Hildebrandt E, Olson M S
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760.
Biochem J. 1987 Dec 1;248(2):423-8. doi: 10.1042/bj2480423.
The oxidative decarboxylation of L-[1-14C]leucine was measured in the isolated perfused rat heart under both working and non-working conditions. Stimulation of decarboxylation of the labelled substrate was observed in working hearts as cardiac work was increased, and in Langendorff hearts upon increasing the coronary flow rate. The rate of L-[1-14C]leucine decarboxylation was significantly higher (P less than 0.05) in hearts working against moderate afterload pressure when compared to Langendorff hearts perfused at a matching coronary flow rate. The rate of release of 4-methyl-2-oxo[1-14C]pentanoate to the perfusate was high in Langendorff hearts, and was unaffected by changes in coronary flow. In contrast, perfusate levels of 14C-labelled 4-methyl-2-oxopentanoate decreased significantly upon the establishment of the working condition (P less than 0.05). These findings suggested an enhancement in the efficiency of the decarboxylation of the 2-oxo acid in response to cardiac work. The amount of branched-chain 2-oxo acid dehydrogenase complex present in the active form was measured in freeze-clamped hearts. Cardiac work resulted in a rapid activation of the complex (P less than 0.02) within 5 min of work when compared to control Langendorff hearts perfused at matching coronary flow rates. To a lesser extent, increasing the coronary flow rate in Langendorff-perfused hearts also led to activation of the enzyme complex. These studies suggest the following: a) L-leucine oxidation in myocardial tissue can be accelerated by exercise as it is in other tissues; b) this regulatory response can be evoked by the contractile activity of the heart itself, independent of contributions by circulating factors or nervous stimuli; and c) regulation of the activity state of the branched-chain 2-oxo acid dehydrogenase complex is involved in the mechanism by which metabolic flux through this pathway is controlled during cardiac work.
在工作和非工作条件下，对离体灌注大鼠心脏中L-[1-¹⁴C]亮氨酸的氧化脱羧进行了测定。在工作心脏中，随着心脏工作量增加，观察到标记底物的脱羧受到刺激；在Langendorff心脏中，随着冠状动脉流速增加，也观察到这种刺激。与以匹配冠状动脉流速灌注的Langendorff心脏相比，在承受中等后负荷压力下工作的心脏中，L-[1-¹⁴C]亮氨酸脱羧速率显著更高（P<0.05）。在Langendorff心脏中，4-甲基-2-氧代[1-¹⁴C]戊酸释放到灌注液中的速率很高，并且不受冠状动脉流速变化的影响。相反，在建立工作状态后，¹⁴C标记的4-甲基-2-氧代戊酸的灌注液水平显著降低（P<0.05）。这些发现表明，响应心脏工作，2-氧代酸脱羧效率有所提高。在冷冻钳夹的心脏中，测量了以活性形式存在的支链2-氧代酸脱氢酶复合物的量。与以匹配冠状动脉流速灌注的对照Langendorff心脏相比，心脏工作导致该复合物在工作5分钟内迅速激活（P<0.02）。在较小程度上，增加Langendorff灌注心脏中的冠状动脉流速也会导致该酶复合物的激活。这些研究表明：a）心肌组织中的L-亮氨酸氧化可像在其他组织中一样通过运动加速；b）这种调节反应可由心脏本身的收缩活动诱发，与循环因子或神经刺激的作用无关；c）支链2-氧代酸脱氢酶复合物活性状态的调节参与了在心脏工作期间控制通过该途径的代谢通量的机制。
