Effect Of Tanshinone ?A On Myocardial ET-1 And Its Receptor In Hypertensive Rats Induced By Chronic Intermittent Hypoxia

Obstructive sleep apnea syndrome(OSAS)is a common sleep~related breathing disorder,characterized by snoring and apnea during sleep and shallow sleep,night recurring disorder of hypoxemia and sleep structure.OSAS patients of long~term fluctuations of arterial oxygen saturation,it is resulting in chronic intermittent hypoxia(CIH),which has a comprehensive damage on multiple systems of the body.Modern medicine of OSAS commonly used drug treatment,oral apliance therapy,Continuous Positive Airway Pressure therapy,surgical treatment and so on,but so far,there is no one can completely cure this disease.Tanshinone IIA(Tan IIA)is a lipid~soluble phenolic component of Danshen.It was been reported to reduce myocardial infarction size and show anti~atherosclerosis activity.Besides,Tan IIA was also been known to reduce myocardial oxygen consumption,inhibited platelet aggregation and blood coagulation,expand coronary artery and increase blood flow,and therefore improve the myocardial tolerance to hypoxia.Moreover,it also has anti~inflammatory and anti~oxidant properties.Many studies have reported that CIH can damage endothelial cells,leading to endothelial dysfunction,increased ET-1 synthesis and decreased degradation;the level of ET-1 increased with CIH induced hypertension.Recently,the animal experiments confirmed that the inhibition of Tan IIA on the synthesis of ET-1.It was been showed the effect of ET-1 receptor antagonist in some extent,which improved vascular endothelial dysfunction.Although it is numerous the research of Tan IIA in protecting endothelial function and heart function,and then it is not yet clear that theprotection caused by chronic intermittent hypoxia vascular endothelial cell damage,also did not find the CIH mediated signaling pathway and reports of its receptor expression of ET-1.This study is to investigate the protective effect of Tan ?A as ET-1receptor blockers or inhibitors of chronic intermittent hypoxia~induced myocardial injury in rats with hypertension.Objective:Focused on the hot spots of CIH and its receptor antagonist ET-1,and investigate the effect of Tan IIA on the level of ET-1 on hematoplasma,hemodynamics and myocardial morphology in rats with CIH induced hypertension.Finally,clarify that the mechanism of the effect of Tan IIA on CIH.Methods:Sprague~Dawley(SD)rats(Male,weight is 180~220g,purchased from the Laboratory Animal Center of Hebei Medical University)were randomly been separated into three groups: normoxia group(n=16),CIH group(n=16)and CIH+Tan IIA group(n=16).CIH was been induced by exposing animals to 90 s hypoxia(9% O2 at the nadir)and 90 s normoxia for 8 h/day for 21 consecutive days.Rats in the normoxia group were been kept under normoxic conditions.Systolic blood pressure of rat's tail artery was recorded the day before the modeling(at 17 o'clock)and thereafter at regular intervals of every 2 days.Inner canthus blood was been collected the day before and after the modeling for measurement of blood index.The day after the modeling,animals(n=8)were intraperitoneally injected with urethane(5mg/kg)and the right common carotid artery was isolated.The animals were then been infused with 0.3% heparin saline through venous catheter needle(inner diameter 0.8 mm).After left ventricular catheter placement,the Heart Rate(HR),Left Ventricular Contraction Internal Pressure(LVSP),Left Ventricular End Diastolic Pressure(LVEDP),and maximum ascending and descending rate of Left VentricularPressure(±dp/dtmax)were recorded.The rats in normoxia and CIH groups(n=8)were injected with ET-1(0.03 nmol/kg)through femoral veins and the maximum LVSP was recorded.Tan IIA(0.03 nmol/kg)was given 10 min after the recovery of LVSP to the normal conditions,then ET-1(0.03 nmol/kg)was given 20 min later,and the maximum LVSP was recorded to calculate the CIH-induced contraction.The rats were then been executed and the left ventricle was dissected to obtain the left ventricular mass index(LVWI).Finally,the histopathological analysis of heart tissue was been performed by Hematoxylin-Eosin(HE)staining.Results:1 Effects of Tan IIA on the tail arterial pressure of CIH ratsAfter modeling three weeks,and normoxia group,CIH group rat tail artery pressure(149±4 mmHg)increased significantly(P < 0.05);compared with the CIH group,CIH+Tan IIA group of rat tail artery pressure(119±3 mmHg)were significantly lower(P < 0.05).2 Effects of Tan IIA on body weight(BW),heart mass index(HWI)and left ventricular mass index(LVWI)of CIH ratsThe body weight(313±10 g)in CIH group was significantly lower than the normoxia group(P < 0.05).Compared with CIH group,there was no difference in body weight(331±8 g)between CIH+Tan IIA group rats.Each group were not significantly differences in HWI(3.14±0.05,3.08±0.07,3.06±0.08 mg/g)and LVWI(2.06±0.09,1.98±0.08,2.08±0.11mg/g).3 Effects of Tan IIA on hemodynamics of CIH ratsThe LVSP and LV ± dp / dtmax increased significantly in CIH group rats to compare with normoxia group(P <0.05);the CIH+Tan IIA group rats were significantly lower than the CIH group(P <0.05).4 Effects of Tan IIA on ET-1 induced LVSP changesAfter the injection of ET-1,the LVSP in the normoxia group and CIH group were significantly higher(120±3,148±6 mmHg,P < 0.05).The rate of LVSP change in CIH group was significantly higher than thatin the normoxia group(P < 0.05).The ET-1 induced increases in LVSP were been significantly reduced after Tan IIA injection(P < 0.05).Further injection of ET-1 caused significant higher change in LVSP in CIH rats than that of the normoxia group(P < 0.01).5 Effects of Tan IIA on myocardial histology of CIH ratsHE staining showed that the myocardial cells in CIH group arranged disorderly,with the nuclear contracted.There was obvious proliferation of connective tissue and fibroblasts with visible congestion.In the normoxic group,myocardial cells arranged in neat and showed clear texture.Myocardial cells in the CIH+Tan IIA group arranged neatly when compared with CIH group.The cells were rod~shaped,light coloured,and showed uniform nuclear chromatin distribution and fibroblasts arrangement.6 Effects of Tan IIA on plasma ET-1 and serum NO levels of CIH ratsThe plasma ET-1 levels of CIH group were significantly higher than the normoxia group,while serum NO content was significantly lower(P< 0.05).There were the plasma ET-1 levels of the CIH+Tan IIA rats significantly lower and the serum NO content was significantly higher than CIH group(P < 0.05).7 Effects of Tan IIA on ET-1,ETA and ETB receptor expression in cardiac muscle of CIH ratsThe expression of ET-1 and ETA receptor in CIH group was significantly higher than that in the normoxia group,while the expression of ET-1 and ETA in CIH+Tan IIA group was significantly lower than that in CIH group.8 Effects of Tan IIA on the expression of eNOS,ET-1 and its receptor in myocardium of CIH ratsThe protein expression of ET-1 and ETA receptor were significantly increase in CIH group to compare with normoxia group,while the protein expression of ET-1 and ETA receptor in CIH+Tan IIA group wassignificantly lower than that in CIH group.The protein expression of ETB receptor in the CIH group was significantly lower than that in the normoxia group,while the ETB receptor in the CIH+Tan IIA group was higher than that in the CIH group.Meanwhile,the protein expression of eNOS in CIH group was lower than that in normoxia group,higher than CIH group.Conclusion: Tan II A can reduce the chronic intermittent hypoxia induced hypertension,and by inhibiting the expression of ET-1 induced by CIH in order to protect the myocardial injury caused by CIH.