ObjectiveTo evaluate effects of eicosapentaenoic acid (EPA), an n–3 polyunsaturated fatty acid, on the exaggerated growth of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR).DesignCultured VSMC were prepared by an explant method from thoracic aortas in 8-week-old male Wistar–Kyoto (WKY)/Izumo rats and SHR/Izumo. Effects of EPA on basal DNA synthesis, expression of growth factors and cyclin-dependent kinase 2 (cdk2) activity were examined in VSMC from WKY rats and SHR.MethodsThe cell cycles were synchronized with serum deprivation, then DNA synthesis in VSMC was measured by [3H]-thymidine incorporation. Fatty acid composition of the phospholipid fraction in VSMC was measured by gas chromatography. Expression of platelet-derived growth factor (PDGF) A-chain, transforming growth factor (TGF)- β1 and basic fibroblast growth factor (bFGF) mRNAs was evaluated by reverse-transcription and polymerase chain reaction analysis. Cdk2 activity was determined by autoradiography after polyacrylamide gel electrophoresis of VSMC extracts that had been immunoprecipitated with anti-cdk2 antibody and protein A sepharose, and then incubated with32P-ATP and histone H1.ResultsHigh concentrations (40 and 80 μmol/l) of EPA significantly inhibited basal DNA synthesis in VSMC from both rat strains. Low dose (20 μmol/l) of EPA significantly inhibited basal DNA synthesis in VSMC from SHR, whereas the same dose of EPA stimulated DNA synthesis in VSMC from WKY rats. In analysis of fatty acid composition, low dose of EPA was considerably incorporated in VSMC. Low dose of EPA significantly inhibited angiotensin II- and phorbol ester milisterol-stimulated DNA synthesis in VSMC from both rat strains, whereas EPA did not affect PDGF-AA-stimulated DNA synthesis in VSMC from either rat strain. Low dose of other polyunsaturated fatty acids such as docosahexaenoic acid, arachidonic acid and linoleic acid did not significantly affect basal DNA synthesis in VSMC from either strain. Low dose of EPA significantly inhibited expression of TGF-β1 mRNA in VSMC from SHR, whereas EPA did not affect expression of PDGF A-chain and bFGF mRNAs in VSMC from SHR. Cdk2 activity in VSMC from SHR was higher than that from WKY rats. Low dose of EPA inhibited cdk2 activity in VSMC from SHR, whereas it stimulated the activity in VSMC from WKY rats.ConclusionLow dose of EPA exerted specific inhibition of the exaggerated growth of VSMC from SHR through the suppression of TGF-β.