CONTROL OF METABOLISM BY NO IN THE FAILING HEART

一氧化氮在控制心脏代谢中的作用正得到越来越多研究的支持。我们最近发现，正常狗的NO合成酶（NOS）的急性阻断和起搏引起的心力衰竭期间NO产量的下降都与心脏从游离脂肪酸（FFA）到碳水化合物利用的转换有关。这些现象背后的机制尚不清楚。本研究计划将确定NO在控制心脏底物利用中的作用，以及这种作用是否在心力衰竭期间丧失。第一个具体目的是确定NO是否控制心脏FFA和碳水化合物代谢。通过注入同位素标记的游离脂肪酸、葡萄糖和乳酸，测量清醒犬在NOS阻断前后心脏中游离脂肪酸和碳水化合物氧化的速率。标记的底物积累和碳水化合物和游离脂肪酸氧化的关键酶的活性将在体内实验结束时在冷冻夹住的心脏活检中进行测量。组织的快速冷冻将使酶的激活状态从体内一直保持到体外。第二个具体目的是确定心力衰竭期间心肌代谢和生化变化是否与正常心脏NOS阻断后的心肌代谢和生化变化相似，以及是否可以通过no释放剂逆转。在体内和体外将采用相同的方法。长期起搏会引起狗的心力衰竭。第三个具体目的是确定动脉底物浓度的急性改变是否会影响心力衰竭期间的心脏耗氧量，以及这种影响是否可以通过no释放剂逆转。我们的初步数据表明，FFA消耗可以引起心脏O2消耗的增加，与血流动力学变化无关，但仅在NO缺失的情况下。这些研究将阐明一氧化氮在心衰病理生理中的作用。这也将为no -供体治疗心力衰竭提供新的药理机制。基于这些药物直接控制心脏代谢。

A role for NO in the control of cardiac metabolism is receiving support from an increasing number of studies. We recently found that the acute blockade of NO synthase (NOS) in normal dogs and the fall in NO production during pacing induced heart failure are both associated with a switch from free fatty acids (FFA) to carbohydrate utilization by the heart. The mechanisms underlying these phenomena are unknown. This research proposal will determine the role of NO in the control of cardiac substrate utilization and whether this role is lost during heart failure. The first specific aim is to determine whether NO controls cardiac FFA and carbohydrate metabolism. The rate of FFA and carbohydrate oxidation in the heart, before and after NOS blockade, will be measured in conscious dogs by infusing isotope-labeled FFA, glucose and lactate. Labeled substrate accumulation and the activity of key enzymes for carbohydrate and FFA oxidation will be measured in cardiac biopsies freeze-clamped at the end of the in vivo experiment. The rapid freezing of the tissue will preserve the activation state of enzymes from in vivo to in vitro. The second specific aim is to determine whether the myocardial metabolic and biochemical alterations occurring during heart failure are similar to those found after NOS blockade in normal hearts and if they can be reversed by a NO-releasing agent. The same methods in vivo and in vitro will be employed. Heart failure will be induced in dogs by chronic pacing. The third specific aim is to determine whether acute alterations of arterial substrate concentration can affect cardiac oxygen consumption during heart failure and if this effect can be reversed by NO-releasing agents. Our preliminary data indicate that FFA consumption can cause increased in cardiac O2 consumption unrelated to hemodynamic changes, but only when NO is absent. These studies will elucidate the role of NO in the pathophysiology of heart failure. This will also provide a new pharmacological mechanism of NO-donors in the treatment of heart failure. based on direct control by these agents on cardiac metabolism.