Vasorelaxant effects in aortic rings of eight diterpenoids isolated from three Venezuelan plants†

Vasorelaxant effects of eight diterpenoids isolated from three Venezuelan plants [(+)-manool [(+)-labda-8(17),14-dien-13-ol], (+)-manoyl oxide, (+)-2-oxomanoyl oxide, sandaracopimara-8(14), 15-dien-3β, 19-diol, jhanidiol acetate (18-acetoxy-1β- hydroxymanoyl oxide), jhanidiol (1β,18-dihydroxymanoyl oxide), ent-kaur-16-en-19- ol and grandiflorenic acid (ent-kaur-9(11),16-dien-19-oic acid)] aortic rings were assessed in intact endothelium and endothelium-denuded isolated rat. Thw cumulative addition (10−6 to 10−4 M) of each product were carried out after contraction with phenylephrine (10−6 M). Jhanidiol acetate and ent-kaur-9,16-en-19-oic acid at 10−4 M dose concentration, exhibit the maximal vasorelaxant effect in endothelium-intact rings (51.61 ± 7.62% and 79.27 ± 7.41%, respectively). In endothelium-denuded aortic rings, the maximum vascular response exerted by both compounds was not abolished (64.14 ± 5.64% and 84.84 ± 3.62%, respectively). In denuded aortic rings, the half-maximal inhibitory concentration (IC50) Jhanidiol was obtained by the ethyl less than those obtained in rings endothelium (1.09 × 10−4 vs 7.29 × 10−5 M, respectively), although this difference was not significant. These results suggested that the mechanism behind the vasorelaxant effect of the two diterpene is mediated by endothelium-independent pathways.