Sumida Ken D, Urdiales Jerry H, Donovan Casey M
Dept. of Biological Sciences, Chapman University, One University Dr., Orange, CA 92866.
Am J Physiol Endocrinol Metab. 2006 Jan;290(1):E185-E191. doi: 10.1152/ajpendo.00318.2004. Epub 2005 Aug 9.
The impact of reduced hepatic flow on lactate uptake and gluconeogenesis was examined in isolated glucagon-stimulated perfused livers from 24-h-fasted rats. After surgical isolation, livers were perfused (single pass) for 30 min with Krebs-Henseleit (KH) bicarbonate buffer, fresh bovine erythrocytes (hematocrit approximately 20%), and no added substrate. After this "washout" period, steady-state perfusions were initiated with a second reservoir containing the KH buffer, bovine erythrocytes, [U-(14)C]lactate (10,000 dpm/ml), lactate (2.5 mM), and glucagon (250 microg/ml). Perfusion flow rate was adjusted to one of five rates (i.e., 1.8, 2.7, 3.9, 7.4, and 11.0 ml.min(-1).100 g body wt(-1)). After the perfusion, the liver was dissected out and weighed so as to establish the actual flow rate per gram of liver. The resulting flow rates ranged from 0.52 to 4.03 ml.min(-1).g liver(-1). As a function of flow rate, lactate uptake rose in a hyperbolic fashion to an apparent plateau of 2.34 micromol.min(-1).g liver(-1). Fractional extraction (FX) of lactate from the perfusate demonstrated an exponential decline with increased flow rates (r=0.97). At flow rates above 1.0 ml.min(-1).g liver(-1), adjustments in FX compensated for changes in lactate delivery, resulting in steady rates of lactate uptake and gluconeogenesis. Below 1.0.min(-1).g liver(-1) the increased FX was unable to compensate for the decline in lactate delivery and lactate uptake declined rapidly. Gluconeogenesis demonstrated similar kinetics to lactate uptake, reflecting its dominant role among pathways for lactate removal under the current conditions.
在来自禁食24小时大鼠的分离的胰高血糖素刺激的灌注肝脏中，研究了肝血流减少对乳酸摄取和糖异生的影响。手术分离后，肝脏用克雷布斯 - 亨泽莱特（KH）碳酸氢盐缓冲液、新鲜牛红细胞（血细胞比容约20%）进行30分钟的灌注（单程），且不添加底物。在这个“洗脱”期之后，用第二个储液器开始稳态灌注，该储液器含有KH缓冲液、牛红细胞、[U-(14)C]乳酸（10,000 dpm/ml）、乳酸（2.5 mM）和胰高血糖素（250 μg/ml）。灌注流速调整为五个流速之一（即1.8、2.7、3.9、7.4和11.0 ml·min(-1)·100 g体重(-1)）。灌注后，取出肝脏称重，以确定每克肝脏的实际流速。得到的流速范围为0.52至4.03 ml·min(-1)·g肝脏(-1)。作为流速的函数，乳酸摄取呈双曲线上升，达到2.34 μmol·min(-1)·g肝脏(-1)的明显平台期。从灌注液中提取乳酸的分数提取率（FX）随着流速增加呈指数下降（r = 0.97）。在流速高于1.0 ml·min(-1)·g肝脏(-1)时，FX的调整补偿了乳酸输送的变化，导致乳酸摄取和糖异生的速率稳定。在低于1.0 min(-1)·g肝脏(-1)时，增加的FX无法补偿乳酸输送的下降，乳酸摄取迅速下降。糖异生表现出与乳酸摄取相似的动力学，反映了其在当前条件下乳酸清除途径中的主导作用。
