AIM: To investigate how cholesterol (Ch) can affect thephenotype of bile duct fibroblasts of New Zealand rabbits.METHODS: 16 rabbits were divided randomly into twogroups: the control group and the experiment group. Therabbits in experiment group were fed with hypercholesteroldiet for 8 weeks. Bile duct was dissociated from rabbits andprepared for transmission electron microscopy. The purifiedbile duct fibroblasts were cultured and divided randomlyinto there groups: control group, Ch smiddle concentrationgroup (0.6 g/L), Ch high concentration group (1.2 g/L). Afterincubated for 72 h, the fibroblasts were made into specimensfor transmission electron microscopy. The expression of α-actin in bile duct fibroblasts was measured by means oflaser scanning confocal microscopy.RESULTS: With the transmission electron microscopy, thenormal bile duct fibroblasts were shuttle-shaped, and therewere abundant rough endoplasmic reticulums (RER), butfew mitochondria or microfilaments in cytoplasm. This isthe typical phenotype of fibroblasts. Bile duct fibroblasts ofhypercholesterolemic rabbits were observed, by thetransmission electron microscopy Rough endoplasmicreticulums were significantly reduced, with a lot ofmicrofilament bundles or stress fibers appeared in cytoplasm,especially under plasma membrane. Dense bodies werescattered within these bundles. Macula densas anddiscontinuous sarcolemma were found under plasmamembrane. It suggested that the bile duct fibroblasts ofhypercholesterolemic rabbits presented the phenotype ofsmooth muscle cell. The cultured bile duct fibroblasts alsohad typical phenotype of fibroblasts. After stimulated bymiddle concentration cholesterol (0.6 g/L) for 72 h, thereappeared lots of microfilaments in cytoplasm, but withoutdense body, macula densa and discontinuous sarcolemma.Observed with confocal microscopy, there were many regularbundles of microfilaments in fibroblasts treated with middleconcentration ch (0.6 g/L) and the expression of α-actinwas signifiantly increased. The average fluorescence valueof middle concentration group was 1 628+189 (P＜0.01 vscontrol group). Microfilaments and the expression of α-actinwere greatly decreased in fibroblastes of high concentrationgroup (1.2 g/L). The average fluorescence value of highconcentration group was 1 427±153 (P＜0.05 vs middleconcentration group). There were a lower expression of α-actin and few microfilaments in bile duct fibroblasts of controlgroup with an average fluorescence value of 1 224±138.CONCLUSION: Cholesterol can make bile duct fibroblastshave the phenotypic characteristics of smooth muscle cellboth in vitro andin vivo and this effect is more significant invivo. The effect is probably associated with some otherfactors besides cholesterol.