IN-SITU PRODUCTION OF ANGIOTENSIN-II BY FIBROSED RAT PERICARDIUM

Following pericardiotomy in rats, subsequent fibrosis of the visceral pericardium becomes a site of high-density angiotensin-converting enzy me (ACE) binding. This study was undertaken to determine whether this exteriorized site of ACE activity is associated with angiotensin II (A ngII) production. Four weeks after pericardiotomy, hearts were isolate d and maintained by Krebs-Henseleit perfusion; coronary venous and The besian drainage were removed by cannulae. Following a 30-min period of stabilization, a balloon containing superfusate was placed around the heart. Superfusate composition was controlled and included either lis inopril (10(-7) mol/l), angiotensin I (AngI, 10(-7) mol/l), or angiote nsinogen (10(-6) mol/l). Sixty min later, superfusate AngII concentrat ion was determined (high-performance liquid chromatography followed by radioimmunoassay). Pericardial fibrosis was confirmed by picrosirius red staining and its high-density ACE binding by quantitative in vitro autoradiography (I-125-351A). ACE activity was measured by hippuryl-h istidyl-leucine degradation. In coronary effluent, AngII concentration and ACE activity were not different between controls and hearts with pericardial fibrosis. Compared to unoperated, age/sex-matched control hearts, however, we found those with pericardial fibrosis to have: (a) significantly (P<0.05) greater tissue ACE activity (118.42 +/- 6.66 v 89.45 +/- 7.70 nmol/min/g); (b) significantly (P<0.01) greater superf usate AngII concentration (4.98 +/- 0.94 v 1.43 +/- 0.28 pg/ml); (c) l isinopril markedly attenuated superfusate AngII concentration to that seen in controls; (d) exogenous AngI markedly increased AngII producti on (13.76 +/- 1.65 v 4.98 +/- 0.94 pg/ml); and (e) exogenous angiotens inogen did not alter superfusate AngII. Thus, high-density ACE binding and ACE activity of fibrosed pericardium is responsible for AngII pro duction in this in vitro model. Cells involved in generating AngI at t his site are uncertain and may involve fibroblast-like cells that expr ess ACE and have ACE activity. The role of local AngII production is u nknown, but its autocrine/paracrine properties may regulate collagen t urnover of these cells. (C) 1996 Academic Press Limited