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 adrenomedullin (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 assessed by [3H]thymidine and [3H]phenylalanine incorporation, respectively.


RESULTS
Cultured cardiac fibroblasts secreted AM into the medium time-dependently at a rate of 20.3 +/- 3.0 fmol/5 x 10(4) cells/48 h, mean +/- S.D. Northern blot analysis showed expression of preproAM mRNA of 1.6 kb in these cells. 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 ET-1-stimulated [3H]thymidine and [3H]phenylalanine incorporation in a dose-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 AM effects, inhibiting the Ang II-stimulated [3H]thymidine and [3H]phenylalanine incorporation. Blockage of the effect of endogenous AM by anti-AM monoclonal antibody not only significantly reduced the basal level of intracellular cAMP, but also enhanced the [3H]thymidine and [3H]phenylalanine incorporation into the cells.


CONCLUSIONS
Cultured neonatal rat cardiac fibroblasts produce and secrete AM, and the secreted AM may inhibit proliferation and protein synthesis of these cells. AM may exert these inhibitory effects partly by elevating intracellular cAMP. It is suggested that AM has an important role in modulating the growth of cardiac fibroblasts in an autocrine or a paracrine manner.
Tsuruda
T
T
First Department of Internal Medicine, Miyazaki Medical College, Japan.
Kato
J
J
Kitamura
K
K
Kawamoto
M
M
Kuwasako
K
K
Imamura
T
T
Koiwaya
Y
Y
Tsuji
T
T
Kangawa
K
K
Eto
T
T
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D053607:Adrenomedullin; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D019898:Autocrine Communication; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D019332:Endothelin-1 / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008916:Miotics / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D019899:Paracrine Communication; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000276:immunology / Q000494:pharmacology / Q000502:physiology*; D014176:Protein Biosynthesis; D051381:Rats; D017208:Rats, Wistar
D000911:Antibodies, Monoclonal; D019332:Endothelin-1; D008916:Miotics; D010446:Peptide Fragments; D010455:Peptides; D000804:Angiotensin II; C058636:calcitonin gene-related peptide (8-37); D053607:Adrenomedullin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D004247:DNA; D000242:Cyclic AMP; D015740:Calcitonin Gene-Related Peptide