0944-7113/04/11/04-366 $ 30.00/0 Phytomedicine 11: 366–369, 2004 http://www.elsevier.de/phymed  Introduction Impotence is a serious clinical problem in adult men. The failure of penile erection may be due to impaired relaxation of the smooth muscle of the corpus caver- nosum and several studies indicate that the relaxation is mediated by nitric oxide (NO) released from nonadren- ergic-noncholinergic nerves and from the sinusoidal epithelium (Holmquist et al. 1991; Kim et al. 1991; Rajfer et al. 1992; see also Anderson et al. 1998). Recently we found that extracts of some Argentinian medicinal plants (Baccharis trimera, Haplopappus rigidus, Huperzia saururus, Maytenus ilicifolia, Sat- ureja parvifolia and Senecio eriophyton) possess va- sorelaxing effects (Hnatyszyn et al. 2003). Achyrocline satureioides (Lam.) DC. (Asteraceae), commonly known as “marcela”, is native to the Southeast of South America. The aqueous extract of its aerial parts is used as choleretic, hepatoprotective, antispasmodic and against male impotence (Morton, 1975; Tour- sarkissian,1980). Other investigations have reported antiinflammatory, analgesic, sedative, hepatoprotec- tive, immunostimulating, antiviral, antibacterial and antioxidant properties (Filot da Silva and Langeloh, 1994; Desmarchelier et al. 1998; Kadarian et al. 2002). Phytochemical analyses showed the presence of SHORT COMMUNICATION Flavonoids from Achyrocline satureioides with relaxant effects on the smooth muscle of Guinea pig corpus cavernosum O. Hnatyszyn 1 , V. Moscatelli 1 , R. Rondina 1 , M. Costa 2 , C. Arranz 2 , A. Balaszczuk 2 , J. Coussio 1 and G. Ferraro 1 1 Cátedra de Farmacognosia, IQUIMEFA (UBA-CONICET) 2 Cátedra de Fisiología, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina Summary Ethanol extract of the aerial parts of Achyrocline satureioides (Lam.) DC. (Asteraceae) showed a significant, dose dependent, relaxant effect on the smooth muscle of corpus cavernosum strips, ob- tained from Guinea pig (65.5 ± 4.1% of relaxation at the dose of 25.0 mg/ml). Bioassay guided frac- tionation of this extract furnished two flavonoids, quercetin and quercetin 3-methyl ether, with im- portant vasorelaxing effects on the corpus cavernosum strips (79.8 ± 8.4 and 66.0 ± 4.8% of relax- ation respectively at the dose of 0.075 mg/ml). Two methyl derivatives of quercetin obtained by synthesis, quercetin 3,7,3′,4′-tetramethylether and quercetin 3,5,7,3′,4′-pentamethylether, showed similar relaxant effects at the dose of 0.075 mg/ml (86.4 ± 8.5 and 67.31 ± 1.4% of relaxation re- spectively). The results show that the ethanol extract of A. satureioides and the assayed compounds exhibit significant vasorelaxing properties. Additionally, it is shown that the number of methyl groups in the quercetin nucleus has no significant influence on the effectiveness of these com- pounds. Key words: Achyrocline satureioides, flavonoids, smooth muscle relaxation, corpus cavernosum