Pharmacological and Toxicological Activities of the Aqueous Root Extract of AristolochiA Ringens Vahl. (Aristolochiaceae)
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos
Aristolochia ringens Vahl. (Aristolochiaceae) is used traditionally for managing various ailments including gastrointestinal disturbances, rheumatoid arthritis and oedema. This study aims at investigating the pharmacological and toxicological actions of the aqueous root extract of Aristolochia ringens (AR). The toxicological, pharmacological and phytochemical investigations were carried out using standard methods. The extract gave an LC50 of 175 µg/ml in brine shrimp lethality assay, no mortality at 10,000 mg/kg on oral acute exposure, LD50 of 407.38 mg/kg on intraperitoneal acute exposure, and showed relative safety with some adverse reactions on oral subchronic exposure. In the antidiarrhoeal investigation, AR (100-400 mg/kg, p.o.) dose-dependently decreased normal and castor oil-induced intestinal transits significantly (p<0.05-0.001). Its effect was significantly altered by pilocarpine (10 mg/kg, s.c.), phentolamine and propranolol (1 mg/kg, i.p.). The in vivo antidarrhoeal index (ADIin vivo) of AR at 400 mg/kg, 81.79, was comparable to the 86.85 value of morphine (10 mg/kg, s.c.). In the tests to determine its antiinflammatory activity, AR (10-50 mg/kg) significantly decreased rat paw oedema in carrageenan-, egg albumin-, and formaldehyde-induced inflammation tests. At 25-50 mg/kg, AR also significantly reduced the mice ear oedema, with peak effect (84.78% reduction) at 50 mg/kg. In the test to investigate its analgesic action, AR (10-50 mg/kg) significantly reduced the number of writhes induced by acetic acid and acetylcholine. Naloxone (1 mg/kg), glibenclamide (2 mg/kg) but not haloperidol (1 mg/kg), significantly altered the effect of AR, in the acetic acid-induced writhing test. At 10-100 mg/kg, AR dose-dependently reduced cumulative time mice spent paw licking and biting in both phases of formalin-induced pain test significantly. The extract (25-50 mg/kg) and morphine (10 mg/kg) significantly increased response latency to pain induced by tail clip. It also significantly decreased the number of head dips by mice in the hole board test, reduced the number of sectional crossings by mice in the open field test, and significantly increased the duration of sleep in the hexobarbitone-induced sleep test. In the test for the effect of AR on haemodynamic parameters, AR (25 and 50 mg/kg) was found to significantly reduce systolic and diastolic blood pressures in spontaneously hypertensive rats (SHRs). On intravenous acute exposure, the greatest effect was observed at 50 mg/kg with reductions of 53.4±2.2 and 49.2±2.8 mmHg in systolic and diastolic blood pressure respectively. Hexamethonium (20 mg/kg) and atropine (1 mg/kg) inhibited these effects of the extract. Of the fractions of AR tested, the butanol fraction, which was also shown to possess the highest concentrations of phenolics, produced the greatest hypotensive effect. Preliminary phytochemical screening revealed the presence of tannins, alkaloids, saponins, anthraquinones, oils, reducing sugars and phlobatannins in AR. HPLC analysis revealed the presence of 4-hydroxybenzoic acid and quercetin as well as aristolochic acid I in AR. However, no detectable concentrations of aristolochic acid I was found in its butanol and aqueous fractions. GC-MS analysis revealed that AR contains volatile compounds such as 1,2 benzenediol and 1,1,6- trimethyl-1,2-dihydronaphthalene. These findings show that the aqueous root extract of A. ringens possesses antidiarrhoeal, antiinflammatory, analgesic and hypotensive activities.