Steroid inhibition of oedema formation in the rat skin.

1. A model has been developed to compare the inhibitory effects of the topical steroid, betamethasone-17-valerate, to those of systemically administered betamethasone upon oedema responses induced by 5-hydroxytryptamine (5-HT), platelet activating factor (PAF) and zymosan-activated serum (ZAS) +/- prostaglandin E1 (PGE1), measured in the rat skin by use of 125I-labelled human serum albumin. 2. Systemic betamethasone had a selective, time- and dose-dependent inhibitory effect upon oedema treatment, with 1 mg kg-1 and a 3 h pretreatment having the greatest effect of the doses and times employed. 3. Topical betamethasone inhibited the oedema responses to all of the stimuli showing no apparent selectivity. 4. Topical betamethasone inhibits inflammatory stimuli in a different manner from systemic betamethasone. The broad spectrum of inhibition suggests that topical betamethasone acts by affecting a fundamental feature of the inflammatory response common to all of the stimuli.