FIBROUS TISSUE AND ANGIOTENSIN-II

Myofibroblasts (myoFb) are cells responsible for fibrous tissue format ion in injured systemic organs such as the heart. Cultured myoFb, obta ined from rat cardiac scar tissue, express genes that encode component s requisite for angiotensin (Ang) II generation, which in turn regulat es myoFb collagen turnover in an autocrine/paracrine manner, In this s tudy, we tested the hypothesis that these wound-healing fibroblast-lik e cells and locally generated Ang II are involved in other repairing t issue, To test this hypothesis, we used a granuloma pouch model, where a subcutaneous air sac is created followed by injection of croton oil . Pouch tissue was collected at days 4, 7, 14 and 21. The presence of myoFb was determined by immunohistochemical alpha-smooth muscle actin (alpha-SMA) labeling and collagen accumulation by picrosirius red stai ning. Angiotensin converting enzyme (ACE) and Ang II receptor binding were detected by in vitro, quantitative autoradiography using I-125-35 1A and I-125[Sar(1), Ile(8)]Ang II, respectively, while Ang II recepto r subtype was defined by displacement studies using either an AT(1) (l osartan) or AT(2) (PD123177) receptor antagonist. Cells expressing ACE were determined by immunohistochemistry. Ang II content in pouch tiss ue was measured by radioimmunoassay following HPLC separation while it s capacity to generate Ang II was assessed in tissue bath, with and wi thout exogenous Ang I or lisinopril. an ACE inhibitor. Collagen accumu lation in pouch tissue was examined by determining hydroxyproline cont ent in response to lisinopril, AT(1) or AT(2) receptor antagonists (lo sartan or PD123177). In pouch tissue. we found: (1) myoFb at day 4 whi ch became more extensive at days 7, 14 and 21; (2) morphologic evidenc e of collagen deposition evident at day 4, which gradually became more extensive thereafter; (3) ACE and Ang II receptor binding was evident at day 4 and remained invariant on days 7, 14 and 21; (4) the predomi nant Ang II receptor subtype expressed was AT(1): (5) myoFb express AC E and AT(1) receptors; (6) picogram quantities of Ang II (per g tissue ) was evident on days 7, 14 and 21: and (7) Ang II was generated from Ang I substrate. Lisinopril and losartan, but not PD123177, significan tly attenuated pouch weight and accumulation of collagen. Thus, in thi s model of cutaneous repair, the appearance of myoFb is associated wit h Ang II generation that regulates fibrogenesis by AT(1) receptor bind ing, Signals involved in the appearance of myoFb remain uncertain. Fur ther studies are required to address the regulation of Ang II generati on in pouch tissue of the rat. (C) 1997 Academic Press Limited.