Smooth Muscle Relaxant Activity of The Aqueous Leaf Extract of Croton Zambesicus Linn (Euphorbiaceae) In Laboratory Animals

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Basic & Clinical Pharmacology & Toxicology


Croton zambesicus Muell Arg. (Euphorbiaceace) (CZ) is used by traditional medicine practitioners in Nigeria to treat a variety of ailments including hypertension. We confirmed the hypotensive activity in laboratory animals of the aqueous leaf extract of CZ (unpublished work). Aim: To determine the smooth muscle relaxant activity and mechanism of action of the aqueous leaf extract of CZ in laboratory animals. Methods: The effects of aqueous leaf extract of CZ on spontaneous contractions of rabbit ileum and on rat ileum precontracted with Ach (1 lM), angII (1 nM–1 lM), CaCl2 (1–30 mM) and K+ (80 mM) were determined. Results: Spontaneous contractions of rabbit ileum were reduced in a concentration-dependent manner by CZ aqueous extract (3–6 mg/ml) with a maximal reduction of 70 _ 3 %. In the rat ileum CZ aqueous extract inhibited AngII-induced contraction in two phases. A Concentration- dependent inhibition of up to 60 _ 12 % was obtained with 0.6 mg/ml. The second phase inhibition of 98 _ 4 % was obtained with CZ concentration of 6 mg/ml. This effect was similar to that produced by valsartan, a non-competitive antagonist of angiotensin 1 receptor (AT1-receptor). Furthermore, KCl-induced contraction was blocked completely by 0.6 mg/ml CZ leaf extract. CZ extract (1– 6 mg/ml) caused a concentration-dependent inhibition of CaCl2 and Ach-induced contraction of the rat ileum, with a maximal inhibition of 95 _ 2 % and 80 _ 18 % respectively. Conclusion: The aqueous leaf extract of CZ has smooth muscle relaxant activity mediated via inhibition of AT1-receptors and calcium influx through calcium channels, thus providing a pharmacologic basis for use of the plant as antihypertensive in traditional medicine. This study also reveals that CZ acts via multiple pathways, which is in line with the current therapy for hypertension that encompasses the use of drugs with complementary mechanisms of action.



Croton zambesicus Muell Arg