Cardiovascular effects of Urtica dioica L. in isolated rat heart and aorta

Urtica dioica L . or Nettle (Urticaceae) is widely used in oriental Morocco to treat hypertension. Aqueous extract of Nettle (AEN) also exerts a hypotensive action in the rat in vivo . The aim of this work was to characterize the specific cardiac and vascular effects of AEN. In the isolated Langendorff perfused rat heart, AEN (1 and 2 g/l) markedly decreased heart rate and increased left ventricular pressure. Higher concentration (5 g/l) even led to cardiac arrest. Although carbachol mimicked the bradycardiac effect of AEN, atropine (a muscarinic receptor antagonist, 1 µM) did not modify the response. Beside its action on myocardium, AEN also affected vascular contractility. Indeed, AEN (0.1–5 g/l) produced a dose‐dependent increase in basal tone of isolated rat aorta. This effect was endothelium independent and was abolished by 1 µM prazosin (an α1‐adrenergic antagonist). AEN had little additional effects when the aorta was precontracted by noradrenaline (1 µM) or KCl (40 mM). Our data indicate that AEN produces a vasoconstriction of the aorta which is due to activation of α1‐adrenergic receptors. However, AEN also induces a strong bradycardia through non‐cholinergic and non‐adrenergic pathways which might compensate for its vascular effect and account for the hypotensive action of Urtica dioica L described in vivo . Copyright © 2002 John Wiley & Sons, Ltd.