Angiotensin II type1 receptor regulation and differential trophic effects on rat cardiac myofibroblasts after acute myocardial infarction

Fibroblast growth in the scar and surviving tissue is a key element of the remodeling post myocardial infarction. The regulation of fibroblast growth after acute myocardial infarction remains to be determined. Recently, Angiotensin II has been demonstrated to be a mitogen for neonatal cardiac fibroblasts. In this study adult rat cardiac fibroblasts were isolated from different regions of the infarcted rat heart and Angiotensin II effects examined. Adult Wistar-rats were sham operated or left coronary artery ligated. After 4 days, hearts were removed and fibroblasts from sham operated, infarct- and non-infarct regions of the left ventricle isolated. Radioligand binding studies were performed and cell number, cell area, total protein, and AT(1) receptor mRNA after stimulation determined. Radioligand binding studies demonstrated that myofibroblasts expressed a single class of high affinity Angiotensin II AT(1) receptors. Myofibroblasts from the infarct area revealed a lower maximal binding capacity, compared to sham operated myocardium. Conversely, myofibroblasts from the non-infarct area had a higher expression of Angiotensin II AT(1) receptor mRNA compared to sham operated myofibroblasts. Angiotensin II (1 microM, 48 h) increased cell-number in sham operated and non-infarct, but not in infarct myofibroblasts. Angiotensin II elevated total protein in sham operated, non-infarct, and infarct myofibroblasts. In addition, Angiotensin II increased cell area in sham operated and infarct myofibroblasts. These data demonstrate that Angiotensin II acted as a mitogen in sham operated and non-infarct myofibroblasts and stimulated hypertrophy in infarct myofibroblasts. These regional different effects of Angiotensin II might participate in the remodeling post myocardial infarction.