An autocrine or a paracrine role of adrenomedullin in modulating cardiac fibroblast growth

Objective: The aim of the present study was to determine the role of adreno medullin (AM) in cardiac fibroblasts. Methods: The production and secretion of AM were examined in cultured neonatal rat cardiac fibroblasts, and the effects of AM on proliferation and protein synthesis of these cells were as sessed by [H-3]thymidine and [H-3]phenylalanine incorporation, respectively . Results: Cultured cardiac fibroblasts secreted AM into the medium time-de pendently at a rate of 20.3+/-3.0 fmol/5x10(4) cells/48 h, mean+/-S.D. Nort hern blot analysis showed expression of preproAM mRNA of 1.6 kb in these ce lls. In addition, 10(-6) mol/l of angiotensin II (Ang II) and endothelin-1 (ET-1) significantly increased the AM secretion by 55 and 48%, respectively . Synthetic AM significantly reduced 10(-6) mol/l Ang II- or 10(-7) mol/l E T-1-stimulated [H-3]thymidine and [H-3]phenylalanine incorporation in a dos e-dependent manner, and these effects were attenuated by a calcitonin gene- related peptide (CGRP) type 1 receptor antagonist, CGRP(8-37). Synthetic AM also had a dose-dependent stimulatory effect on cAMP accumulation in these cells, which was significantly attenuated by CGRP(8-37). A cAMP analogue, 8-bromo-cAMP, mimicked the ARI effects, inhibiting the Ang II-stimulated [H -3]thymidine and [H-3]phenylalanine incorporation. Blockage of the effect o f endogenous AM by anti-AM monoclonal antibody not only significantly reduc ed the basal level of intracellular cAMP, but also enhanced the [H-3]thymid ine and [H-3]phenylalanine incorporation into the cells. Conclusions: Cultu red neonatal rat cardiac fibroblasts produce and secrete AM, and the secret ed AM may inhibit proliferation and protein synthesis of these cells. AM ma y exert these inhibitory effects partly by elevating intracellular cAMP. It is suggested that AM has an important role in modulating the growth of car diac fibroblasts in an autocrine or a paracrine manner. (C) 1999 Elsevier S cience B.V. All rights reserved.