INHIBITORY EFFECT OF NORATHYRIOL, A XANTHONE FROM TRIPTEROSPERMUM-LANCEOLATUM, ON CUTANEOUS PLASMA EXTRAVASATION

Norathyriol, a xanthone aglycon isolated from Tripterospermum lanceola tum, was demonstrated to reduce the plasma leakage elicited by the pas sive cutaneous anaphylactic reaction in normal as well as in adrenalec tomized mice. Capsaicin pretreatment greatly suppressed the local edem a 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 indom ethacin. 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 s erotonin-induced plasma exudation in ear edema was also reduced by nor athyriol. In isolated rat peritoneal mast cell preparations, norathyri ol produced a dose-dependent inhibition of histamine and beta-glucuron idase release from mast cells challenged by compound 48/80, bradykinin and substance P. In compound 48/80-pretreated mice, norathyriol at hi gher concentrations suppressed the bradykinin- and substance P-induced ear edema to a significantly greater extent than diphenhydramine comb ined with methysergide did. These data indicate that the inhibitory ef fect of norathyriol on local edema is not due to the release of steroi d hormones from the adrenal gland, but is probably partly due to suppr ession of mast cell degranulation and hence reduce the release of chem ical mediators which increase vascular permeability, and partly, at le ast in higher doses, due to protection of the vasculature from challen ge by various mediators.