Vernonia spp. (Asteraceae) are reported in Mexican herbolaria for used in menstrual disorders, hair regeneration, dysentery, and as a coagulant.1) Brazilian folk medicine has shown that the crude extract prepared from leaves of V. condensata prevents stomach and liver disturbances (sic).2) Several of these applications suggest presence of compounds active on smooth muscle. Sesquiterpene lactones, mainly glaucolide-and hirsutinolide-type, have been isolated from Vernonia spp. -sensu latu-.3-6) However, several hirsutinolides might be artifacts formed from glaucolides on exposure to acidic adsorbents during chromatography.7-9) Glaucolides have been reported to elicit molluscicidal, antitumoral, and antimicrobial properties 5,10,11) ; but their effects on smooth muscle have not been investigated previously. Parthenolide, a structurally related sesquiterpene lactone (Fig. 1D) bearing also a germacra-1(10),4-diene-4-epoxide skeleton is known to inhibit smooth muscle contractility likely due to the amethylene g-lactone moiety.12) Therefore, the effects of glaucolides D (Fig. 1A) and E (Fig. 1B) on vascular and uterine smooth muscle contraction were studied. The effect of a hirsutinolide type sesquiterpene lactone (Fig. 1C) lacking both germacrane skeleton and a-methylene g-lactone was also investigated. We have assayed the action of these compounds on smooth muscle pre-contracted with either depolarizing high-KCl solution or an agonist (noradrenaline for aorta and oxytocin for uterus). This model was selected as mean to indicate whether glaucolides D and E are able to relax the contraction dependent on different pathways of calcium influx.
MATERIALS AND METHODSCompounds Glaucolides D (Fig. 1A) and E (Fig. 1B) were isolated from Vernonia liatroides by chromatography and identified by spectroscopic methods as previously described. 3) The hirsutinolide [1R,4S,5R,6S,8S,10R]-8,10,13-triacetoxy-1(4)-epoxy-1,5-dihydroxygermacr-7(11)-en-6(12)-olide ( Fig. 1C) Animals Sprague-Dawley rats, female for uterine experiments and male for aorta experiments, body weight approximately 300 g, were used. Virgin female rats received a subcutaneous injection of estradiol benzoate (40 mg/kg) 24 h prior to the experiment. Animal experiments were performed following the recommendations of the Policies on Animal Experimentation of the Scientific Committee of the Instituto Mexicano del Seguro Social; animals were decapitated, and uterus or descending thoracic aorta were isolated, fat and connective tissue were removed, and tissues were placed in Krebs-Ringer bicarbonate solution.Uterus Experiments Uterine rings (5-7 mm long) were placed in a 5 ml organ bath containing Krebs-Ringer bicarbonate (KRb) solution with the following composition (mM): NaCl, 120; KCl, 4.6; CaCl 2 , 1.5; NaHCO 3 , 20; KH 2 PO 4 , 1.2; MgSO 4 , 1.2, and glucose 11, maintained at 37°C and bubbled with a mixture of 95% O 2 -5% CO 2 (pHϭ7.4). Contractions were recorded isometrically by a force-displacement transducer (Grass, FT03) connected to a Grass polygraph (model 7B)...