ANGIOTENSIN-II IS MITOGENIC IN NEONATAL RAT CARDIAC FIBROBLASTS

Angiotensin II has been reported to be a hormonal stimulus of cardiac growth, a response that may involve myocyte hypertrophy as well as gro wth of nonmyocytes. This study was designed to determine whether neona tal rat cardiac fibroblasts have an angiotensin II receptor that is co upled with hypertrophic and/or proliferative growth. Competitive radio ligand binding studies showed that cardiac fibroblasts have a single c lass of high-affinity (IC50, 1.0 nM) angiotensin II binding sites (B(m ax), 778 fmol/mg protein) that are sensitive to the competitive nonpep tide AT, receptor antagonist losartan (IC50, 13 nM). Other angiotensin peptides competed for [I-125]angiotensin II binding in the following rank order: angiotensin II>angiotensin III>angiotensin I> >[des-Asp1-d es-Arg2] angiotensin II. A nonhydrolyzable analogue of guanosine triph osphate increased the dissociation rate of bound [I-125]angiotensin II and decreased hormone binding to the receptor at equilibrium. The ang iotensin II receptor was coupled with increases in intracellular calci um. Incorporation of precursors into protein, DNA, and RNA in response to angiotensin II was determined. In serum-deprived cultures, a 24-ho ur exposure to 1 muM [Sar1]angiotensin II increased rates of phenylala nine, thymidine, and uridine incorporation by 58%, 103%, and 118%, res pectively. These increases were blocked by the noncompetitive AT, rece ptor antagonist EXP3174. After 48 hours, [Sar1]angiotensin II increase d total protein and DNA of cardiac fibroblasts by 23% and 15%, respect ively, with no change in the protein/DNA ratio. [Sar1]Angiotensin II i ncreased cell number by 138% after a 24-hour exposure, without affecti ng cell area. In summary, cardiac fibroblasts have G protein-linked AT , receptors that are coupled with proliferative growth. These results suggest that angiotensin II-induced cardiac hypertrophy is, in part, s econdary to stimulated increases in nonmyocyte cellular growth.