Aim The purpose of the study is to evaluate the role of AT-1 anti-sense nucleotide (AT-1A) in expression of subtypes of angiotensin Ⅱ(AngⅡ) receptor mRNA, and syntheses of protein and nucleic acid in cultured rat adventitial fibroblasts. Methods AT-1 cDNA sequence (476 bp) was cloned with RT-PCR and inserted into PLXSN reversely to construct an intact plasmid containing AT-1A(PAT-1A). It was transfected into cultured rat adventitial fibroblasts,and identified by RT-PCR and Western blot. Syntheses of protein and nucleic acid by 3 H-Leu and 3 H-TdR incorporation, mRNA expressions of AT-1 and AT-2 by RT-PCR, were compared between transfected and nontransfected cultured rat adventitial fibroblasts after being stimulated for 24 h by AngⅡ 10 -7 mol/L. Results AT-1 mRNA and protein were expressed significantly less in cultured rat adventitial fibroblasts than that in control (P<0.01). AT-1 mRNA expression was markedly decreased,and AT-2 mRNA obviously increased (P<0.01); but no apparent difference was found in 3 H-Leu and 3 H-TdR incorporation between transfected and nontransfected cultured rat adventitial fibroblasts after stimulation for 24h of AngⅡ10 -7 mol/L (P>0.05). Conclusion After being blocked by AT1A, expression of AT-1 mRNA in cultured rat adventitial fibroblasts was markedly suppressed,while AT-2 mRNA up-regulated at the same time. It is shown that both syntheses of protein and nucleic acid in cultured rat adventitial fibroblasts mediated by AngⅡ could not be effectively interrupted simply by AT-1A blocking.