doi: 10.1111/j.1472-8206.2005.00382.x ORIGINAL ARTICLE Radish seed extract mediates its cardiovascular inhibitory effects via muscarinic receptor activation Muhammad Nabeel Ghayur, Anwarul Hassan Gilani* Department of Biological and Biomedical Sciences, The Aga Khan University Medical College, Karachi-74800, Pakistan INTRODUCTION Raphanus sativus Linn. (family, Cruciferae) is a medium sized annual herb commonly known as ‘muli’ in Pakistan and as ‘radish’ in the west. It has been known since the ancient China, Egypt, Rome and Greece. Different parts of the plant such as the seeds, roots and leaves are used in the Sub-Continent in cooking and in a wide variety of ailments. Radish is used by people in different gastrointestinal, biliary, hepatic, urinary, respiratory disorders [1,2] and in cardiovascular diseases such as hypertension [3–5]. Recent research has shown the effectiveness of radish as an antiurolithiatic [6], anti-inflammatory and antibleed- ing [7], influenza protective [8], antimicrobial [9] and antioxidant agent [10]. Phytochemical studies show that radish contains proteins, polyphenols, flavonoids, per- oxidases, isoperoxidases, alkaloids such as pyrrolidine, isoquinoline, phenethylamine and sulphuric compounds such as glucoparin and sinigrin [6]. There are no studies in the literature explaining the cardiovascular effects of the ever popular radish. Thus in this investigation, we report that the hypotensive, cardio-suppressant and vasodilator activities of the seed extract of radish are mediated via activation of choliner- gic receptors. MATERIALS AND METHODS Drugs and standards The following reference chemicals were obtained from the sources specified: acetylcholine chloride, atropine Keywords cardioactive, endothelium-dependent vasodilator, hypotensive, muscarinic, radish Received 13 May 2005; revised 5 July 2005; accepted 10 October 2005 *Correspondence and reprints: anwar.gilani@aku.edu ABSTRACT In this study, we describe the hypotensive, cardio-modulatory and endothelium- dependent vasodilator actions of Raphanus sativus (radish) seed crude extract in an attempt to provide scientific basis for its traditional use in hypertension. The plant extract (Rs.Cr) was prepared in distilled water and was subjected to phytochemical screening using standard analytical procedures. In vivo blood pressure was monitored in anaesthetized normotensive rats. Isolated tissue preparations were suspended in tissue baths containing Kreb’s solution while acute toxicity study was performed in mice for 24 h. Rs.Cr tested positive for the presence of saponins, flavonoids, tannins, phenols and alkaloids and caused a dose-dependent (0.1–3 mg/kg) fall in blood pressure and heart rate of rats that was mediated via an atropine-sensitive pathway. In isolated guinea-pig atria, Rs.Cr showed dose-dependent (0.03–3.0 mg/mL) inhibition of force and rate of contractions. In the atropine-treated tissues, the inhibitory effect was abolished and a cardiac stimulant effect was unmasked which was resistant to adrenergic and serotonergic receptor blockade. In the endothelium- intact rat aorta, Rs.Cr inhibited phenylephrine-induced contractions, which was blocked by atropine and Nx-Nitro-L-arginine methyl ester hydrochloride while was also absent in the endothelium-denuded preparations. The extract was safe in mice up to the dose of 10 g/kg. The study shows that the cardiovascular inhibitory effects of the plant are mediated through activation of muscarinic receptors thus possibly justifying its use in hypertension. ª 2005 The Authors Journal compilation ª 2005 Blackwell Publishing Ltd. Fundamental & Clinical Pharmacology 20 (2006) 57–63 57