长期胰岛素治疗通过促进BNP表达延缓缺血性心力衰竭的发展及其机制

Long-term insulin treatment improves postischemic cardiac structure and function via increasing serum BNP levels

目的:探讨心肌梗死后长期胰岛素治疗对心脏结构与功能的影响及机制。方法:对成年雄性SD大鼠行冠状动脉左前降支结扎手术,并随机分为4组(每组8～10只):(1)生理盐水组:心梗后1 mL·kg-1·d-1,ih,4周;(2)胰岛素组:2 U·kg-1·d-1,ih,4周;(3)胰岛素+wortmannin(Wm,PI3K抑制剂)组:Wm 15μg·kg-1·d-1,胰岛素给药前15 min,ip;(4)假手术组不结扎冠脉,作为对照。检测各组大鼠心脏结构及功能,测定心肌细胞PI3K及p38 MAPK表达量,测定血清脑钠尿肽(BNP)及心肌BNP mRNA表达量。结果:心梗后胰岛素长期强化治疗4周可减少心脏纵轴长度/心脏重量,但对心脏重量/体重和心肌细胞横截面积无显著影响,并增加心脏射血分数、左心室发展压和左室压微分(均P<0.05);此外,胰岛素治疗4周可增加PI3K表达和Akt磷酸化,降低p38 MAPK磷酸化水平,同时提高血清BNP水平而不改变心肌细胞BNP mRNA表达量,但该作用不能被Wm阻断(均P<0.05)。结论:心梗后长期胰岛素强化治疗可通过非PI3K-Akt依赖通路上调BNP水平,减轻心脏病理性重构并改善心功能,延缓缺血性心力衰竭的发展。

AIM：To investigate the influence of long-term insulin treatment on postischemic cardiac structural and functional changes, and to further explore the underlying mechanisms. METHODS：Adult male SD rats were randomly divided into 4 groups （8-10 rats per group）： sham group, myocardial infarction （MI） ＋ saline （1 mL·kg^-1·d^-1hypodermic injection for 4 weeks） group, MI ＋ insulin （2 U·kg-1·d-1, hypodermic injection for 4 weeks） group and MI ＋ insulin （2 U·kg-1·d-1, hypodermic injection for 4 weeks） ＋ wortmannin [a phosphatidylinositol 3-kinase （PI3K） inhibitor; 15 μg·kg-1·d-1, intraperitoneal injection 15 min before each insulin treatment] group. The rats in the latter 3 groups were subject to ligation of the left anterior descending coronary artery, while those in sham group underwent the same surgical procedures without tying the sutures. The cardiac structural and functional changes were observed by echocardiogram, heart catheterization and microscopy with HE and Masson trichrome staining. Blood glucose was determined by Roche blood glucose meter, and the serum levels of insulin and brain natriuretic peptide （BNP） were detected by ELISA. The protein expression and phosphorylation of PI3K, Akt, glycogen synthase kinase 3β （GSK3β） and p38 mitogen-activated protein kinase （p38 MAPK） in myocardial tissues were detected by Western blotting. The mRNA expression of BNP, β-myosin heavy chain （β-MHC） and atrial natriuretic peptide （ANP） in myocardial tissues was determined by real-time fluorescence quantitative PCR. RESULTS：At the end of the 4th week, MI rats receiving long-term insulin treatment showed decreased ratio of heart length/heart weight, smaller systolic left ventricle cavity, thicker systolic interventricular septum, and increased cardiac ejection fraction, left ventricular development pressure and instantaneous first derivate of left ventricle pressure （P〈0.05 vs MI ＋ saline group）. Moreover, insulin treatment significantly increased the phosphorylation of PI3K and Akt and the serum level of BNP, and inhibited the phosphorylation of p38 MAPK （P〈0.05 vs MI ＋ saline group）, but did not change the mRNA expression of BNP in myocardial tissues. The effects of insulin on BNP were not blocked by wortmannin （P〉0.05 vs MI ＋ insulin group）. CONCLUSION：Insulin improves postischemic cardiac structure and function by increasing serum BNP levels possibly independent of PI3K-Akt signaling pathway.