Role Of Bradykinin In Angiotensin-(1-7) Inhibition Of Proliferation Of Cardiac Fibroblasts

Objective To explore the role and possible mechanisms of action of bradykinin (BK) in angiotensin-(1-7) [Ang-(1-7)] inhibition of the proliferation and the collagen synthesis of cultured cardiac fibroblasts induced by angiotensin II (AngII).Methods Neonatal rat cardiac fibroblasts were divided into 5 groups: control, Angll, Ang-(1-7), AngII+Ang-(1-7), and AngII+Ang-(l-7)+HOE-140. Fibroblast proliferation was assessed by MTT assay , collagen synthsis by hydroxyproline assay, production of nitric oxide (NO) by the nitric acid reductase method, and production of cGMP by radiommunoassay.Results (1) After incubating the fibroblasts with 10^-7 M Angll for 36 hours, fibroblasts number and collagen synthesis was significantly increased comparing with control [100% vs. (51.8 ± 1.8)% , 100%vs. (62.2 ±3.1)% P< 0.01 ], indicating that Angll stimulated fibroblasts proliferation and increased collagen synthesis . (2) 10^-6 M Ang-(1-7) inhibited AngII-induced fibroblasts proliferation in a dose-dependent manner, lowering the number of fibroblasts and collagen to (57.9 ± 2.1)% and (72.1 ±2.3) % respectively (P < 0.01). (3) NO and intracellular cGMP were significantly lower in the Ang II group comparing with control (P < 0.01). However 10^-6 M Ang-(1-7) significantly increased NO and intracellular cGMP to (177.2 ± 6.9 )%, (242.3 ±19.1) %, respectively, comparing with AngII (P < 0.01). (4) The BK subtype 2 receptor antagonist HOE-140 attenuated Ang-(1-7) inhibition of Ang II-induced fibroblasts proliferation and increased collagen synthesis, and also blunted the increase in NO and cGMP in response to Ang-(1-7). [ (88.9 ± 4.2)% vs. (57.9 ± 2.1)% , (87.8± 1.2)% vs. (72.1 ±2.3) %, (125.7 ±8.2)% vs. (177.2 ±6.9)%, (162.2 ±14.7 )% vs. (242.3 ± 19.1) %, respectively, P < 0.01 ].Conclusion The interaction between Ang-(1-7) and BK, resulting in increased production of NO and cGMP, might be involved in the process which Ang-(l-7) inhibitsthe proliferation and the collagen synthesis of cultured cardiac fibroblasts induced by Angll.