Influence of the Angiotensin II AT1 Receptor Antagonist on Reperfusion Injury in Rat Myocardial Ischemia Model

BACKGROUND AND OBJECTIVES: The protective effect of angiotensin converting enzyme (ACE) inhibitor against ischemia/reperfusion injury has been demonstrated in animal models, however the effect of AT1 receptor antagonist is contradictory. The present study was designed to investigate the myocardial protective effects of the AT1 receptor antagonist irbesartan during myocardial ischemia/reperfusion in vivo. MATERIALS AND METHODS: Sprague-Dawley rats were subjected to a 45-minute left coronary artery ligation followed by a 2-hour re-perfusion. An inert vehicle (group I:n=14) or irbesartan (50 mg/kg/day:group II, n=12) was administered for 3 days before coronary occlusion. The ratio of the myocardial infarct area to the ischemic area at risk was assessed through triphenyltetrazolium chloride staining. Apoptosis was evaluated by analyzing DNA fragmentation and TdT-mediated dUDP nick end labeling staining. Western blot analysis was performed for MAP Kinases (ERK1/2 and p38) and Bcl-2 and Bax. RESULTS: The ratio of the infarct area to the ischemic area at risk of group II was smaller than that of group I (42.6+/-2.7% vs. 64.1+/-4.6%;p<0.005). Agarose gel electrophoresis revealed discrete DNA laddering in the ischemic zone of group I, however DNA ladder formation was attenuated in group II. The expressions of ERK1 MAPK and Bcl-2 were increased in the ischemic area of group II compared to that of group I. CONCLUSION: AT1 receptor antagonist was effective in reducing myocardial reperfusion injury in vivo. This effect can at least be partially attributed to the attenuation of cardiomyocyte apoptosis, and this anti-apoptotic effect appears to be related to the increased expression of Bcl-2 and alterations in MAP kinase signaling.

Association between betaARK1 Level of Circulating Mononuclear Leukocytes and Left Ventrcular mass in Non-treated Hypertensive Patients

BACKGROUND: Beta-adrenergic receptor Kinase 1(betaARK1) is a serine/threonine kinase attached, which inhibits the coupling of beta-adrenergic receptor with G-protein. Myocardial betaARK1 level is usually elevated in heart failure and hypertrophy, but it is not known whether the circulating betaARK1 level is related with the degree of cardiac hypertrophy. This study was performed to evaluate the association of the betaARK1 level in circulating mononuclear leukocytes(MNL) in untreated hypertension with left ventricular mass in hypertensive patients. Method: Nineteen non-treated hypertensive patients were included for this study. High blood pressure was confirmed when systolic BP is over 150 mmHg or diastoli BP is over 95 mmHg. Echocardiography was performed to evaluate the degree of hypertrophy by measuring the left ventricular mass index(LVMI) and relative wall thickness(RWT), and test the LV function by measuring the ejection fraction(EF) according to ASE guideline. At the same time, blood was collected from each patient and MNL were isolated by gradient centrifuge with Ficoll-400. Total RNA was purified from MNL and semi-quantitative RT-PCR was performed. After reverse transcription, PCR was done with primers for human betaARK1 and GAPDH as external control. betaARK1 levels were expressed by ratio to GAPDH level and estimated the relations with clinical and Echocardiographic parameters. Result: We studied confirmed 19 hypertensive patients(10 men and 9 women, mean age of 50.6 years). Echocardiographically measured indices(mean+/-SD) were as follows; LVMI(137.3+/-30.6g/m2), PWT(0.53+/-0.09) and EF(54.6+/-8.5%). Ratio of betaARK1 levels to GAPDH was from 0.10 to 0.96 (0.62+/-0.25). betaARK1 levels were correlated with LVMI(correlation coefficient: r=.502, p=.029) and RWT(r=.627, p=.004). But Systolic BP(r=0.009, p=.93), diastolic BP(r=.07, p=.85) or EF(r=.045, p=.84) were not related to level of betaARK1. CONCLUSIONS: The betaARK1 level of circulating MNL was correlated well with the degree of the cardiac hypertrophy estimated by LVMI and RWT. This data suggests that activation of sympatho-adrenal system would exert a major role in developing cardiac hypertrophy and we can expect the decreased responsiveness to catecholamine in the heart of hypertensive patients. betaARK1 in circulating MNL might be used as a predictor or marker for LV hypertrophy in hypertensive patients.

Sublingual Nitrate-Augmented Redistribution in Thallium-201 Myocardial Perfusion SPECT Compared with Repeated Injection to Detect Viable Myocardium

BACKGROUND: To assess the myocardial perfusion state after myocardial infarction, Tl-201 SPECT (Thallium-201 Single Photon Emission Computed Tomography) with a repeated "booster" injection before the acquisition of delayed redistribution image is more sensitive and more effective than conventional 4 hour redistribution image. However, this protocol has several disadvantages such as patient inconvenience, additional Tl-201 dose and compromised quantitative analysis. In this study, we compared 4 hour nitrate-augmented redistribution protocol with standard 24 hour delayed redistribution protocol with reinjection to evaluate the usefulness of sublingual nitrate to augment myocardial perfusion and the effectiveness of myocardial assessment for each protocol. METHODS: In 20 myocardial infarction patients, stress-redistribution Tl-201 SPECT was performed. Immediately after resting redistribution image was taken, each patient was administered 0.6 mg of nitroglycerin sublingually without additional Tl-201 and nitrate-augmented SPECT was taken after 30 minutes. Each patient then returned the next day and was injected with a booster dose of Tl-201 30 minutes before the delayed redistribution SPECT acquisition. For the analysis of SPECT study, the myocardium was divided into 22 segments, and the perfusion to each segment was scored on a four-point scale by consensus. An overall cardiac perfusion score was derived by summing the perfusion score for each segment. RESULTS: Reduced stress perfusion was identified in 258 segment among total 440 segments: 61 (23.6%) had improved perfusion after rest redistribution; 145 (56.2%) had improved perfusion after nitrate-augmented redistribution; 140 (54.2%) had improved perfusion after 24 hour delayed redistribution after Tl-201 reinjection. The cardiac perfusion score after stress was 38.2+/-13.1. The score increased to 41.5+/-13.1 after rest redistribution. The perfusion score were improved to 46.3+/-10.4 (p< or =0.05 vs. rest redistribution) after nitrate augmentation. The cardiac perfusion score, 46.2+/-10.8, did not improve further after delayed redistribution. CONCLUSION: Tl-201 SPECT with sublingual nitrate-augmented redistribution is as same or better than 24-hour delayed redistribution with reinjection to detect viable myocardium. Therefore, Tl-201 SPECT with sublingual nitrate-augmented redistribution has economic and time sparing advantage over traditional 24 hour delayed redistribution with reinjection.