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Analgesic Activity and Chemical Constituents of Extracts of two Medicinal Species of URTICA Carla Marrassini, Susana Gorzalczany, Cristina Acevedo, Paula G. López, Graciela E. Ferraro Pharmacognosy and Pharmacology Chairs IQUIMEFA (UBA-CONICET), Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires. Junín 956 (1113), Buenos Aires, Argentina. Email address: gferraro@ffyb.uba.ar Introduction Two South American species were studied, one native, Urtica circularis, and other naturalized, Urtica urens, with similar morphological characteristics, which are locally used in popular medicine for the relief of rheumatic and muscular pain [1][2]. Urtica circularis (Hicken) Sorarú (Urticaceae) is known as ortiga, ortiga crespa, ortiga brava, caá poropí and urtiginha miúda [3]. Urtica urens L. (Urticaceae) is known with the common names ortiga, ortiga negra, caá poropé, rupá chico [3] and dwarf nettle. Materials and Methods The aerial parts were extracted by maceration with 80% ethanol. Writhing test: performed as described by Collier et al. (1968) [4]. Formalin test: performed as described by Hunskaar and Hole (1987) [5]. Total phenolics determination: performed as described by Singleton et al. (1999) [6]. HPLC: performed as described by Filip et al. (2001) [7]. Results / Discussion Writhing test The effect of the U. urens and U. circularis extracts in the writing test was found to have significant antinociceptive activity (only the first significant result is shown): number of writhing: control 29±2; U. urens 30 mg/kg intraperitoneal administration (i.p.) 12±3**; U. urens 250 mg/kg oral administration (p.o) 14±2**; control 31±2; U. circularis 125 mg/kg i.p. 10±4*; U. circularis 500 mg/kg p.o. 16±1*. Indomethacine was used as reference drug (indomethacine 10 mg/kg i.p. 13±3**; **p<0.01, *p<0.05). Formalin test The effect of the U. urens and U. circularis extracts in the formalin test was found to have significant antinociceptive activity (only the first significant result is shown). Licking time, late phase: control 84.5±11.9; U. urens 100 mg/kg i.p. 19.2±8.1**; U. urens 500 mg/kg p.o. 31.4±16.4*; U. urens 100 mg/kg i.p. + naloxone 5 mg/kg i.p. 32.1±12.3*; U. circularis 30 mg/kg 18.2±12.8**; U. circularis 500 mg/kg p.o 9.7±9.7**; U. circularis 500 mg/kg p.o + naloxone19.7±6.7**; Indomethacine and morphine were used as reference drugs (morphine 10 mg/kg subcutaneous administration 0±0**; indomethacine 30 mg/kg i.p. 38.2±5.4*; **p<0.01, *p<0.05) Total phenolics´ determination U. urens: 10.4 GAE/g. and U. circularis: 7.5 GAE/g. HPLC The chromatographic fingerprints are shown in Figures 1 ands 2. Chlorogenic acid (RT: 15.5 min) and a flavonoid glycoside (RT: 24.2 min) are the U. urens´ and U. circularis´ extracts major components respectively. The HPLC profiles could be a useful tool to differentiate between the species. Fig. 1. U. urens HLPC fingerprint Fig. 2. U. circularis HLPC fingerprint Fig. The U. urens and U. circularis´ extracts display a similar behavior showing significant antinociceptive effect in chemically induced mouse pain models. Considering the mechanisms implied in the algesic action produced by acetic acid and formalin in the writhing and formalin tests, respectively, the effect of the extracts might be mediated by the reduction of prostaglandins´ synthesis. Since their activity is significant in the second phase in the Formalin test and as naloxone could not antagonize the effect, it can be concluded that the extracts dont have central activity. In brief, these extracts would act in a similar way to indomethacine, their effect would be unrelated to the activation of the opioid system and the presence of chlorogenic acid or other flavonoid compounds could be responsible for this activity. References [1]Martínez Crovetto R. Plantas Utilizadas en Medicina en el Noroeste de Corrientes, Ministerio de Cultura y Educación, Fund. Miguel Lillo, Tucumán, Argentina. 1981, Miscelánea Nº 69, 37-38. [2]Domínguez JA; Contribuciones a la Materia Médica Argentina, Peuser, Buenos Aires. 1982, 84. [3]Zuloaga FO, Morrone O. Catálogo de Plantas Vasculares de la República Argentina.Missouri Botanical Garden. 1999, 621-622. [4]Collier HDJ, Dinnin LC, Johnson CA, Schneider C. The abdominal response and its suppression by analgesic drugs in the mouse. British Journal of Pharmacology and Chemotherapy 1968, 32 (2), 295-310. [5]Hunskaar S, Hole K. The formalin test in mice: dissociation between inflammatory and non-inflammatory pain. Pain. 1987, 30 (1), 103104. [6]Singleton VL, Orthofer R, Lamuela-Raventós RM. Analysis of total phenols and other oxidation substrates and antioxidants by means of folin-ciocalteu reagent. Methods in Enzymology. 1999, 299, 152-178. [7]Filip R, López P, Giberti G, Coussio J, Ferraro G. Phenolic compounds in seven South American Ilex species. Fitoterapia. 2001, 72, 774778.