CONTROL OF METABOLISM BY NO IN THE FAILING HEART

越来越多的研究支持一氧化氮在心脏代谢控制中的作用。我们最近发现，正常犬一氧化氮合成酶(NOS)的急性阻断和起搏所致心力衰竭时NO生成量的下降都与心脏从游离脂肪酸(FFA)向碳水化合物利用的转变有关。这些现象背后的机制尚不清楚。这项研究计划将确定NO在控制心脏底物利用中的作用，以及这一作用是否在心力衰竭期间丢失。第一个具体目标是确定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，将在清醒的狗身上测量一氧化氮合酶阻断前后心脏中游离脂肪酸和碳水化合物的氧化速率。在活体实验结束时，将在冷冻夹住的心脏活组织中测量标记底物的积累以及碳水化合物和FFA氧化的关键酶的活性。组织的快速冷冻将保存从体内到体外的酶的激活状态。第二个具体目的是确定心力衰竭期间发生的心肌代谢和生化变化是否类似于一氧化氮合酶阻断正常心脏后的变化，以及NO释放剂是否可以逆转这些变化。将采用体内和体外相同的方法。慢性起搏可诱发犬心力衰竭。第三个具体目标是确定动脉底物浓度的急性变化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被NO释放剂逆转。我们的初步数据表明，FFA消耗可导致心脏耗氧量增加，与血流动力学变化无关，但仅在NO缺乏的情况下。这些研究将阐明NO在心力衰竭的病理生理学中的作用。这也将为NO供体治疗心力衰竭提供新的药理机制。基于这些药物对心脏代谢的直接控制。

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.