Lyophilised aqueous extract of Euphorbia hirta L. (Euphorbiaceae) has been evaluated for analgesic, antipyretic and anti-inflammatory properties in mice and rats, in order to complete its activity profile, after the confirmation of the existence of a central depressant activity particularly expressed by a strong sedative effect, associated with anxiolytic effects. This study leads us to the conclusion that this plant extract exerts central analgesic properties. Such a dose-dependent action was obtained against chemical (writhing test) and thermic (hot plate test) stimuli, respectively, from the doses of 20 and 25 mg/kg and it was inhibited by a naloxone pretreatment, a specific morphinic antagonist compound. An antipyretic activity was obtained at the sedative doses of 100 and 400 mg/kg, on the yeast-induced hyperthermia. Finally, significant and dose-dependent anti-inflammatory effects were observed on an acute inflammatory process (carrageenan-induced edema test in rats) from the dose of 100 mg/kg. On the other hand, plant extract remained inactive on chronic processes such as Freund's adjuvant-induced rheumatoid arthritis, after a chronic treatment during fourteen days at the daily dose of 200 or 400 mg/kg; however, if inefficacy was observed on rat backpaws edema and on loss of weight, the aqueous extract reduced the inflammatory hyperalgia.

The dried aqueous extract of Harpagophytum procumbens (Pedaliaceae) and its main iridoid glycoside, harpagoside, have been evaluated for anti-inflammatory and analgesic effects in mice and rats, in order to validate or invalidate the involvement of this compound in such properties. This extract exerted significant and dose-dependent anti-inflammatory and analgesic effects, from the dose 100 mg of dried secondary roots/kg, the first being obtained on an acute inflammatory process (carrageenan-induced edema test in rats) and the second being obtained against a chemical stimulus (writhing test in mice). Harpagoside does not appear to be involved in anti-inflammatory properties, since this iridoid glycoside did not protect against carrageenan inflammatory effects when it was used at 5 and 10 mg/kg; 5 mg corresponding to the quantity contained in 400 mg of dried secondary roots. The main iridoid glycoside of H. procumbens appears to be implicated in the peripheral analgesic properties of this species, but other compounds have to be involved, since the dose of 10 mg/kg exerted a significant protective effect. The absence of the activity of H. procumbens after an acid treatment (0.1 N hydrochloric acid), stomach, suggests the use of a suitable galenic preparation in order to protect the active principles from the action of the acid released in the stomach.

The iridoids of Harpagophytum procumbens and Harpagophytum zeyheri were studied by CLHP. Harpagoside is the main iridoid for both drugs whereas 8-p-coumaroylharpagide is a representative iridoid of Harpagophytum zeyheri only. The ratio harpagoside/8-p-coumaroylharpagide can be used to distinguish chemically both species. For commercial dried aqueous extracts this ratio is intermediate because they are probably prepared from a mixture of H. procumbens and H. zeyheri drugs. The aqueous extracts of both drugs show similar analgesic and anti-inflammatory properties. Harpagophytum procumbens and Harpagophytum zeyheri should be accepted as sources for the drug Harpagophyti radix.

The traditional therapeutic indications for the use of Morinda citrifolia L. (Rubiaceae) have been investigated. The lyophilised aqueous extract of roots of M. citrifolia was evaluated for analgesic and behavioural effects in mice. The extract did not exhibit any toxic effects but did show a significant, dose-related, central analgesic activity in the writhing and hotplate tests; this effect was confirmed by the antagonistic action of naloxone. Furthermore, administration of M. citrifolia extract at high dosages decreased all behavioural parameters in the two compartment test, the light/dark choice situation test, and the staircase test; together with the induced sleeping time, these results are suggestive of sedative properties.

Eschsholzia californica Cham. is a traditional medicinal plant of the Indians used by the rural population of California for its analgesic and sedative properties. Our study on the aqueous extract shows that this plant reduced the behavioural parameters measured in a familiar environment test in mice (novelty preference, locomotion and rearings in two compartments test) at doses above 100 mg/kg and in non-familiar environment tests (staircase test) at doses above 200 mg/kg. This finding validates its traditional sedative properties confirmed by the sleeping induction at doses above 100 mg/kg. Furthermore, when administered at a dose a of 25 mg/kg, E. californica appeared to also have an anxiolytic action since it produced an increase of the number of steps climbed by mice in the staircase test (anticonflict effect) and that of the time spent by animals in the lit box when they were confronted with the light/dark choice situation. Before evaluation of the behavioural effects, it was verified that our aqueous extract did not induce any toxic effect when administered i.p. and p.o.