Endothelium-dependent relaxations of rabbit isolated aorta produced by carbachol and by Ginkgo biloba extract

Spirally-cut strips of rabbit aorta were used to examine the relaxations produced by carbachol and extract of Ginkgo biloba (Gb) under isometric conditions. After precontracting the strips with phenylephrine (10(-7) M), carbachol produced a dose-related relaxation (PD2 congruent to 6.2 +/- 0.1) and this effect was antagonized competitively by atropine (PA2 congruent to 9.4 +/- 0.1). Gb (0.2 or 0.3 mg/ml) also relaxed the strips. Removal of the endothelium or a 30-min pre-treatment of the strips with a substance that has lipoxygenase-inhibitor activity (nordihydroguaiaretic acid, NDGA, 10(-5) M) abolished the relaxant effect of carbachol and partially blocked the relaxant effect of Gb. Thus, at least part of the relaxant effect of Gb is mediated by a factor(s) (e.g., EDRF) that is released from endothelial cells.