Reoxygenation and calcium-induced cerebroarterial contractions as affected by vasodilator agents

Endothelium-dependent vasodilatation effects of the essential oil from Fructus alpiniae zerumbet (EOFAZ) on rat thoracic aortic rings in vitro

Fructus Alpiniae Zerumbet (FAZ) is an herb widely used to treat vascular disorders in Guizhou province, China, the essential oil has been identified as one of it vasodilation effect active components, and especial, the composition was significantly difference from the leaves. Vasodilation effects and mechanism of essential oil from FAZ (EOFAZ) were investigated. The EOFAZ showed significant vasodilation effect on endothelium-with rat thoracic aortic rings preincubated with norepinephrine (NE, 1.0μM) or KCl (60mM) in a concentration-dependent manner (1.14-72.96μg/ml). The non-selective nitric oxide synthase inhibitor l-NAME, as well as the soluble guanylate cyclase inhibitor MB, attenuated the relaxation of EOFAZ in endothelium-intact rat thoracic aortic rings. However, there were not significantly affected the vasodilation effects pretreated with cyclooxygenase inhibition by indomethacin (Indo) or β-noradrenergic inhibition by propranolol (Prop). The present results first demonstrated that vasodilation effect of EOFAZ depending upon the endothelium and concentration, and the mechanism involvement of NOS-cGMP system. In contrast, prostacyclin and β-adrenoceptor may not be associated with EOFAZ-induced vasorelaxation.

Vasodilatory effects of cinnamaldehyde and its mechanism of action in the rat aorta

The vasodilatory effect of cinnamaldehyde was investigated for its mechanism of action using isolated rings of rat aorta. Cinnamaldehyde relaxed aortic rings precontracted with phenylephrine in a dose-dependent manner, was not affected by either the presence or removal of the endothelium. Pretreatment with NG-nitro-L-arginine methyl ester and 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one could not block vasodilation by cinnamaldehyde, indicating that nitric oxide signaling is not involved. Potassium channel blockers, such as glibenclamide, tetraethylammonium, and BaCl₂, had no effect on the relaxation produced by cinnamaldehyde. In addition, treatment with either indomethacin or propranolol did not affect cinnamaldehyde-induced vasodilatation. On the other hand, pretreatment of endothelium-denuded rings with cinnamaldehyde significantly inhibited vasoconstriction induced by endogenous vasoconstrictors, including angiotensin II, 5-hydroxytryptamine, dopamine, endothelin-1, and phenylephrine. In a Ca²⁺-free experimental setting, this natural vasodilator not only blocked Ca²⁺ influx-dependent vasoconstriction by either phenylephrine or KCl, but also inhibited phenylephrine-induced tonic contraction, which relies on intracellular Ca²⁺ release. This study shows that endothelium-independent, Ca²⁺ influx and/or an inhibitory release mechanism contributes to the vasodilatory effect of cinnamaldehyde.

Vascular dilation by paeonol--a mechanism study

The goal of this study was to investigate the mechanism underlaying the vasodilatory effect of paeonol, a major active element from the root bark of Chinese herbs Paeonia suffruticosa Andr. and Cynanchum paniculatum (Bunge) Kitagawa. Paeonol relaxed isolated rat aorta rings by 95.6% while the 10(-6) M forskolin-induced vasodilatation used as 100%. The EC(50) of vasodilatation by paeonol is 2.9x10(-4) M. Although paeonol exerted endothelium-independent relaxation, L-NAME treatment inhibited paeonol-induced vasodilation of endothelium intact rings, while indomethacin did not. Both L-NAME and ODQ did not affect paeonol relaxation in the rings without endothelium. In addition, paeonol markedly elevated NO generation in cultured endothelial cells. Pre-treatment of propranolol, glibenclamide, TEA and BaCl(2) did not affect paeonol relaxation of endothelium removed rings. On the other hand, pre-treated of rings (without endothelium) with paeonol markedly blocked vasoconstriction induced by AngII, PGF(2alpha), 5-HT, dopamine, vasopressin, endothelin-1 and PE. The paeonol incubation also significantly attenuated KCl-induced contraction which mainly depended on Ca(2+) influx. In Ca(2+)-free medium (containing 10(-4) M of EGTA and 60 mM of KCl), paeonol suppressed the contraction curve of CaCl(2). In addition, paeonol also inhibited contraction by PE in Ca(2+) free solution (containing 10(-4) M of EGTA) which mainly relied on intracellular Ca(2+) release. Whole-cell patch-clamp experiment showed that paeonol shifted the I-V curve and the peak value of calcium currents was significantly inhibited. In conclusion, our study suggested that voltage-dependent and receptor-operated Ca(2+) channel, as well as intracellular Ca(2+) release were all inhibited by paeonol. An intracellular Ca(2+) regulatory mechanism may be responsible to potent vasodilatory effect of paeonol.

The effects of beraprost Na, a stable prostacyclin analog, on animal models of stroke

We evaluated the effects of beraprost Na (Sodium (+-)-(1R*,2R*, 3aS*,8bS*)-2,3,3a,8b-tetrahydro-2-hydroxy-1-[(E)-(3S*)-3- hyd roxy-4-methyl-1- octen-6-ynyl]-1H-cyclopenta[b]benzofuran-5-butylate, beraprost), a stable and orally active prostacyclin (PGI2) analog with potent antiplatelet and vasodilating properties, on two stroke models, namely sudden death induced by arachidonate (AA) in rabbits and spontaneous stroke in stroke-prone spontaneously hypertensive rats (SHRSP). In the AA-induced sudden death model, 30 min after beraprost administration (1 or 3 mg/kg, po), AA was injected into the rabbit internal carotid artery, and incidence of convulsion and sudden death were assessed. Beraprost decreased both incidence of convulsion and mortality of rabbits. In SHRSP, orally administered beraprost (100 micrograms/kg, twice a day from 56-385 d of age) improved survival rate and decreased incidence of stroke. Preventive effects of beraprost on the two stroke models may have been caused mainly by the improvement of cerebral circulation. These results indicate that beraprost may have potential in the treatment and/or prevention of the cerebral circulatory disorders.

Action of atrial natriuretic peptide (ANP) on dog cerebral arteries: evidence that neurogenic relaxation is not mediated by release of ANP

1. Atrial natriuretic peptide (ANP) (10(-9) to 10(-8) M) produced a concentration-related relaxation in helical strips of dog cerebral arteries partially contracted with prostaglandin F2 alpha. The relaxation was not affected by treatment with ouabain, quinidine, oxyhaemoglobin, methylene blue, or removal of endothelium. 2. Relaxations induced by nicotine or transmural electrical stimulation were not reduced in arteries in which tachyphylaxis to ANP had developed. 3. In arteries exposed to Ca2+-free media under severe hypoxia, contractions due to prostaglandin F2 alpha and Ca2+ were attenuated by treatment with ANP, whereas the reoxygenation-induced contraction was unaffected. 4. The results suggest that ANP does not mediate neurogenic relaxation of dog cerebral arteries. The ANP-induced relaxation is not associated with activation of the sodium pump but is due to an inhibitory action on the release and influx of Ca2+, probably as a result of stimulation of guanylate cyclase.