Active renin and angiotensinogen in cardiac interstitial fluid after myocardial infarction

The renin-angiotensin system promotes cardiac hypertrophy after myocardial infarction. The purpose of this study was to measure renin and angiotensinogen in plasma and myocardium 10 days after myocardial infarction. Infarction involving 45 +/- 4% of left ventricular circumference with accompanying hypertrophy was induced in rats (n = 14). Plasma and myocardial renin were increased after infarction compared with sham controls (n = 8) (27.4 +/- 3.2 vs. 7.5 +/- 1.8 ng ANG I.ml plasma.h(-1), P < 0.0002; and 8.8 +/- 1.6 vs. 2.5 +/- 0.1 ng ANG I.g myocardium(-1).h(-1), P < 0.008, respectively). After infarction, myocardial renin was correlated with infarct size (r = 0.62, P < 0.02) and plasma renin (r = 0.55, P < 0.04). Plasma angiotensinogen decreased in infarct animals, but myocardial angiotensinogen was not different from shams (1.1 +/- 0.08 vs. 2.03 +/- 0.06 nM/ml plasma, P < 0.002; and 0.081 +/- 0.008 vs. 0.070 +/- 0.004 nM/g myocardium, respectively). In conclusion, myocardial renin increased after infarction in proportion to plasma renin and infarct size, and myocardial angiotensinogen was maintained after infarction despite decreased plasma angiotensinogen and increased levels of myocardial renin.