Inhibitory effect of norathyriol, a xanthone from Tripterospermum lanceolatum, on cutaneous plasma extravasation

Norathyriol, a xanthone aglycon isolated from Tripterospermum lanceolatum, was demonstrated to reduce the plasma leakage elicited by the passive cutaneous anaphylactic reaction in normal as well as in adrenalectomized mice. Capsaicin pretreatment greatly suppressed the local edema caused by antidromic stimulation of the saphenous nerve. The plasma exudation of neurogenic inflammation was also reduced in mice treated with norathyriol, diphenhydramine and methysergide, but not with indomethacin. Norathyriol, cyproheptadine and diphenhydramine combined with methysergide suppressed the ear edema caused by injection of compound 48/80, bradykinin and substance P into the ear. However, indomethacin did not affect this phlogist-induced edema response. Histamine- and serotonin-induced plasma exudation in ear edema was also reduced by norathyriol. In isolated rat peritoneal mast cell preparations, norathyriol produced a dose-dependent inhibition of histamine and beta-glucuronidase release from mast cells challenged by compound 48/80, bradykinin and substance P. In compound 48/80-pretreated mice, norathyriol at higher concentrations suppressed the bradykinin- and substance P-induced ear edema to a significantly greater extent than diphenhydramine combined with methysergide did. These data indicate that the inhibitory effect of norathyriol on local edema is not due to the release of steroid hormones from the adrenal gland, but is probably partly due to suppression of mast cell degranulation and hence reduce the release of chemical mediators which increase vascular permeability, and partly, at least in higher doses, due to protection of the vasculature from challenge by various mediators.