EFFECTS OF GINKGO-BILOBA EXTRACT (EGB-761) ON ARTERIOLAR SPASM IN A RAT CREMASTER MUSCLE PREPARATION

The effects of an extract of Ginkgo biloba (EGb 761) on arteriolar spa sm were confirmed using a preparation of rat cremaster muscle. When va sospasm was induced by rat serum, arteriolar constriction reached 25-3 0% of the initial diameter after 10 min. Intravenous injection of EGb 761 (30 mg/kg) 5 min The effects of an extract of Ginkgo biloba (EGb 7 61) on arteriolar spasm were confirmed using a preparation of rat crem aster muscle. When vasospasm was after inducing spasm inhibited about 80 % of this serum-induced vasoconstriction. As previous studies have shown that EGb 761 has an antiaggregatory effect on platelets, thrombi n, serotonin (platelet-derived compounds that are present in the serum ) and a thromboxane analogue (U46619) were also used to induce vasospa sm. Administration of EGb 761 (30 mg/kg) 5 min after exposure of the p reparation to serotonin (10(-3) M) or 10 min after exposure to thrombi n (20 units) did not affect vasospasm induced by these agents. In cont rast, treatment with this same dose of EGb 761 5 min after exposure of the preparation to U46619 (10(-4) M) abolished the arteriolar constri ction induced by this agent in 15 min. The thromboxane/prostaglandin H -2 receptor antagonist SQ29548 antagonized serum-induced vasospasm, in dicating an involvement of thromboxane. Other experiments indicated th at the effects of EGb 761 of counteracting vasospasm may be mediated i n part by ginkgolide B, a triterpene constituent of the extract that i s an antagonist of platelet-activating factor and in part by an 'NO-li ke' action of its proanthocyanidin constituents. Taken together, these results have revealed that EGb 761 treatment can antagonize the vasoc onstrictor effect of thromboxane on arterioles. As thromboxane is impl icated in many cardiovascular disorders, this property of EGb 761 may explain some of its beneficial clinical effects in such pathologies.