Time courses of the anti-anaphylactic and anti-inflammatory effects of dexamethasone in the rat and mouse.

1 The time course of the activity of dexamethasone has been studied in a variety of anaphylactic and inflammatory reactions in the rat and the mouse. 2 The times of peak activity of dexamethasone, expressed as time between oral dosage and induction of response, and the approximate ED50 values (mg/kg) found were: anaphylactic bronchoconstriction in rats, 12-24 h, ED50 1.8; passive cutaneous anaphylaxis in rats, 6 h, ED50 0.04; cutaneous reactions to histamine in rats, 4 h, ED50 0.01; carrageenin-induced paw oedema in rats, 4 h, ED50 0.03; pinnal anaphylaxis in mice, 6 h, ED50 0.82; histamine-induced pinnal reactions in mice, 6 h, ED50 0.05. 3 In rats, the characteristics of the inhibitory effects of dexamethasone indicate a differential activity against anaphylactic and inflammatory reactions and between different types of inflammatory reactions. Possible reasons for these differences are discussed. 4 In mice there was little difference between the inhibition by dexamethasone of cutaneous allergic and histamine-induced reactions. 5 Pinnal anaphylaxis in mice was potentiated by dexamethasone given 1-2 h before challenge.