The antinociceptive effect of some Egyptian medicinal plant extracts.

The antinociceptive effect of methanolic extracts (200 and 400 mg kg(-1)) of eight Egyptian medicinal plants was studied using acetic acid-induced writhing and tail-flick test in mice. Oral administration of 400 mg kg(-1) methanolic extracts of Convolvulus fatmensis, Alhagi maurorum, Plantago major seeds, Conyza dioscaridis significantly (P < 0.05) inhibited the nociception to acetic acid-induced writhes with a protection of 85.5-61.3%. Schouwia thebaica, Diplotaxis acris, Plantago major leaves and Mentha microphylla, in the large dose, showed a protection of 50.8-45.8%, which were significantly different as compared to control. The smaller dose of the tested plant extracts did not protect animals from painful acetic acid stimulation with the exception of Alhagi maurorum. In the tail-flick test, methanolic extracts of Mentha microphylla, Conyza dioscaridis, Alhagi maurorum, Plantago major leaves, Diplotaxis acris and Convolvulus fatmensis in a dose of 400 mg kg(-1) produced significant increase in the latency to response of tail to thermal stimulation. Mild or no effect was observed by the small dose with the exception of Diplotaxis acris that had significant antinociceptive effect at the dose of 200 mg kg(-1). The extracts of all tested plants in doses up to 2 g kg(-1) b.wt. did not cause any deaths or major signs of acute toxicity. Phytochemical screening indicated the presence of unsaturated sterols, triterpenes, tannins, flavonoids and carbohydrates and/or glycosides as major constituents.