CARDIAC ANGIOTENSIN-CONVERTING ENZYME OVERPRODUCTION INDICATES INTERSTITIAL ACTIVATION IN RENOVASCULAR HYPERTENSION

Angiotensin converting enzyme (ACE) activity in the plasma does not ch ange significantly with hypertension in two-kidney, one-clip hypertens ive (2K-1C) rats. However, heart ACE activity and mRNA increase with h ypertension. We measured the ACE activity and mRNA in hypertrophied he arts at different times after clipping, and determined the cellular di stribution of its increase in the left ventricle of 2K-1C hypertensive rats. Methods: Cardiac ACE activity was quantified in left and right ventricles using a radiolabeled synthetic ACE substrate, and ACE mRNA steady-state level was quantified by ribonuclease protection assay. Ti ssue localization of ACE in normal and hypertrophied hearts was determ ined by measuring ACE activity in isolated ventricular cells. In situ hybridization with a rat ACE cDNA and immunohistochemistry with a mono clonal anti-ACE antibody were used to identify tissue compartments pro ducing ACE mRNA and protein. Results: The left ventricle was hypertrop hied 2 weeks after clipping and remained hypertrophied at 12 weeks. Le ft ventricular ACE activity was significantly increased 2 and 4 weeks (3.2 +/- 0.3 in 2K-1C vs. 1.7 +/- 0.1 pmol/mg prot/min in sham-operate d rat) after renal artery clipping, but not at 12 weeks. The right ven tricle was slightly hypertrophied 4 weeks after clipping and remained hypertrophied at 12 weeks. Right ventricular ACE activity was signific antly increased at 4 (6.7 +/- 0.6 in 2K-1C vs. 3.1 +/- 0.3 pmol/mg pro t/min in sham-operated rat) and 12 weeks. ACE activity was not detecta ble in cardiomyocytes isolated by Percoll gradient. Neither was ACE mR NA detected in isolated cardiomyocytes, even after ACE mRNA amplificat ion by RT-PCR. In contrast, ACE activity and mRNA were detected in poo led non-cardiomyocytic cells. Thus the increase in cardiac ACE activit y associated with hypertension must be due to an increase in ACE expre ssion by non-cardiomyocytic cells. In situ hybridization showed an aut oradiographic signal for ACE mRNA over the endothelial cells of corona ry arteries and over the interstitial spaces including pericoronary an d fibrosis areas. Immunohistochemistry confirmed these data, showing A CE on endothelial cells and in pericoronary spaces with an increased s ignal in pericoronary and fibrosed areas in hypertensive hypertrophied left ventricle. Conclusion: Besides its usual endothelial expression, ACE is absent from cardiomyocytes and present in interstitial tissue, in the pericoronary spaces in normal tissue and more markedly in hype rtrophied ventricles.