A potent and nitric oxide-dependent hypotensive effect induced in rats by semi-purified fractions from Maytenus ilicifolia.

The aim of this study is to investigate whether extracts and semi-purified fractions obtained from Maytenus ilicifolia leaves have vascular effects in vivo.We tested the ethanolic supernatant of the infusion (ESI), and the ethanolic supernatant of the aqueous extract (ESAE) on the mean arterial pressure (MAP) and heart rate(HR) of anesthetized rats. Intravenous injection of ESAE caused a dose-dependent effect at 10, 20 and 30 mg/kg, reducing MAP by as much as 52.6 +/- 5.5 mmHg. Only the highest dose of ESAE (30 mg/kg) caused a significant reduction in HR during its hypotensive effect. The effect of ESAE was unchanged by atropine,propranolol, or bilateral vagotomy, but was significantly reduced (80%) in animals continuously infused with L-NAME. In addition, methylene blue and ODQ, as well as the potassium channel blockers tetraethylammonium,4-aminopyridine, and glibenclamide, impaired ESAE-induced hypotension. The ethyl acetate fraction(EAF) obtained from ESAE had a potency at least two times greater than ESAE in MAP, without causing any significant change in HR. The hypotension induced by EAF was circumvented by L-NAME, methylene blue andODQ, strongly reduced by tetraethylammonium and 4-aminopyridine (but not by glibenclamide), and abolished by association of these three potassium channel blockers. Chemical investigation revealed that flavonols, mainly catechin and epicatechin, as well as flavonol glycosides (mono- to triglycosides), and tannins, are the main components of this fraction. Our results demonstrate that preparations obtained from M. ilicifolia present a potent hypotensive effect in vivo, an event predominantly dependent on the nitricoxide/guanylate cyclase pathway.

Activation of muscarinic receptors by a hydroalcoholic extract of Dicksonia sellowiana Presl. HooK (Dicksoniaceae) induces vascular relaxation and hypotension in rats.

Dicksonia sellowiana (Presl.) Hook is a native plant from the Central and South Americas that contain high levels of polyphenols, antioxidant compounds involved in protection against inflammation, cancer and cardiovascular risk. A phytomedicinal preparation obtained from aerial parts of D. sellowiana is currently under clinical evaluation in Brazil against asthma, and has been associated with several other beneficial effects. This study demonstrates that a hydroalcoholic extract obtained from D. sellowiana leaves (HEDS) fully relax, in a concentration-dependent manner, rat aortic rings precontracted with phenylephrine. Moreover, administration of HEDS (10, 20 and 40 mg/kg, i.v.) in anaesthetized rats resulted in a strong but reversible hypotension. Aortic relaxation induced by HEDS was abolished by endothelium removal, by incubation of the nitric oxide synthase inhibitor L-NAME, or the soluble guanylate cyclase inhibitor ODQ. In addition, this effect was partially inhibited by indomethacin (a cyclooxygenase inhibitor) and KT 5730 (a PKA inhibitor). The potassium channels blockade by either tetraethylammonium or charybdotoxin also resulted in a potent inhibition of HEDS-induced aortic relaxation, whereas apamine only slightly reduced it. In addition HEDS-induced relaxation was unchanged by 4-amynopiridine and glibenclamide. The selective muscarinic receptor antagonist atropine counteracted both aortic relaxation and blood pressure reduction generated by HEDS. Experiments using HPLC revealed the presence of high amounts of phenolic compounds in this extract. Taken together, our results reveal that the D. sellowiana possess substances with both in vivo and in vitro activities and that the vascular effect of HEDS involves activation of muscarinic receptors, stimulation of the nitric oxide pathway and opening of calcium-activated potassium channels.