Muscarinic agonist properties of the hydrobutanol extract from aerial parts of Waltheria viscosissima St. Hil. (Sterculiaceae) in rats

The cardiovascular effects of the hydrobutanol phase of the ethanolic extra ct from the aerial parts (HBWV) of Waltheria viscosissima A. St. Hil. (Ster culiaceae) were tested in rats by using a combined (in vivo and in vitro) a pproach. HBWV (5, 7.5, 10, 15 and 20 mg/kg, randomly) induced a significant and dose-dependent hypotension and bradycardia in conscious freely moving normotensive rats. Both hypotensive and bradycardic effects evoked by a sub maximal dose of HBWV (10 mg/kg) were inhibited by pre-treatment of the anim als with atropine (2 mg/kg, i.v.). In anaesthetized animals, electrocardiog ram recordings revealed second and third degree sinoatrial and atrioventric ular blockade induced by the extract (10 mg/kg, i.v.), which were inhibited by cardiac muscarinic blockade (atropine, 2 mg/kg, i.v.). In isolated rat aortic rings, increasing concentrations of HBWV (50, 100, 200 and 400 mu g/ mL) were able to antagonize the contractile effects of noradrenaline (1 mu M) This effect was inhibited by pre-incubation of the aortic rings with atr opine (1 mu M), by removal of the vascular endothelial tissue or by nitric oxide synthase blockade. These results suggest that both cardiac and periph eral actions induced by HBWV are probably mediated by stimulation of cardia c and endothelial muscarinic receptors, respectively, Copyright (C) 1999 Jo hn Wiley & Sons, Ltd.