Antithrombotic activities of Newbouldia laevis (P. Beauv) seem. ex Bureau leaves

The study evaluated anticoagulant properties of the methanol extract of Newbouldia laevis leaves using blood clotting time, bleeding time and thrombin-induced clotting assay as standard procedures. Oral acute toxicity studies showed that the extract had a high safety margin, up to 2000 mg/kg in Wistar rats. The methanol leaf extract of N. laevis significantly (p<0.05) prolonged blood clotting times from the baseline value of 11.0 ± 0.6 s for the blood sample to 18.0 ± 0.7 s and 32.0 ± 1.0 s at 5 % and 10 % concentrations respectively. The crude extract also exhibited appreciable in vivo and in vitro anticoagulant potency. High doses of the extract were most significant (p<0.01) in inducing rabbit bleeding which became prolonged to 55.8 ± 1.4 s and 73.1 ± 0.8 s at 100 and 200 mg/kg respectively compared to the baseline (18.0 ± 0.2 s) and effects of the reference anticoagulants. Aspirin was found to have produced bleeding intervals of 47.0 ± 0.3 s and 70.1 ± 0.2 s at 1.0 and 2.0 mg/kg while heparin (0.75 and 1.5 mg/kg) induced bleeding times of 41.6 ± 0.8 s and 61.0 ± 1.7 s respectively. The vehicle (distilled water) induced a transient baseline bleeding time of 18.0 ± 0.2 s. However, the leaf extract of N. laevis also potentiated elevation in thrombin-induced clotting time in a dose dependent manner but at a reduced potency compared to heparin. Phytochemical analysis revealed the presence of reducing sugars, alkaloids, tannins, flavonoids, resin, phenols, proteins and acid compounds in the crude extract. The results demonstrated that the methanol leaf extract of N. laevis possesses pharmacologically active anticoagulant principles that could be isolated and evaluated for clinical or physiological purposes.