COX-2 And HO-1 Are Involved In The Delayed Preconditioning Elicited By Bradykinin In Rat Hearts

BACKGROUND AND AIMThe myocardial injury caused by ischemia/reperfusion is a main reason in cardiovascular disease. After brief episodes of ischemia, heart will increase the tolerance for the following long-time severe ischemia. This phenomenon was first discovered by Murry in 1986, which was called ischemic pretreatment , and also ischemic precondition. To induce myocardial ischemic precondition, it has to make the heart ischemic for many times in advance, which is not reality in clinical application. The researcher tried to obtain the heart protective effect direactly instead of ischemic precondition by analysing the mechanism, which is called pharmacal precondition. We had found lots of drugs simulating ischemic precondition up to now, as adenosine, nitrogen monoxidum, norepinephrine for example, bradykinin is one of these drugs. A period of protection, called classical or early preconditioning, is established immediately after the preconditioning ischemia and wanes within 2-3 hs. A subsequent period of protection, termed "delayed," "second window," or "late" preconditioning, is manifested 12-24 hs following the initial preconditioning stimulus and can last up to 72 hs. Bradykinin is one of the endogenous vasoactive substance, which was found increasing under ischemic precondition and participating in heart protection. The fact that giving exogenous bradykinin will induce early phase heart protection was reported in many studys. The mechanisim might be agitating bradykinin B2 receptor, subsequently activating PKC and opening the mitoK_ATP, finally improving systolic function of ischemic heart. Kositprapa and his colleagues fisrtly found that giving exogenous bradykinin could simulate late phase of myocardial heart protection.Many literatures shew that late phase of heart protection was associated with synthesis of NOsynthase, HSPs, and cyclooxygenase-2. It will improve myocardial energy metabolism, enstabling cytoskeleton and cell volume by activating mitoKATP- We will observe the index as heart systolic function and LDH and infarct size during occlusion corona artery anterior descending branch 30mins following reperfusion 2hs by langendorff methord to study whether COX-2^ HO-1 and mitoKATP involves in late phase heart protection induced by bradykinin.MethodsRat hearts were perfused on a Langendorff apparatus and subjected to 3 Omin-ischemia by corona artery anterior descending branch occlusion followed by 2h-reperfusion (I/R). During the period, We observed index as heart systolic function and LDH and infarct size.ResultsCompared with control group, the index of LVEDP of IS group will be raised [ (30.5±4.1) mmHg vs (11.2±2.3 ) mmHg] while LVDP and ±dP/dtmax will be degraded for reperfusion 120min [30%±8% vs 94%±2%, 35%±6%^ 30%±6% vs 94%±3%, 94%±3%] (/><0.01 ). Compared with IS group , LVEDP of BK group will be degraded to 14.4±4.2 mmHg while LVDP and ±dP/dtmax will be raised to 57%±7%, 60%±7% and 46%±9%, suggesting giving bradykinin for 24h will promote myocardial systolic function recovery. Giving L-NAME or methylene blue in advance can inhibit decrease of LVEDP by bradykinin [19.2±3.0]mmHg> (22.2±4.3 )mmHg] and abrogates the increase of LVDP induced by bradykinin (29%±10%, 37%±11%). Compared with giving bradykinin only , the index LVEDP of the rats giving COX-2 or ZnPPIX before bradykinin will increase from 20.6±3.8 mmHg to 21.4±5.5 mmHg, and LVDP will decrease from 43%±10% to 36%±8%, and also ±dP/dt. Whether giving 5-HD before injecting bradykinin or late , it can abrogates the effect of LVEDP degradation induced by bradykinin (26.0±4.0 mmHg> 21.0±2.6 mmHg) and elevation of LVDP(3O%±11%, 31%t9%).We made ANOVA of heart rate among the groups, obtaining the consequence that F=8.83(P<0.0\) . Bradykinin pretreatment can antagonize the decrease of heart rate induced byischemia. Compared with BK group, the heart rate of the antagonist groups were lower. Aftervariance analysis of coronary artery flow among the groups, we obtain the consequence thatF=41.27 (PO.01) , suggesting that antagonists can abrogate the effect of bradykinin. Myocardialabrogated by antagonists.ConclusionBoth cyclooxygenase-2 and heme oxygenase-1 will participate the late phase of myocardial protection induced by bradykinin, while mitoKATP plays both the trigger and distal effector roles in this pathway.