Shambaugh G E, Mrozak S C, Freinkel N
Metabolism. 1977 Jun;26(6):623-35. doi: 10.1016/0026-0495(77)90084-1.
The availability and utilization of B-hydroxybutyrate as an alternate oxidative fuel during fasting hypoglycemia has been examined in the rat conceptus at 18 and 20 days gestation. A 48-hr maternal fast between days 16 and 18 or 18 and 20 resulted in a 50% fall in fetal glucose levels and a marked rise in B-hydroxybutyrate, i.e., 30-fold at 18 and 60-fold at 20 days. Tissue concentrations of B-hydroxybutyrate or acetoacetate did not exceed extracellular levels. Placenta, fetal brain, carcass, and liver all oxidized 14C-labeled B-hydroxybutyrate to 14CO2 when incubated in vitro in the presence of B-hydroxybutyrate. Highest rates of oxidation were apparent in the placenta, followed by brain, liver, and carcass. The D isomer of B-hydroxybutyrate appeared to be oxidized preferentially by all tissues studied. Despite levels of 3-ketoacid CoA transferase and acetoacetyl CoA thiolase lower at 18 than at 20 days, rates of oxidation in individual tissues incubated under identical concentrations of substrate were similar at both times. In liver and brain, increasing rates of 14CO2 generation proportionate to graded concentrations of B-hydroxybutyrate in vitro indicated that such rates were probably determined by substrate availability. B-hydroxybutyrate oxidation in extrahepatic fetal tissues was unaffected by maternal fasting. By contrast, fetal liver derived from fasted mothers generated significantly less 14CO2 from B-hydroxybutyrate than livers from fed mothers. It has been suggested that capabilities for ketone utilization are widespread in tissues of the conceptus, and that such utilization may fulfill in part the oxidative demands for continued anabolic growth during fasting hypoglycemia in the mother.
在妊娠18天和20天的大鼠胚胎中，研究了β-羟基丁酸作为禁食低血糖期间替代氧化燃料的可用性和利用率。在第16至18天或18至20天期间，母体禁食48小时导致胎儿葡萄糖水平下降50%，β-羟基丁酸显著升高，即在18天时升高30倍，在20天时升高60倍。β-羟基丁酸或乙酰乙酸的组织浓度未超过细胞外水平。当在β-羟基丁酸存在下进行体外培养时，胎盘、胎儿脑、躯体和肝脏均将14C标记的β-羟基丁酸氧化为14CO2。胎盘的氧化率最高，其次是脑、肝脏和躯体。在所研究的所有组织中，β-羟基丁酸的D异构体似乎优先被氧化。尽管18天时3-酮酸辅酶A转移酶和乙酰乙酰辅酶A硫解酶的水平低于20天时，但在相同底物浓度下培养的各个组织的氧化率在这两个时间相似。在肝脏和脑中，体外14CO2生成速率随β-羟基丁酸分级浓度增加，表明此类速率可能由底物可用性决定。胎儿肝外组织中的β-羟基丁酸氧化不受母体禁食的影响。相比之下，来自禁食母体的胎儿肝脏从β-羟基丁酸产生的14CO2明显少于来自喂食母体的肝脏。有人提出，酮利用能力在胚胎组织中广泛存在，并且这种利用可能部分满足母体禁食低血糖期间持续合成代谢生长的氧化需求。
