Activation of PI3K/Akt pathway mediated by estrogen receptors accounts for estrone-induced vascular activation of cGMP signaling.

Estrone (E1) produces remarkable vascular effects, including relaxation, modulation of proliferation, apoptosis and cell adhesion. This study investigated the role of estrogen receptors and endothelial signaling pathways in the vascular relaxation promoted by E1. Aortic rings from male Wistar rats (250-300 g) were contracted with phenylephrine and stimulated with graded concentrations of E1. The concentration-dependent relaxation induced by E1 was abolished after removal of the endothelium or incubation with the estrogen receptor antagonist ICI 182,780. G protein-coupled estrogen receptor antagonism did not alter the E1 effect. Pretreatment of endothelium-intact arteries with inhibitors of nitric oxide synthase, guanylyl cyclase, calmodulin (CaM) and PI3K reduced the E1-induced vasorelaxation. Incubation with inhibitors of the MEK/ERK1/2 or p38MAPK pathways did not alter the E1 vasorelaxation. Similarly, inhibition of cyclooxygenase or blockade of potassium channels did not change the E1 effect. Western blot analysis evidenced that E1 induces phosphorylation of eNOS, PI3K and Akt in rat aorta. Our data demonstrate that E1 induces aortic vascular relaxation through classic estrogen receptors activation on the endothelium. We also identify CaM and PI3K/Akt pathways as critical mediators of the NO-cGMP signaling activation by E1. These findings contribute to the notion that this estrogen regulates arterial function and represents another link, besides 17ß-estradiol (E2), between postmenopause and vascular dysfunction.

The vasorelaxant effect of gallic acid involves endothelium-dependent and -independent mechanisms.

The mechanisms of action involved in the vasorelaxant effect of gallic acid (GA) were examined in the isolated rat thoracic aorta. GA exerted a relaxant effect in the highest concentrations (0.4-10mM) in both endothelium-intact and endothelium-denuded aortic rings. Pre-incubation with L-NAME, ODQ, calmidazolium, TEA, 4-aminopyridine, and barium chloride significantly reduced the pEC50 values. Moreover, this effect was not modified by indomethacin, wortmannin, PP2, glibenclamide, or paxillin. Pre-incubation of GA (1, 3, and 10mM) in a Ca(2+)-free Krebs solution attenuated CaCl2-induced contractions and blocked BAY K8644-induced vascular contractions, but it did not inhibit a contraction induced by the release of Ca(2+) from the sarcoplasmatic reticulum stores. In addition, a Western blot analysis showed that GA induces phosphorylation of eNOS in rat thoracic aorta. These results suggest that GA induces relaxation in rat aortic rings through an endothelium-dependent pathway, resulting in eNOS phosphorylation and opening potassium channels. Additionally, the relaxant effect by an endothelium-independent pathway involves the blockade of the Ca(2+) influx via L-type Ca(2+) channels.

Endothelium-Dependent Vasorelaxant Effect of Butanolic Fraction from Caryocar brasiliense Camb. Leaves in Rat Thoracic Aorta.

Caryocar brasiliense Camb. "pequi" is a native plant from the Cerrado region of Brazil that contains bioactive components reported to be antioxidant agents. Previous work has demonstrated that dietary supplementation with pequi decreased the arterial pressure of volunteer athletes. We found that the crude hydroalcoholic extract (CHE) of C. brasiliense leaves relaxed, in a concentration-dependent manner, rat aortic rings precontracted with phenylephrine, and that the butanolic fraction (BF) produced an effect similar to that of the CHE. Aortic relaxation induced by BF was abolished by endothelium removal, by incubation of the nitric oxide synthase inhibitor L-NAME, or the soluble guanylatecyclase inhibitor ODQ. However, incubation with atropine and pyrilamine had no effect on the BF-induced vasorelaxation. Moreover, this effect was not inhibited by indomethacin and tetraethylammonium. The concentration-response curve to calcium in denuded-endothelium rings was not modified after incubation with BF, and the vasorelaxation by BF in endothelium-intact rings precontracted with KCl was abolished after incubation with L-NAME. In addition, administration of BF in anesthetized rats resulted in a reversible hypotension. The results reveal that C. brasiliense possesses both in vivo and in vitro activities and that the vascular effect of BF involves stimulation of the nitric oxide/cyclic GMP pathway.