Car. Vasques et al., Muscarinic agonist properties of the hydrobutanol extract from aerial parts of Waltheria viscosissima St. Hil. (Sterculiaceae) in rats, PHYTOTHER R, 13(4), 1999, pp. 312-317
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.