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Interaction between paracrine tumor necrosis factor-alpha and paracrine angiotensin II during myocardial ischemia
I Frolkis1, J Gurevitch, Y Yuhas
1Department of Thoracic and Cardiovascular Surgery, Tel Aviv Medical Center, Israel.
Objectives:
The purpose of this study was to explore interactions between paracrine angiotensin II (Ang-II) and tumor necrosis factor-alpha (TNF-alpha) during myocardial ischemia.
Background:
Ischemic myocardium releases significant amounts of TNF-alpha. This paracrine release correlated with postischemic myocardial injury. Other studies showed myocardial protection obtained by the use of angiotensin-converting enzyme inhibitors (i.e., captopril) and the Ang-II type 1 receptor antagonist losartan after ischemia. The possibility that these agents decrease TNF-alpha synthesis has not yet been investigated.
Methods:
Using the modified Langendorff model, isolated rat hearts underwent either 90 min of nonischemic perfusion (control group) or 1 h of global cardioplegic ischemia. In both groups, either captopril (360 micromol/liter) or losartan (182.2 micromol/liter) was added before ischemia. The hearts were assayed for messenger ribonucleic acid (mRNA) expression and effluent TNF-alpha levels. In addition, cardiac myocytes were incubated in cell culture with Ang-II.
Results:
After ischemia, TNF-alpha mRNA expression intensified from 0.63 +/- 0.06 (control group) to 0.92 +/- 0.12 (p < 0.03), and effluent TNF-alpha levels were 711 +/- 154 pg/ml. The TNF-alpha mRNA expression declined to 0.46 +/- 0.07 (p < 0.01) and 0.65 +/- 0.08 (p < 0.02) in captopril- and losartan-treated hearts, respectively. Effluent TNF-alpha was below detectable levels. Concentrations of TNF-alpha in supernatants of incubated cardiac myocytes treated with 10 and 50 nmol/liter of Ang-II were 206.0 +/- 47.0 pg/ml and 810 +/- 130 pg/ml, respectively (p < 0.004). When pretreated with 700 micromol/liter of losartan, TNF-alpha was below detectable levels.
Conclusions:
This study presents an original explanation for previously reported myocardial protection after ischemia, obtained by the use of captopril and losartan. These drugs reduce TNF-alpha synthesis, providing strong evidence of active interactions between paracrine TNF-alpha and Ang-II in the evolution of the ischemic cascade.