ANTI-ALLERGIC ACTION OF GLUCOCORTICOIDS IN RATS

The effects of three glucocorticoids (steroids: hydrocortisone, prednisolone and dexamethasone) on IgE antibody-mediated immediate hypersensitivity reactions in rats were studied. Forty-eight hr homologous passive cutaneous anaphylaxis (PCA) was inhibited in a dose response manner by the administration of steroids 2 hr prior to challenge. When steroids were administered at various times before challenge, each steroid showed different patterns of time courses for inhibition of homologous PCA. Maximum inhibition was obtained 2 hr after the administration of each steroid. The IgE antibody-mediated histamine release from peritoneal mast cells in vivo was inhibited by the administration of steroids. Time-courses for the inhibitory effects of steroids on histamine release were slightly different from those in PCA. The increase of capillary permeability caused by histamine, serotonin, trypsin or hyaluronidase in the rat skin was not affected by steroids. The inhibitory action of steroids on PCA was not influenced by non-corticoidal steroids (17α-methyltestosterone, androstenedione and progesterone) or arachidonic acid. These results partially explain the inhibitory action of steroids on IgE antibody-mediated immediate hypersensitivity. The inhibition of histamine release would contribute towards the anti-allergic action of steroids but not the antagonistic effect on the mediators. Also the action of glucocorticoids receptor or the inhibition of arachidonic acid production are not vitally important in connection with the antiallergic action of steroids.