Remodeling of large and small arteries contributes to the development and complications of hypertension. Artery structural changes in chronic sustained hypertension include vascular smooth muscle cells (VSMC) proliferation and extracellular matrix (ECM) modifications. Extracellular constituents such as proteoglycans (PGs), may modulate vascular stiffness and VSMC growth and differentiation. We examined the effect of growth factors on secreted and membrane-bound PGs synthesis by cultured aortic smooth muscle cells (SMC) from 12- to 14- week-old spontaneously hypertensive rats (SHR) and age-matched Wistar rats. After stimulation with platelet-derived growth factor (PDGF-BB), 10% fetal calf serum (FCS) or 0.1% FCS as control, PGs synthesis (dpm/ng DNA) was evaluated in the medium (M-ECM) and in the cell layer (P-ECM) by a double-isotopic label method using both [3H]-glucosamine and [35S]-sodium sulfate which are incorporated into all complex carbohydrates or only into sulfated dysaccharides, respectively. Data are presented as percent of the control (0.1% FCS). SHR VSMC displayed a significantly greater synthesis of M-ECM [3H]-PGs than Wistar rat cells, with both treatments, but no differences in M-ECM [35S] uptake were found in any case. In the P-ECM, both PDGF-BB and 10% FCS produced a greater effect on [3H]-PGs and sulfated PGs synthesis in VSMC from SHR. An important change seen in SHR cells was a significant decreased sulfation, assessed by [35S]/[3H] ratio, in basal and stimulation conditions. Present results indicate the existence of changes in PGS synthesis and modulation in VSMC from a conduit-artery of SHR and support the pathophysiological role proposed for matrix proteoglycans in the vascular wall changes associated to hypertension and related vascular diseases as atherosclerosis.