Endothelium-dependent and independent vasorelaxation induced by an n-butanolic fraction of bark of Scutia buxifolia Reiss (Rhamanaceae).
BACKGROUND
Scutia buxifolia has been widely used in Brazilian folk medicine as an anti-hypertensive agent. We evaluated the vascular effects and mechanism involved in the relaxation of aorta induced by an n-butanolic fraction (BuOH) from Scutia buxifolia.


METHODS
Rat aortic rings precontracted by phenylephrine (1 μM) were exposed to cumulative concentrations (3–3000 μg/ml) of crude extracts or fractions obtained from bark or leaves of Scutia buxifolia. Classical receptor antagonists, channel and enzymatic inhibitors were used to check the mechanisms involved.


RESULTS
The crude extracts of both leaves and bark of Scutia buxifolia, as well as several fractions, were able to induce partial or total relaxation of rat aortic rings. The BuOH fraction of bark of Scutia buxifolia was the most potent in endothelium-intact (E+) preparations, and also induced a partial, but very significant relaxation in endothelium-denuded (E−) vessels. The non-selective nitric oxide synthase inhibitor L-NAME, as well as the soluble guanylate cyclase inhibitor ODQ, vanished the relaxation in E+. In E− preparations, K+ channel blockers, such as tetraethylammonium, glibenclamide, 4-aminopyridine, and the large-conductance calcium-activated K+ channel blocker iberiotoxin, were able to significantly reduce the maximum relaxation elicited by BuOH fraction.


CONCLUSIONS
Our results demonstrated that BuOH fraction obtained from barks of Scutia buxifolia induced both endothelium-dependent and -independent relaxation in rat aortic rings. The endothelium-dependent relaxation is fully dependent on NO/cGMP system, while direct activation of K+ channels may explain, at least in part, the endothelium-independent relaxation induced by BuOH fraction of Scutia buxifolia.
Department of Pharmacology, UFPR, Brazil.
Rita de C V de A F
Rde C
Da Silva
Sandra
S
Crestani
Priscila
P
de Souza
Aline A
AA
Boligon
Margareth L
ML
Athayde
Adair R S
AR
Santos
Maria Consuelo Andrade
MC
Marques
Cândida A L
CA
Kassuya
José Eduardo
JE
Da Silva-Santos
D020001:1-Butanol / Q000737:chemistry; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000502:physiology; D006152:Cyclic GMP / Q000502:physiology; D004730:Endothelium, Vascular / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009569:Nitric Oxide / Q000502:physiology; D024301:Plant Bark; D010936:Plant Extracts / Q000494:pharmacology*; D018515:Plant Leaves; D024681:Potassium Channels, Calcium-Activated / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D027823:Rhamnaceae; D014661:Vasoconstriction / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology*
D010936:Plant Extracts; D024681:Potassium Channels, Calcium-Activated; D014665:Vasodilator Agents; D009569:Nitric Oxide; D020001:1-Butanol; D006152:Cyclic GMP; D002118:Calcium