NG-硝基-L-精氨酸甲基酯对心力衰竭大鼠应用β3受体激动剂后血流动力学和β受体mRNA表达水平的影响

目的研究不同剂量NG-硝基-L-精氨酸甲基酯(L-NAME)作用于心力衰竭(心衰)大鼠应用β3受体激动剂BRL37344(BRL)后的血流动力学、环-磷酸鸟苷(cGMP)含量和β受体mRNA表达水平,进一步明确β3受体在心衰中的作用途径和L-NAME的作用特点.方法将大鼠随机分为对照组(Ⅰ组)、异丙肾上腺素(Iso)组(Ⅱ组)、Iso+BRL组(Ⅲ组)、Iso+BRL+L-NAME低剂量组(5 mg/kg体重,Ⅳ组)、Iso+BRL+L-NAME中剂量组(50 mg/kg体重,Ⅴ组)、Iso+BRL+L-NAME高剂量组(100 mg/kg体重,Ⅵ组).测定 (1)血流动力学 左室舒张末压(LVEDP),左室收缩末压(LVESP),左室压力最大上升、下降速率(±dp/dt).(2)心肌cGMP含量.(3)心肌组织β1、β2、β3受体mRNA水平.结果①Ⅱ组较Ⅰ组±dp/dt绝对值、LVESP明显降低,LVEDP明显升高(除-dp/dt P< 0.05,余均为P< 0.01);Ⅲ组较Ⅱ组-dp/dt绝对值、LVESP明显下降,LVEDP明显升高(P< 0.05),+dp/dt变化呈下降趋势,但差异无统计学意义;随着L-NAME剂量的增加,±dp/dt绝对值升高,LVEDP降低,但大剂量L-NAME应用后,血流动力学又有恶化倾向. ②Ⅰ、Ⅱ、Ⅲ组cGMP水平呈逐渐上升趋势(均为P< 0.01),应用L-NAME后随着剂量的增加Ⅳ、Ⅴ、Ⅵ组cGMP呈下降趋势,大剂量应用L-NAME后cGMP回到正常对照组水平.③Ⅰ、Ⅱ、Ⅲ组比较,β1受体mRNA/β-actin mRNA为Ⅰ组最高、Ⅲ组最低,差异有统计学意义(均为P<0.01);β2受体mRNA/β-actin mRNA呈下降趋势,但三组间差异无统计学意义;而β3受体mRNA/β-actin mRNA的三组中Ⅲ组最高、Ⅰ组最低,差异有统计学意义(均为P<0.01);而Ⅳ、Ⅴ、Ⅵ组三种β受体mRNA水平与Ⅲ组相似,差异无统计学意义.结论β3受体经NOS途径发挥作用,L-NAME可部分阻断β3受体激动剂对衰竭心脏的负性肌力作用,改善心功能,但大剂量应用会加重心衰进程.

Effects of NG-nitro-L-arginine methyl ester on hemodynamics and beta-adrenoreceptors mRNA in rats with heart failure after beta3-adrenergic receptors agonist injection

OBJECTIVE: To evaluate the effects of different doses of N(G)-nitro-L-arginine methyl ester (L-NAME) on hemodynamics, cyclic guanosine monophosphate (cGMP) production and the level of beta-adrenergic receptors (beta-ARs) mRNA in a heart failure rat model after BRL-37344 (beta(3)-ARs agonist) injection. Meanwhile, to investigate the influence of beta(3)-ARs and L-NAME on signal transduction in failing heart. METHODS: The rats were randomly divided into six groups, control group (group I), Iso (isoproterenol) group (group II), Iso + BRL group (group III), Iso + BRL + low dose of L-NAME group (5 mg/kg, group IV), Iso + BRL + moderate dose of L-NAME group (50 mg/kg, group V), Iso + BRL + high dose of L-NAME group (100 mg/kg, group VI). The hemodynamics [left ventricular end systolic pressure (LVESP), +/- dp/dt, left ventricular end diastolic pressure (LVEDP)], cardiac cGMP and the levels of beta(1)-, beta(2)-, and beta(3)-ARs mRNA were measured. RESULTS: (1) LVESP, +/- dp/dt values in group II were significantly lower, and LVEDP was significantly higher than that in group I (except -dp/dt P < 0.05, the rest were P < 0.01). Comparing with group II, group III had lower -dp/dt value and LVESP, higher LVEDP (P < 0.05). The level of +dp/dt had a trend to be lower but lacked statistical significance between two groups. The value of +/- dp/dt got higher and LVEDP got lower along with higher dose of L-NAME, but a large dose of L-NAME had more deteriorated cardiac functions. (2) The cardiac cGMP in group I, II and III had a higher tendency (P < 0.01). The tendency of cardiac cGMP in group IV, V and VI was inversed with the dose of L-NAME. After a large dose of L-NAME was applied, cGMP returned to the same level as Group I. (3) Among groups I, II and III, the level of beta(1)-AR mRNA was the highest in group I and the lowest in group III (P < 0.01). The levels of beta(2)-AR mRNA were also tended to be lower among three groups but with no significance. While the level of beta(3)-AR mRNA was the highest in group III. The levels of beta-AR mRNA were all the same in group VI, V and VI. CONCLUSIONS: The negative inotropic effect of beta(3)-ARs stimulation was mediated by activation of the NOS pathway. L-NAME blocked beta(3)-ARs agonist negative chronotropic effect on failing heart partly and improved hemodynamics, but a large dose of L-NAME had more deteriorated cardiac functions.