (BK) + PGE2. 3 Intradermal dexamethasone (2 x 10(-10) mol per site) but not indomethacin ( 10(-8) mol per site) inhibited oedema formation induced by i.d. ZAP + PGE2 and BK + PGE2. This inhibitory effect of dexamethasone was significant only with pretreatment periods of 4 h, shorter pretreatment periods resulting in greatly reduced effects. Intradermal dexamethasone had no effect on neutrophil accumulation induced by ZAP + PGE2. 4 Intradermal dexamethasone (2 x 10(-10)mol per site) had no effect on increase in blood flow induced by PGE2 as measured by Xenon-133 clearance. 5 The accumulation of neutrophils isolated from donor rabbits pretreated with i.v. saline or dexamethasone (3 mg kg-1) was investigated in untreated recipient rabbits. The accumulation of neutrophils, induced by ZAP + PGE2, FMLP + PGE2 and LTB4 + PGE2, from dexamethasone-pretreated donors was significantly smaller than the accumulation of neutrophils from saline-pretreated donors. 6 The results of this study suggest that dexamethasone can have a direct effect on vascular endothelial cells resulting in an inhibition of oedema formation. 7 Neutrophil accumulation can be inhibited by an effect of dexamethasone on the neutrophil itself or on the vascular endothelium. These results indicate that at least part of the inhibitory effect is on the circulating neutrophil induced by dexamethasone or a dexamethasone-induced product.