Abstract: Objective To probe the change of myocardial cells and collagen I/III protein expression of the left ventricular induced by isoprenaline hydrochloride (ISO) in rats. Methods Adult rats were treated with intraperitoneal injection of ISO by 4mg/(kgI>&#/I>8226;d) for 1, 4 and 8 weeks to prepare SD rats model of myocardial ischemia. The control group were treated with the same volume of the physiologic saline. The tissue structure of the left ventricular was observed with the electron and light microscopes. The expression of collagen I/III protein was detected with immunohistochemistry and Western blotting. The expressive intension and the area percentage were statistically treated with the HAPIS-2000 image analysis system and SPSS10.0 software. Results Under the light microscope, the necrotic area of myocardial ischemia appeared near the endocardium when induced by ISO. In the necrotic area of ischemia collagen I/III was of high expression, and the percentage of the necrotic area was of the decreasing tendency.The difference between groups of 1 week and 4 weeks was of no statistical significance( EM>P /EM>>0.05), and the difference between the groups of 4 weeks and 8 weeks was of statistical significance ( EM>P/EM> <0.05). The difference of the expression intensity when compared among groups was of no statistical significance( EM>P/EM> >0.05). The early period of myocardial cells in the non-necrotic area of ischemia was the mass collection of glycogenosome, and the characteristic of the later period was the increase of the mitochondria and the loose myofibrilla. There was no obvious change in the area percentage of collagen I protein when detected with immunochemistry, and the difference among groups was of no statistical difference (EM> P/EM> >0.05). The difference of the expression intensity when compared among the experimental groups was of no statistical significance ( EM>P /EM>>0.05), but compared with the control group, the expression intensity decreased and the difference was of statistical difference ( P <0.05). The area percentage of collagen III protein was of the increasing tendency when detected with immunochemistry, and the difference between the groups of 1 week and 4 weeks was of statistical significance ( EM>P/EM> <0.05). The expression intensity was stable and the difference among groups was of no statistical significance ( P <0.05). The result of Western blotting showed that the collagen I/III protein among the experimental groups was of a tendency from increasing to decreasing, and the difference among the groups was of statistical significance ( EM>P /EM><0.05). Conclusion Long-time inducement may lead to the ischemic necrosis of the myocardial cells near the endocardium. The necrotic area of ischemia is generally of a decreasing tendency and fibrous change appears in this area, which is associated with the increase of stiffness of the left ventricular wall. The hypertrophy of the myocardial cells in the nonnecrotic area of ischemiais associated with the energy metabolism. Collagen I/III protein does not involve in the stiffness and the compliance of left ventr

Key words: Isoprenaline hydrochloride, Myocardial hypertrophy, Collagen I/III, Immunohistochemistry, Western blotting, Rat