Relaxation of uterine and aortic smooth muscle by glaucolides D and E from Vernonia liatroides

Vernonia spp. (Asteraceae) are used in herbolaria in Latin America in menstrual and stomach disorders, suggesting smooth muscle relaxing properties of some of their chemical constituents. For pharmacological support for this belief, sesquiterpene lactones glaucolides D and E were assayed on isolated rat smooth muscle. Glaucolide E proved more potent than glaucolide D to relax high KCl- or noradrenaline-induced contractions in aorta and to relax the high KCl-contraction in uterus. Hirsutinolide-type sesquiterpene lactone also was tested but displayed no effect. Relaxation of smooth muscle by structurally related sesquiterpene lactone parthenolide has been attributed mainly to the a-methylene gamma-lactone moiety; because glaucolides D and E lack this functional group, their relaxant properties may rely on other alkylating sites such as C10 of the germacra-1(10),4diene-4-epoxide skeleton.