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Angiotensin II (Ang II), a potent mediator of vascular remodeling, can stimulate the synthesis of extracellular matrix in vascular cells. Recent studies indicate that connective tissue growth factor (CTGF) is involved in collagen synthesis. There is also increasing evidence that adventitial fibroblasts (AFs) are actively involved in vascular remodeling. However, whether collagen synthesis by AFs is mediated by CTGF, or whether it is relevant to Ang II, has not been studied. The present study was conducted to determine whether CTGF is expressed in AFs, and if so, whether the CTGF produced by AFs participates in collagen synthesis. The AFs were isolated from thoracic aorta of Wistar-Kyoto rats (WKY). The expression of CTGF was measured by Western blot or real-time PCR. Collagen synthesis was assessed by [(3)H]proline incorporation. Our results suggested that CTGF was expressed in AFs and secreted into medium. Ang II increased CTGF mRNA and protein expression in a time- and dose-dependent manner, with the maximal protein increase occurring at 24 h with an Ang II dose of 10(-7) mol/L, and this increase was inhibited by the Ang II receptor type 1 (AT(1)-R) antagonist losartan, but not by the Ang II receptor type 2 (AT(2)-R) antagonist PD123319. Ang II dose-dependently stimulated the incorporation of [(3)H]proline into cultured AFs, and this effect was inhibited by a CTGF antisense oligodeoxynucleotide. Overexpression of CTGF by pcDNA3.1(+)/CTGF increased [(3)H]proline incorporation in cultured AFs. The results demonstrated that, in cultured AFs, Ang II increased CTGF production via AT(1)-R, which could be mediators of collagen synthesis by Ang II. This finding suggests that CTGF might be a novel target for antifibrotic therapy in vascular diseases.