ObjectiveWe have demonstrated that cultured vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR), but not from normotensive Wistar-Kyoto (WKY) rats, produce angiotensin II (Ang II) in a homogeneous culture with increased levels of angiotensinogen, cathepsin D and angiotensin converting enzyme (ACE) at early passages. In the current study, we investigated how changes in the cell phenotype affect the Ang II-generating system and the growth of VSMC from SHR.Design and methodsWe evaluated basal DNA synthesis by [3H]thymidine incorporation, immunofluorescence of α-smooth muscle (SM) actin, mRNA expression of phenotype markers such as SM22α appeared by contractile phenotype, Ang II-generating system components and growth factors by reverse transcription and polymerase chain reaction analysis, and Ang II levels by radioimmunoassay in quiescent VSMC from WKY/Izumo rats and SHR/Izumo at passages 4, 8 and 12.ResultsBasal DNA synthesis in VSMC from WKY rats increased with increasing passage number, whereas in cells from SHR it was markedly higher at early passages and was not affected by the passages. At early passage numbers, immunofluorescence of α-SM actin was stronger in VSMC from WKY rats than in cells from SHR, but decreased after several passages. Expression of SM22α mRNA was higher in VSMC from WKY rats than in cells from SHR at early passages, and decreased after several passages in cells from both rat strains. Expression of matrix Gla mRNA was higher in VSMC from SHR than in cells from WKY rats at early passage, and increased after several passages in cells from both rat strains. Ang II was not detected at early passages but increased in VSMC from WKY rats with increasing passage, whereas it was detected in VSMC from SHR at early passages and did not change with the passages. Expression of angiotensinogen mRNA was higher in VSMC from SHR than in cells from WKY rats, and was not affected by the passages. Expressions of cathepsin D and ACE mRNA were higher in VSMC from SHR than in cells from WKY rats at early passage, and were increased by the passages in VSMC from WKY rats. Expressions of transforming growth factor-β1, platelet-derived growth factor A-chain, and basic fibroblast growth factor mRNA were significantly higher in VSMC from SHR than in cells from WKY rats, and were increased by the passages.ConclusionThese data indicate that early in culture VSMC from SHR have the synthetic phenotype, whereas VSMC from WKY rats have the contractile phenotype which then changes to the synthetic phenotype after increased passage numbers, with increased expression of cathepsin D and ACE, which produce Ang II, and increased expression of Ang II-related growth factors, which induce the exaggerated growth observed in VSMC from SHR.