Immediate inhibitory effect of methylprednisolone suleptanate (U‐67590A) on antigen‐induced cutaneous and airway anaphylactic responses in guinea‐pigs

1 Inhibitory effects of water‐soluble glucocorticoids administered intravenously were examined on skin and airway reactions caused by antigen challenge or chemical mediators in guinea‐pigs. 2 Methylprednisolone suleptanate (U‐67590A) which is an analogue of methylprednisolone, produced immediate inhibition of 3‐h and 7‐day homologous passive cutaneous anaphylaxis (PCA) reactions, but not of histamine‐ or bradykinin‐induced cutaneous vascular permeability, when administered 10 min before antigen challenge. In contrast, methylprednisolone succinate (MP) or dexamethasone (DXM) administered 10 min before antigen challenge failed to show an immediate inhibitory effect on the PCA or mediator‐induced reactions. When administered 1 to 5 h before antigen challenge, all the steroids used in this study reduced both PCA and mediator‐induced reactions. 3 Pretreatment with cycloheximide almost completely abolished the late inhibition of 3‐h PCA and histamine reactions produced by U‐67590A or MP, but it did not affect the immediate inhibition of 3‐h PCA produced by U‐67590A. 4 U‐67590A also demonstrated immediate inhibitory effects on antigen‐induced bronchoconstriction in guinea‐pigs actively sensitized with ovalbumin even when administered 10 min before antigen challenge, whereas MP and DXM failed to show the immediate inhibitory effect. When administered 3 h before antigen challenge, all the steroids used in this study reduced the response to antigen. 5 The late inhibitory effect of U‐67590A administered 3 h before antigen challenge was almost completely abolished by treatment with cycloheximide or 17α‐methyltestosterone, whereas the immediate inhibition produced by U‐67590A administered 10 min before challenge was not affected by this treatment. 6 U‐67590A administered 10 min or 3h before challenge did not affect the bronchoconstriction induced by histamine or leukotriene D4. 7 Release of histamine from lung fragments of sensitized guinea‐pigs in vitro was inhibited by U‐67590A. 8 The present experiments indicate that U‐67590A demonstrated dual, immediate and late, inhibitory effects. The former are independent of protein synthesis and may be associated with non‐genomic direct action on the mediator‐releasing process without affecting mediator‐induced reactions. The latter share common inhibitory actions with other glucocorticoids which are dependent on protein synthesis through gene expression.