| Objective1. To investigate the dose-dependent cardioprotective effect of morphine preconditioning and choose the best dose.2. To investigate the effect of morphine preconditioning on myocardial remodeling after ischemic reperfusion(I/R) injury.3. To investigate the possible mechanism of morphine preconditioning against myocardial remodeling and offer experimental and theoretical support for morphine preconditioning's clinical use.Methods1. Research for dose-dependent cardioprotective effect of morphine preconditioning. Evaluate the cardioprotective effect of morphine preconditioning by detecting hemodynamics, plasma cardiac troponin I and the infarct size in a rabbit I/R injury model.52 rabbits in which 4 were randomized chosen as sham group and the others were randomized assigned into normal saline (NS) group, morphine preconditioning groups (0.03mg/kg,3.0mg/kg,0.3mg/kg, 1.0mg/kg, 0.1mg/kg) took part in the experiment. The I/R injury model was induced by ligating the left anterior descending (LAD) branch for 30min and then reperfused, but the LAD of S group was just encircled without ligation. NS group rabbits were given 2ml saline 15min before LAD ligation and morphine preconditioning groups received different doses morphine which were diluted to 2ml by saline at the same time point. Hemodynamics, plasma cardiac troponin I and the infarct size were detected at the second day of surgery.2. Observation of the effect of morphine preconditioning on myocardial remodeling after I/R injury. Evaluate the cardioprotective effect of morphine preconditioning on myocardial remodeling by detecting hemodynamics, plasma brain natriuretic peptide (BNP), the heart weight, Masson's staining and heart function in a rabbit I/R injury model after 28day after surgery.6 rabbits were randomized chosed in S group while the other 30 were equally randomized assigned into NS group and M group. Creat I/R injury as the first part. Assessed the rabbit heart function using echocardiogram at 3,7,14,21 and 28day after surgery. Detected hemodynamics, plasma BNP,the heart weight, Masson's staining results 28 days after surgery.3. Observation of the opioid receptor effect on morphine preconditioning against myocardial remodeling. Created the rabbit I/R injury model and interfered with morphine preconditioning and opioid receptor inhibiter naloxone. Evaluate the cardioprotective effect by detecting hemodynamics, plasma brain BNP, and heart function at 1,3,7, 14,28 day after I/R injury also with immunohistostaining of?receptor. AT the last day, the heart weight was balanced.15 rabbits were randomized chosed in S group and the other 165 were randomized assigned into NS, M, NAL, M+NALgroup.6-8 rabbits would be randomized chosed at each time point for detecting the indexes mentioned above.4. Observation of TGF-(31 and p38MAPK expression in the remodeling cardiac tissue treated with or without morphine preconditioning. Cardiac tissue was obtained in the third part. Immunohistostaining and Western Blot methods were used to determine the expression of TGF-?1 and p38MAPK in ischemic region and the remote region, respectively. Resuts1. Morphine preconditioning exhibited a dose-dependent cardioprotective effect manner. Indexes of hemodynamics (MAP, LVESP, dp/dtmax, LVEDP, dp/dtmin) of morphine preconditioning were greater than NS group for M2 and M4 group, especially for M3 group. Plasma concentration of cTnI was lower in all the morphine preconditioning groups campared to NS group. The area at risk size of morphine groups had no difference with NS group, but the infarct size of morphine groups were significantly smaller than NS group while there were no difference among themselves.2. At 28 day after I/R injury, LVEDP, dp/dtmax and dp/dtmin of M group were greater than NS group. Plasma concentration of BNP was lower in M group compared to NS. There was no difference in the rabbit body weight among the three groups. The whole heart weight of I/R group (NS and M group) was heavier that S group. And the LV/body weight ratio of M group was significantly higher than S and NS group, respectively while the RV weight and RV/body weight ratio of NS were higher than the other groups. Masson's staining showed wider collagen fiber in NS group than in M group. The left ventricular ejection fraction (EF) and fraction shorting (FS) were declined both in M group and NS group, but, the EF and FS of M group were higher than NS group at all the observation points except for the 14 day of EF.3. At the second day of I/R injury, indexes of hemodynamics of M group were greater than the other three I/R groups. LVEDP of NAL group was higher than NS while its dp/dtmax was lower compared to NS group. At the 28 day after I/R injury, M group rabbits still showed greater hemodynamics than NS and NAL group. Plasma concentration of BNP of M group were significantly lower than NS and NAL group at 7,14,28 day after cardiac injury, respectively. All of the I/R groups took larger heart/body weight ratio than S group. The RV/body weight ratio of NAL was higher than M and M+NAL group. Immunohistostaining showed that in ischemic region, the?receptor expression was different between NS and M group in 1,3 and 7 day. The?receptor expression was different between M and M+NAL group at 1 day. In the remote region,?receptor expression was different between NS and M group at 14 and 28 day while there was also different?receptor expression between NS and M+NAL group at 28 day.4. Immunohistostaining showed that intensive expression of TGF-?1 emerged at 1 day after I/R injury in ischemic region and 28 day in remote region. And its expression could be promoted by morphine preconditioning at 1 day in ischemic region but inhibited at 28 day in remote region compared to NS group. It is showed that intensive expression of p38 MAPK emerged at 1 day after I/R injury in ischemic region and 28 day in remote region. And its expression could be inhibited by morphine preconditioning both at 1 day in ischemic region and at 28 day in remote region compared to NS group. The results were similar in Western Blot test. Conclusions1. Morphine preconditioning shows dose-dependent cardioprotective effect in the rabbit I/R injury model and the best dose was 0.3mg/kg I.V. before LAD ligation.2. Morphine preconditioning produces prolonged cardioprotection during post-infarction remodeling.3. The effect of morphine preconditioning against myocardial remodeling is mediated by activating opioid receptors, and naloxone could temporarily inhibited the cardioprotection of morphine preconditioning in the acute phase of I/R injury but could not block the cardioprotective effect, especially in the remodeling phase.4. Expression of TGF-?1 and P38MAPK are changed in the situation treated with morphine preconditioning in rabbit myocardial renmodeling model, so the effect of morphine preconditioning against myocardial remodeling may also be mediated by TGF-?1 signaling. |
PDF Full Text Request