Vascular Effects of Ginkgo Biloba Extract (EGb-761) on Isolated Human Umbilical Artery Contraction Responses

Aim: Ginkgo biloba is used in traditional Chinese medicine for the treatment of various illnesses, including asthma, cough, and enuresis. Standardized Ginkgo biloba extract, EGb-761 contains flavonoids and terpenoids, which induce vasorelaxation in animal vessels. Little information is present on the effects of EGb–761 on human umbilical circulation. This in vitro study assesses the vascular effects of EGb-761 on the isolated human umbilical artery and the role of nitric oxide (NO) and prostaglandins in these effects.

Materials and methods: Isolated human umbilical artery strips were suspended in organ baths containing Krebs-Henseleit solution, continuously gassed with 95% O2-5% CO2. After a resting period, the isometric vasoactive changes to the applied agents were recorded. The following experimental procedures were conducted in different groups of strips (n=9); 1) Effect of cumulative EGb-761 (50-500 µg/ml) on the basal tonus of the artery strips. 2) The relaxant effect of cumulative EGb-761 on contraction elicited by 10-6 M 5-HT. 3) Effect of L-NAME incubation on the relaxant effect of cumulative EGb-761 on contraction elicited by 5-HT. 4) Effect of indomethacin incubation on the relaxant effect of cumulative EGb-761 on contraction elicited by 5-HT. 5) Combined effect of L-NAME and indomethacin incubation on the relaxant effect of cumulative EGb-761 on contraction elicited by 5-HT. Mixed effect models were used for Statistical analysis of the data. p<0.05 was considered significant.

Results:

The application of cumulative EGb-761 (50-500 µg/ml) did not alter the basal tone of the artery strips (p>0.05). Cumulative EGb-761 (50-500 µg/ml) generated concentration-dependent relaxation in 5-HT induced contraction (p<0.05). L-NAME significantly reduced the relaxation responses at all concentrations of EGb-761 (50-500 µg/ml) on 5-HT induced contractions (p<0.05). L-NAME completely inhibited relaxation responses of low concentrations (50-100 µg/ml) of EGb-76. Indomethacin significantly inhibited these responses at higher concentrations of EGb-761 (200-500 µg/ml) (p<0.05). L-NAME + indomethacin resulted in significant inhibition of relaxation responses with all concentrations of EGb-761 (50-500 µg/ml) (p<0.05). In addition, the co-administration of L-NAME and indomethacin resulted in a stronger inhibition in these relaxation responses at certain concentrations of EGb-761 than L-NAME and indomethacin alone.

Conclusions: EGb-761 does not affect the basal tone of the human umbilical artery. Cumulative application of EGb-761 in human umbilical artery strips precontracted with 5-HT generates significant concentration-dependent relaxation. NO and prostaglandins are involved in the mechanism of vasodilatation with varying potentials depending on the EGb-761 concentration. Prostaglandins also create synergy with NO in these responses.