The Protective Effects Of Taurine And Its Combination With Enalapril On Isoprenaline-induced Myocardial Injuries In Rats

OBJECTIVE To observe the differences of electrocardiogram (ECG) in anaesthetized and conscious unrestrained rats with myocardial injuries reduced by multi-site subcutaneous injection (sc) of isoprenaline (ISO), the repeatability of the ECG changes in these models if ISO was administrated successively with a given interval, and the protective effect of taurine (Tau), enalapril (ENA) and their combination in conscious unrestrained rats with myocardial ischemia induced by ISO. METHODS ① A rat myocardial ischemia injury model was established by ISO 5.0 mg· kg-1 sc. ② The ECG (LⅡ) was monitored and analyzed by the RM 6240C multichannel physiology signal collection and analysis system in anaesthetized rats, and by the telemetric radio transmitter (TA10CA-F40, Data Science International) in conscious unrestrained rats respectively. The degree of myocardial ischemia was evaluated by the ECG ST segment depression at 0, 1, 3, 5, 10, 30, 60, 120, 180, 240 min after sc ISO and the sums of ST segment depression (∑△S-T ) of all the recorded time except 0 min after sc ISO. ③ The levels of serum Creatine Kinase-MB (CK-MB) and cardiac Troponin I (cTnI) were measured at 22 h after sc ISO to observe the protective effect of Tau and ENA. RESULTS ① Significant depression of ECG ST segments in both anaesthetized rats and conscious unstrained rat models were observed at 1 min after sc ISO, especially at 5 min and 2 h (anaesthetized rats),3 min and 1 h (conscious unstrained rats) respectively. The ∑△S-T of anaesthetized rats was 16.34 ± 1.47 mV, significantly higher than that of conscious unstrained rats (9.84 ± 0.68 mV) (P < 0.01). The ECG recovery time of anaesthetized rats was about 13 hours, much longer than that of conscious unstrained rats (about 4 hours). ② The anaesthetized rats, that had been intravenously injected with isoprenaline, could not wake up until 24 ~ 48 h after sc ISO for the first time, and the livability after sc ISO three times successively with 2 day interval was low (2/10). The ∑△S-T of successive three times of sc ISO in conscious unstrained rats was 9.95 ± 0.84 mV, 9.84 ± 0.75 mV and 9.74 ± 0.93 mV respectively (P > 0.05). ③ Compared with the control group, there are significant inhibition on ECG ST segment depression (P < 0.05) and decreases on serum CK-MB (P < 0.01) and cTnI (P < 0.01) in Tau 200, 400 mg· kg-1· d-1 ip, ENA 2.0 mg· kg-1· d-1 ig, Tau 200 mg· kg-1· d-1 ip + ENA 2.0 mg· kg-1· d-1 ig. There was a more significant improvement of these indexes in Tau + ENA, compared with Tau and ENA alone (P < 0.05). CONCLUSION ① The myocardial ischemia model induced by multi-site sc ISO in conscious unstrained (but not in anaesthetized) rats is good in stability and repeatability and can be applied in studying the effect of anti-myocardial ischemia drugs. ② Taurine protects rat myocardium from isoprenaline-induced injuries, and moreover, there is synergism in inhibiting isoprenaline-induced cardiac injuries when taurine and enalapril are comedicated.