Kobayashi K, Neely J R
J Mol Cell Cardiol. 1983 Jun;15(6):369-82. doi: 10.1016/0022-2828(83)90321-8.
The effects of increased cardiac work, pyruvate and insulin on the state of pyruvate dehydrogenase (PDH) activation and rate of pyruvate decarboxylation was studied in the isolated perfused rat heart. At low levels of cardiac work, 61% of PDH was present in the active form when glucose was the only substrate provided. The actual rate of pyruvate decarboxylation was only 5% of the available capacity calculated from the percent of active PDH. Under this condition, the rate of pyruvate decarboxylation was restricted by the slow rate of pyruvate production from glycolysis. Increasing cardiac work accelerated glycolysis, but production of pyruvate remained rate limiting for pyruvate oxidation and only 40% of the maximal active PDH capacity was used. Addition of insulin along with glucose reduced the percent of active PDH to 16% of the total at low cardiac work. This effect of insulin was associated with increased mitochondria NADH/NAD and acetyl CoA/CoA ratios. With both glucose and insulin the calculated maximum capacity of active PDH was about the same as measured rates of pyruvate oxidation indicating that pyruvate oxidation was limited by the activation state of PDH. In this case, raising the level of cardiac work increased the active PDH to 85% and although pyruvate oxidation was accelerated, measured flux through PDH was only 73% of the maximal activity of active PDH. With pyruvate as added exogenous substrate, PDH was 82% of active at low cardiac work probably due to pyruvate inhibition of PDH kinase. In this case, the measured rate of pyruvate oxidation was 64% of the capacity of active PDH. However, increased cardiac work still caused further activation of PDH to 96% active. Thus, actual rates of pyruvate oxidation in the intact tissue were determined by (1) the supply of pyruvate in hearts receiving glucose alone, (2) by the percent of active PDH in hearts receiving both glucose and insulin at low work and (3) by end-product inhibition in hearts receiving glucose and insulin at high work or at all levels of work with pyruvate as substrate. The increase in active PDH with higher levels of cardia work was associated most closely with reduced mitochondrial NADH/NAD ratios and with decreased acetyl CoA/CoA ratios when insulin or pyruvate were present.
在离体灌注大鼠心脏中，研究了增加心脏做功、丙酮酸和胰岛素对丙酮酸脱氢酶（PDH）激活状态及丙酮酸脱羧速率的影响。在低心脏做功水平下，当仅提供葡萄糖作为底物时，61%的PDH以活性形式存在。丙酮酸实际脱羧速率仅为根据活性PDH百分比计算出的可用能力的5%。在此条件下，丙酮酸脱羧速率受糖酵解产生丙酮酸的缓慢速率限制。增加心脏做功可加速糖酵解，但丙酮酸的产生对丙酮酸氧化而言仍然是限速因素，仅40%的最大活性PDH能力被利用。在低心脏做功时，同时添加胰岛素和葡萄糖可使活性PDH百分比降至总PDH的16%。胰岛素的这种作用与线粒体NADH/NAD和乙酰辅酶A/辅酶A比值增加有关。同时存在葡萄糖和胰岛素时，计算出的活性PDH最大能力与丙酮酸氧化测量速率大致相同，表明丙酮酸氧化受PDH激活状态限制。在这种情况下，提高心脏做功水平可使活性PDH增加至85%，尽管丙酮酸氧化加速，但通过PDH的测量通量仅为活性PDH最大活性的73%。添加丙酮酸作为外源性底物时，在低心脏做功时PDH活性为82%，这可能是由于丙酮酸对PDH激酶的抑制作用。在这种情况下，丙酮酸氧化测量速率为活性PDH能力的64%。然而，增加心脏做功仍会使PDH进一步激活至96%活性。因此，完整组织中丙酮酸实际氧化速率取决于：（1）仅接受葡萄糖的心脏中丙酮酸的供应；（2）低做功时同时接受葡萄糖和胰岛素的心脏中活性PDH的百分比；（3）高做功时或所有做功水平下以丙酮酸为底物同时接受葡萄糖和胰岛素的心脏中的终产物抑制作用。当存在胰岛素或丙酮酸时，较高心脏做功水平下活性PDH的增加与线粒体NADH/NAD比值降低以及乙酰辅酶A/辅酶A比值降低密切相关。
