SOME CARDIOVASCULAR ACTIVITIES OF THE AQUEOUS LEAF EXTRACT OF CROTON ZAMBESICUS LINN (EUPHORBIACEAE) IN LABORATORY ANIMALS
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Abstract
Croton zambesicus Linn (Euphorbiaceae) is a highly valued medicinal plant in Nigeria and West African sub-region. It is used by traditional medicine practitioners in the treatment of various ailments including hypertension. This study aims to determine some cardiovascular activities of the aqueous leaf extract and subfractions of Croton zambesicus in laboratory animals. The leaves of Croton zambesicus were extracted with water and subsequently subjected to column chromatography to obtain named sub-fractions A preliminary phytochemical screening of the aqueous extract and pooled column subfractions was carried out. The median lethal dose (LD50) of the aqueous extract was determined in mice and rats and the hypotensive activity was assessed in anaesthetized normotensive cats. The diuretic activity was determined in rats and the effect of the extract on uric acid concentration in fructose fed rats was also evaluated. The effect of the extract on isolated right atrium of the guinea pig and isolated perfused heart of the rabbit were determined. The smooth muscle relaxant activity was determined in isolated rabbit ileum while inhibition of angiotensin II, acetylcholine, calcium chloride and potassium chloride-induced contraction of the rat ileum were used to determine it‟s mechanism. The extract was screened for angiotensin converting enzyme inhibitory activity using bradykinin-induced contraction of rat ileum and spectrophotometry. The subfractions were screened for inhibitory effect on acetylcholine and angiotensin II-induced contraction of rat ileum and subfractions with inhibitory effect were further screened for hypotensive activity in anaesthetized normotensive cats. Preliminary phytochemical analysis of the aqueous leaf extract and subfractions revealed the presence of flavonoids, tannins, saponins, triterpenes and alkaloids. The oral median lethal dose (LD50) was greater than 5,000 mg/kg in both rats and mice. The extract (20 and 40 mg/kg i.v.) produced a significant (P<0.001) reduction in the blood pressure of anaesthetized normotensive cat. At 10 mg/kg the extract had significant (P<0.01) diuretic activity in rats vi comparable to that of hydrochlorothiazide (10 mg/kg). The extract (2.5 mg/ml) produced a significant (P<0.05) reduction in the tone and rate of contraction of isolated right atrium of the guinea pig. In addition, the extract (6.4 mg/ml) inhibited isoprenaline (10 nM)-induced contraction of the isolated rabbit heart. The aqueous extract (3.20 and 6.40 mg/ml) produced a significant (P<0.001) reduction in spontaneous contraction of the rabbit ileum. Furthermore, the extract (0.32-6.40 mg/ml) produced a significant (P<0.001) concentrationdependent inhibition of angiotensin II-induced contraction of the rat ileum with an IC50 of 0.50±0.03 mg/ml. Conversely the aqueous extract (0.32 and 0.64 mg/ml) had no significant inhibitory effect on acetylcholine and calcium chloride-induced contractions of the rat ileum. A ten times higher concentration of the extract (3.20 and 6.40 mg/ml) significantly (P<0.001) inhibited acetylcholine and calcium chloride-induced contraction with an IC50 of 2.3±0.04 and 2.7±0.10 mg/ml respectively. The extract (0.32-0.64 mg/ml) also significantly (P<0.001) inhibited potassium chloride-induced contraction with an IC50 of 0.3±0.01 mg/ml. The aqueous extract however, had no significant angiotensin converting enzyme inhibitory activity. Subfractions F11-13, F29, and F30-36 significantly (P<0.05) inhibited acetylcholine-induced contraction of the rat ileum with no significant inhibitory effect on angiotensin II-induced contraction. Furthermore, subfraction F11-13 caused a reduction in blood pressure (BP) at 0.8 mg/ml while subfractions F29 and F30-36 gave no BP reduction at the concentrations tested. Both the inhibitory effect on agonist-induced contraction and blood pressure reduction by the subfractions were lower compared with the aqueous leaf extract of Croton zambesicus. The data obtained from this study revealed that the aqueous leaf extract of Croton zambesicus has hypotensive, diuretic, negative ionotropic and chronotropic effects and smooth muscle relaxant activities mediated possibly via inhibition of both angiotensin 1 receptor and extracellular calcium influx through receptor operated and voltage-dependent calcium vii channels. The phytochemicals present in the extract are possibly responsible for these pharmacological activities which may be beneficial in the management of cardiovascular disorders such as hypertension.
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