Influence Of High Epidural Blockade On Plasma TXB₂ And 6-keto-PGF_1α Levels During Acute Myocardial Ischemia Reperfusion Injury In Swine

Objective:To evaluate the effect of TEA on the protection of myocardial ischemia/referfusion injury, we observed the hemodynamic change, plasma TXB2 and 6-keto-PGF1α concentrations,and the change of myocardial ultrastructure during acute myocardial ischemia reperfusion injury. To find a new method to protect the myocardium.Methods:Twenty healthy homestic male swine of the same kind were randomly divided into two groups : group I and group II. Animals in the epidural group (group I; n=10) received 2 ml of epidural 0.5% Bupivacaine; Animals in the control group (group II; n=10) received 2ml of epidural normal saline. The animals were fasting for 12 hours before operation. Referring to the experiment model made by Davis: each of the swine was premedicated intramuscularly with Ketamine 20mgKg-1 and Atropine 0.05 mgKg-1 before fixing them to the operating table. Animals were anesthetized intravenously with Thiopental 10mgKg-1 before trachealing intubation. After the T3-4 puncture of the epidural space with the loss-of-resistance technique an18-gauge catheter was advanced epidurally 5cm. Correct position of the catheter was verified by radioscopy. The spread of the local anesthetic was determined immediately after insertion of the epidural catheter and verification of its correct position by injecting 2ml the solution of Isovist300 1ml and 0.75% Bupivacaine 2ml. The range was T1-6. Anesthesia was maintained with 1% Procaine and 0.1% Scoline. PETCO2, Standard ECG leadⅡ, HR and MAP were monitored. Separate the right femoral and insert the catheter to measure blood pressure directly. The heart was exposed through incision of the breastbone. The right atrium was cannulated to monitor CVP and for transfusion. The left anterior descending coronary artery (LAD) was freed. 2ml of 0.5% epidural Bupivacaine was injected in the the epidural group; 2ml of epidural normal saline was injected in the control group. After 15 minutes, the LAD was occluded and 40 minutes later it was set free. The skin temperature was measured 15 min before epidural injection and after epidural injection. During the operation, Bupivacaine and Normal Saline were injected every 2 hour and CVP was kept at 12cmH2O. The room temperature was controlled at 25℃. Blood samples were taken from right atrium for measurement of plasma TXB2 and 6-keto-PGF1α concentrations before epidural administration, 40min after the arterial occluded, 1, 3 and 5h after reperfusion.Results:(1) The age and weight of animals have no significant difference. (2) MAP,HR,CVP were kept unsignificantly changed in group II but decreased by 22%,25% and 28% in group I respectively compared with those before epidural administration (baselines). (3) The changes of plasma 6-keto-PGF1α concentration: those in group II decreased gradually. Compared with those before administration, there was significant difference just 40 after occluded (P<0.05) . 1 hour after reperfusion there was an increase and significant difference 5 hour afer reperfusion (P<0.01) . (4) TXB2 level and TXB2/6-keto-PGF1α ratio increased gradually in both groups. there was significant difference just 40 after occluded (P<0.05) . And increased significantly 3h and 5h after reperfusion compared with those before epidural administration in both groups(P<0.01). (5) TXB2 level and TXB2/6-keto-PGF1α ratio were higher in group II than those in group I (P<0.05). (6) The incidence of ventricular fibrillation was 1/10 in group I and 4/10 in group II. (7) Before reperfusion in the epidural group the myocardial fiber and arrayed in order and edema, but the configuration was clear; in the control group, the fiber had different length and dissolved locally, the mitochondrion crest ruptured. At 5h after setting free, the myocardial cell nucleus membrane was full and the chromosome integrated in the experimental group; in the control group the cell nucleus membrane disappeared partlyand the chromosome integrated even more. The fiber turbulenced and denaturalized locally.Conclusio...