King J L, DiGirolamo M
Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA.
Obes Res. 1998 Jan;6(1):69-75. doi: 10.1002/j.1550-8528.1998.tb00317.x.
Lactate, an important metabolic substrate for peripheral tissues and the liver, is released in significant amounts from adipose tissue. Using a perifusion system, we measured lactate production from glucose and response to insulin in isolated mesenteric and epididymal adipocytes removed from fed or fasted male Wistar rats at two stages of growth and development: (a) lean rats (7 weeks to 9 weeks old, weighing approximately 250 g), and (b) fatter rats (6 months to 8 months old, weighing approximately 550 g). The results show that lactate production in perifused adipocytes is regulated by the prior nutritional state of the animals, by the adipose tissue region, and by the presence of insulin in the perifusate. In fat cells from lean rats, basal lactate production was significantly higher (p<0.05) in mesenteric cells when compared with epididymal cells, both in the fed state (7.8 nmo/10(7) fat cells per minute vs. 2.9 nmol/10(7) fat cells per minute) and after 2 days of fasting (13.6 nmol vs. 3.5 nmol). When the response to 1 mU/mL insulin was studied, however, the relative increase in lactate production produced by insulin was greater in the epididymal cells than in the mesenteric cells, in both the fed (194% vs. 91% over basal, respectively) and fasted (360% vs. 55% over basal, p<0.05) state. When larger epididymal adipocytes from fatter rats were compared with an equal number of smaller epididymal cells from leaner rats, the larger cells produced 4.99 nmol of lactate/10(7) fat cells per minute, whereas the smaller cells produced 2.93 nmol (p=0.08). Large fat cells showed a small and nonsignificant response to insulin in either type of cell (epididymal vs. mesenteric) or nutritional state (fed vs. fasted). This study indicates that distinct regional differences exist in lactate production and response to insulin. Mesenteric adipose tissue, which drains directly into the portal vein and provides substrates to the liver, may be an important source of lactate for the hepatic processes of gluconeogenesis and glycogenesis.
乳酸是外周组织和肝脏的一种重要代谢底物，大量从脂肪组织释放。我们使用灌流系统，测量了从处于生长发育两个阶段的 fed 或禁食雄性 Wistar 大鼠分离出的肠系膜和附睾脂肪细胞中，葡萄糖产生乳酸的情况以及对胰岛素的反应：(a) 瘦大鼠（7 周龄至 9 周龄，体重约 250 克），和 (b) 较胖大鼠（6 月龄至 8 月龄，体重约 550 克）。结果表明，灌流脂肪细胞中乳酸的产生受动物先前的营养状态、脂肪组织区域以及灌流液中胰岛素的存在调节。在瘦大鼠的脂肪细胞中，无论是在进食状态（7.8 nmo/10(7) 个脂肪细胞每分钟 vs. 2.9 nmol/10(7) 个脂肪细胞每分钟）还是禁食 2 天后（13.6 nmol vs. 3.5 nmol），肠系膜细胞中的基础乳酸产生量均显著高于附睾细胞（p<0.05）。然而，当研究对 1 mU/mL 胰岛素的反应时，无论是在进食（分别比基础值增加 194% vs. 91%）还是禁食（比基础值增加 360% vs. 55%，p<0.05）状态下，胰岛素引起的乳酸产生相对增加在附睾细胞中都大于肠系膜细胞。当将较胖大鼠的较大附睾脂肪细胞与等量较瘦大鼠的较小附睾细胞进行比较时，较大细胞每分钟产生 4.99 nmol 乳酸/10(7) 个脂肪细胞，而较小细胞产生 2.93 nmol（p = 0.08）。在任何一种细胞类型（附睾细胞与肠系膜细胞）或营养状态（进食与禁食）下，大脂肪细胞对胰岛素的反应都很小且不显著。这项研究表明，乳酸产生和对胰岛素的反应存在明显的区域差异。直接排入门静脉并为肝脏提供底物的肠系膜脂肪组织，可能是肝脏糖异生和糖原生成过程中乳酸的重要来源。
