Analgesic and anti-inflammatory screening of two Brazilian medicinal plants: a positive and a false-positive result

ABSTRACT

Medical plants used in Brazilian folk medicine to treat pain and inflammation constitute 20 per cent of the current publications on plants in the country. The experimental methods to screen these activities, however, are frequently influenced by previous conditions of the animals and other properties of the tested material unrelated to their putative effects. An example is herein reported on studies carried out with two plants reputed for their anti-inflammatory activities Scoparia dulcis L. collected in Sao Luis, state of Maranhao and Piper marginatum Jacq. collected in Recife, state of Pernambuco. The aerial parts were extracted in hot water, the extracts concentrated and freeze-dried. Previous treatment of rats with either water (0.5 and 1 g/Kg, p.o), decreased the edema produced by carrageenin in the rat paw (40 per cent and 70 per cent), but only the extracts of S. dulcis inhibited the exudate and leukocyte migration induced by carrageenin in the rat pleurisy model (by 60 per cent and 70 per cent, respectively). The ethanolic extract of S. dulcis was more active than the water extract. All extracts reduced the acetic acid induced writhing in mice (by 20 to 60 per cent), the S. dulcis extract being more potent than that of P. marginatum. Both extracts, however, were ineffective in the tail flick test. Intravenous injection of either extract induced hypertension in both anesthetized and unanesthetized rats, but only P. marginatum produced hypertension after oral administration. This effect was blocked after treatment with prazosin (1 mg/Kg). In the isolated rat vas deferens the aqueous and purified extracts induced contractions parallel to those produced by noradrenaline (10(-8) - 10(-4) M) which were blocked by prazosin (10(-7) M). Contractions of electrically paced rat left atria preparations were pontentiated in the presence of either extract (by 30 to 220 per cent), the effect being blocked buy propranolol (2muM). High performance liquid chromatographic analysis of purified hypertensive fractions revealed the presence of both adrenaline and noradrenaline in both extracts. The results indicated that only the S. dulcis extracts presented analgesic/anti-inflammatory effects unrelated to vasoconstriction induced by both catecholamines. The effects obtained upon injection of P. marginatum extracts were unspecific and correlated with the general sympathomimetic effects produced by the extract.