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It was widely believed that over-activation of sympathetic system contributed to the process of heart failure, so that over-dose treatment of isoproterenol (ISO) was widely used to mimic heart failure in mice. However, a lot of data showed that the process and severity of heart failure depended on the dose, period and drug delivery way of ISO. A standard protocol and optimal time window is desperately needed, especially for pharmacological research. In this study, we will use isoproterenol to induce heart failure in mice, and then investigate its dynamic pathophysiological features. Thus, we will tell the optimal time window for pharmacological researches of drugs which focused on different stage of heart failure.
Healthy male C57BL/6 mice (20g±1g) were divided into 2 groups, including a model group and a control group. Heart failure was induced by subcutaneous injection of gradient ISO (20mg/kg for the first day; 10mg/kg for the second day, 5mg/kg per day from the third day to the fourteenth day) in mice of model group, while normal saline was used in control mice. The changes of cardiac structure and function were evaluated by echocardiography, and then the pathological lesions of heart tissue were observed by measuring organ indexes and preparing Hematoxylin-Eosin staining of heart section. To get the dynamic data of this model, all evaluations were performed at the end of 2, 4, 6, 8, 12 weeks.
1. More than 35% decrease of ejection fraction (EF) was observed at the end of 2 weeks (model vs. control, 48.00±9.91 vs. 72.16±11.48, %, P<0.01). At the end of 6 weeks, EF decreased to 39.6%, and then kept being around 40% until the end of 12 weeks.
2. Fractional shortening was decreased significantly at the end of 2 weeks (model vs. control, 23.17±5.92 vs. 39.03±10.48, P<0.01) and showed a similar pattern with EF.
3. Significant increase of left ventricular internal systolic diameter (LVIDs) was observed at the end of 2 weeks (P<0.01). This kind of changes was similar until the end of 12 weeks (P<0.01). LVIDs has a slight increase from 2 to 12 weeks.
4. The heart index (heart mass/ tibial length) was increased significantly at the end of 2 weeks when comparing to the control group (model vs. control, 7.32±0.67 vs. 6.44±0.33, mg/cm, P<0.05). The heart index was stable from 2 weeks to 4 weeks, and then it showed slight increase until 12 weeks.
5. Significant increase of lung index (lung mass/ tibial length) was present from the end of 4 weeks (P<0.05), while dramatic changes of liver index (liver mass/ tibial length) appeared at the end of 4 weeks (P<0.05).
6. Increased deposition of collagen was observed in the heart section of model mice at the end of 2 weeks, and lesions kept aggravating during the entire experiment.
Heart failure was successfully induced by ISO in mice by following the protocol we established. Deficiency of left ventricular systolic function was observed at the end of 2 weeks. When injection of ISO was stopped, the process of heart failure was relative slow in the following 2 weeks. And then the heart function of model animals deteriorate quickly in the next 2 weeks. As a result, left heart failure was changed to whole heart failure at the end of 6 weeks. From 6 to 12 weeks, model mice were kept in the similar stage. Thus, this heart failure model mimicked different stages of heart failure and was an optimal model for pharmacological research.