Vasodilatation Of Hyperin On Rat Cerebral Basilar Artery And Mechanism

Large arteries such as the basilar artery can make significant impact on cerebrovascular resistance, therefore, playing an decisive role to the microvascular pressure, and the dyfunction of basilar artery may aggravate cerebral ischemic damage. Hyperin(Hyp, a flavonol compound in Abelmoschus manihot) is reported to play protective effects after cerebral ischemia by increasing the rat cerebral blood and reducing the cerebrovascular resistance. Especially, Hyp can relax basilar artery to prevent against ischemia injury.Large-conductance calcium-activated potassium channel(BKca) can regulate the vasomotion function of vascular smooth muscle, however, it is still unknown whether Hyp can promote the BKca channel opening, or whether and to what extent it can effect the expression of BKca protein of basilar artery smooth muscle after ischemia. It is reported that in the coronary artery of pig, Protein kinase C (PKC) can inhibit the activition of BKCa channel induced by UTP, Then in rats basilar artery, it is still worth exploring whether PKC can inhibit the the activition of BKca channel caused by Hyp, which is also one of the experimental purpose.Purpose:1. To investigate the vasodilatation effect of Hyp and the influences of Hyp on BKCa channel on rat cerebral basilar artery. Explore whether PKC play a role in the activition of BKca channel induced by Hyp.2. To verify the role of Hyp on cerebral ischemia reperfusion injury in rats.3. To explore the effect of Hyp on the expression of BKCa β1 subunits in the smooth muscle cells of basilar artery among rats.Methods:1. Rat cerebral basilar artery rings were precontracted with U46619 or KC1 and the vasodilatation effect of hyperin (Hyp) on the artery rings was recorded with the Multi Wire Myograph System Modle, regarding the potassium channel opener (NS1619) as a positive control, endothelium-dependent mechanism was explored by mechanical removal of the endothelium, BKCa channel was investigated by pretreatment of the artery rings with the BKCa channel inhibitor, and Protein kinase C (PKC) was investigated by pre-incubation with PKC activator or inhibitor in the basilar artery rings.2. To establish the middle cerebral artery occlusion (MCAO) model (ischemia for 2h and reperfusion for 24h) in 40 Sprague-Dawley (SD) rats, among which two groups accept the treatment with Hyp before surgery. After 24h of reperfusion, To observe the effects of Hyp on neurological score and the infarction area of brain tissue.3. Apply the Multi Wire Myograph System Modle to study the effect of Hyp on vasorelaxation in MCAO rat basilar artery4. Immunohistochemical staining is used to observe the expression changes of β1 subunits of BKca channel and PKC in rats cerebral basilar artery smooth muscle cells after ischemic injury.Results:1. Hyp produced concentration-dependent relaxation of the endothelium-intact rings which were precontracted with U46619 and KC1. Mechanical removal of the endothelium produced a significant inhibition on Hyp-induced vasodilator response.2. Hyp-induced relaxation could be reduced drastically by BKCa channel inhibitor iberiotoxin (IBTX).3. The promoting effect could be found in the Hyp-induced vasodilatation of artery rings incubated with the PKC inhibitor Bisindolylmaleimide 1 (Bis 1), while PKC activator phorbol 12-myristate 13-acetate (PMA) could inhibit the Hyp-induced vasorelaxation of artery segments.4. Compared with MCAO model group, the Hyp administration groups (50mg/kg,25mg/kg) can reduce the neurological function score and infarction area of brain tissues after cerebral ischemia injury.5. Compared with shame group. Hyp-induced relaxation in MCAO rat cerebral basilar artery could be decreased significantly, But compared with solvent control group, Hyp-mediated obvious relaxtion in MCAO rat cerebral basilar artery.6. As immunohistochemical staining results showed, compared with MCAO model group, The Hyp-treated groups could increase the expression of β1 subunits of BKca channel in cerebral basilar artery smooth muscle cells after cerebral ischemia.In addition cerebral ischemia injury could decrease the expression of β1 subunits of BKCa channel.7. There is no difference in the expression of the protein of PKC of smooth muscle cells between MCAO group and Hyp-treated groups.Conclusion:1. Hyp-induced relaxation on rat cerebral basilar artery is related to the open probability of BKCa channel, Activation of BKCa channels increases K+ efflux, causing hyperpolarization, which is followed by the closure of voltage-dependent Ca2+ channels, reduction of Ca2+ entry and vasodilatation.2. Hyp relaxats cerebral vessels by inhibiting PKC and Hyp may activate BKCa through PKC.3. Hyp has an obvious protect effect of cerebral ischemia injury. Hyp-mediated significant vasorelaxation in MCAO rat cerebral basilar artery4. The expression of BKCa β1 subunits are up-regulated by Hyp in cerebral artery smooth muscle cells(CASMCs)of MCAO rats, which will cause a relaxing effect of cerebral arteries to protect the cerebral ischemic tissues.