|
Objective: A lot of researches have shown that chronic intermittent hypobaric hypoxia (CIHH) has obvious cardiac protection, enhancing resistance of heart to ischemia or hypoxia, diminishing the ischmia/reperfusion injury on myocardium, promoting recovery of cardiac function, and having antiarrhythmia effect. It was reported that CIHH could change the reactivity of the body to some drugs. Anandamide, a kind of endocannabinoid, has a protective effect on heart against ischemia/ reperfusion-induced myocardial damage and arrhythmia, but whether CIHH has effect on the cardiac protection of anandamide is not known. The purpose of present study was to investigate the effect of CIHH on cardiac protection of AEA , and the underlying mechanism.Methods: Adult male Sprague-Dawley rats (n=54) were randomly divided into nine groups: CIHH 14 days group(CIHH14), CIHH 28 days group(CIHH28),anandamide group(AEA), CIHH 14 days with AEA group(CIHH14+AEA) and control group(CON)The rats in CIHH and CIHH+ AEA groups were put into a hypobaric chamber to get 14 days, 28 days CIHH exposure mimicking 5000 m high altitude (PB=404 mmHg, PO2= 84 mmHg), 6 hours per day, respectively. The rats in AEA and CON groups live in same enveronment as CIHH rats except CIHH exposure.The rats were anesthetized with sodium pentobarbital (60 mg/kg, ip). When chest was open the heart was quickly taken out and mounted on a Langendorff apparatus for a retrograde perfusion with Krebs–Henseleit solution (K-H solution). After stablization of perfusion with K-H solution for 20 min the heart underwent 30-min global ischemia followed with 60-min reperfusion. A sack filled with fluid was inserted into left ventricle to record the pressure which was transmited to a record system through pressure transducer. The cardiac functional parameters, including left ventricular develop pressure (LVDP), left ventricular end diastolic pressure (LVEDP), maximal positive and negative velocity of left ventrichlar pressure (±LVdp/dtmax), were recorded under the basical condition and during ischemia/reperfusion, respectively.For isolated rat heart, the different interfere of drugs were given before ischemia, respectively. 1. The rat heart in AEA and CIHH14+AEA groups was perfused with K-H solution comtaining AEA (2 nM) for 15 min before ischmia. 2. For some rats in CIHH14+AEA group, the heart was perfused with K-H solution compaining AM630 (10 nM), an antagonist of CB2 receptor, or AM251 (10 nM), an antagonist of CB1 receptor, for 15 min before AEA, respectively. 3. For some rats in CON group, the heart was perfused with K-H solution compaining AM630 (10 nM), an antagonist of CB2 receptor, or AM251(10 nM), an antagonist of CB1 receptor, for 15 min before AEA, respectively.During the experiment, the activity of lactate dehydrogenase (LDH) in effluent from coronary artery of heart (coronary artery flow) was measured through biochemistry method. At the end of experiment, the heart was taken down and put into liquid nitrogen for preservation. The activity of superoxide dismudase (SOD) and content of malondialdehyde (MDA) in myocardium were assessed through biochemistry method.Result:⑴Under the basal condition,LVDP in CIHH14, CIHH28, AEA, CIHH14+AEA and CON rats was 132.1±9.7, 132.0±12.8, 135.5±8.6, 131.6±8.5 and 132.2±11.0, respectively. LVEDP was 5.5±2.9, 5.6±1.8, 7.8±5.7, 5.8±3.3 and 5.7±2.6, respectively. +LVdp/dtmax was 3606.4±97.1,3616.8±109.2, 3610.3±116.8,3586.6±90.4 and 3617.3±97.9, respectively. -LVdp/dtmax was 2536.4±87.9,2612.0±46.4,2498.4±96.4,2480.4±63.0 and 2500.4±80.4, respectively. Every parameters of cardiac function was not different significantly among groups (P>0.05).⑵At 60 min of ischemia/reperfusion,the recovery of LVDP in CIHH28 and CIHH14+AEA rats was 52.7±6.5% and 53.1±8.5%,with no difference between two groups (P>0.05),but was much better than 11.2±5.9% in CIHH14 rats, 8.9±5.3% in AEA rats and 10.4±4.0% in CON rats, respectively (P<0.01). The recovery of LVEDP in CIHH28 and CIHH14+ AEA rats was 48.3±12.3% and 42.1±11.5%,with no difference between two groups (P>0.05),but was much better than 14.5±10.2% in CIHH14 rats, 15.7±9.7% in AEA rats, and 15.6±9.1% (P<0.05) in CON rats, respectively (P<0.05). The recovery of +LVdp/dtmax in CIHH28 and CIHH14+AEA rats was 38.1±2.2% and 38.2±2.4%,with no difference between two groups (P>0.05),but significantly better than 8.6±1.5% in CIHH14 rats, 8.3%±1.1% in AEA rats, and 8.5±1.5% in CON rats, respectively (P<0.05). The recovery of -LVdp/dtmax in CIHH28 and CIHH14+AEA rats was 41.8±2.4% and 40.5±1.3%, with no difference between two groups (P>0.05),but was significantly better than 11.2±1.7% in IHH14 rats, 11.5±2.1% rats, and 10.7±1.3% rats, respectively (P<0.05).⑶At 60 min of ischemia/reperfusion, LDH in effluent of coronary artery in CIHH28 and CIHH14+AEA rats was 49.3±6.5 and 40.9±5.2, with no difference between two groups (P>0.05),but was obviously lower than 93.7±6.4 in CIHH14 rats, 110.2±8.0 in AEA rats, and 101.6±8.0 in CON rats, respectively (P<0.05). Activity of SOD in CIHH28 and CIHH14+AEA rats was 229.7±6.7 and 239.3±6.2, with no difference between two groups (P>0.05), but was much higher than 160.2±6.7 in CIHH14 rats, 170.7±7.3 in AEA rats, and 181.9±4.4 in CON rats, respectively (P<0.05). The content of MDA in CIHH28 and CIHH14+AEA rats was 1.8±0.1 and 1.3±0.1, with no difference between two groups (P>0.05), but was much lower than 2.1±0.1 in CIHH14 rats, 2.0±0.1 in AEA rats, and 2.2±0.1 in CON rats, respectively (P<0.05).⑷There was no effect of AM251, CB1 receptor antagonist, and AM630, CB2 receptor antagonist, on cardiac function of control rats. Pretreatment with AM630, but not AM251, inhibited the recovery of left ventricular function in CIHH14+AEA rats after ischemia/reperfusion, including LVDP, LVEDP and±LVdp/dtmax, increased LDH in effluent of coronary artery and MDA in myocardium, and decreased SOD in myocardium in CIHH14+AEA rats.Conclusion:⑴CIHH for 28 days can induce cardiac protection, enhancing recovery of function in rat heart from ischemia/ reperfusion, decreasing the activity of LDH in effluent of coronary artery, increasing the activity of SOD and decreasing content of MDA in myocardium of rat.⑵CIHH for 14 days and AEA in low concentration have no cardiac protection, but can promote the cardioprotection of AEA against ischemia/reperfusion injury, enhancing the recovery of cardiac function from ischemia/reperfusion, decreasing activity of LDH in effluent of coronary artery, increasing the activity of SOD and decreasing content of MDA in myocardium of rat.⑶The enhancement of CIHH on AEA cariac protection was blocked by CB2 receptor antagonist,but not CB1 receptor antagonist, which suggests the effect of CIHH on AEA cariac protection may be mediated by CB2 receptor of AEA.
|