Simmons R A, Charlton V E
Department of Pediatrics and Cardiovascular Research Institute, University of California, San Francisco 94143.
Pediatr Res. 1990 Mar;27(3):274-7. doi: 10.1203/00006450-199003000-00014.
We have previously shown that lactate is produced by the ovine fetal lung. Inasmuch as factors that might affect lactate production, such as pulmonary glucose and oxygen uptake, change late in gestation we investigated whether pulmonary lactate metabolism also changes. Eleven chronically catheterized fetal lambs were studied over 119-141 d gestation. Lactate, glucose, and oxygen concentrations were measured in the pulmonary artery (PA) and vein while lung blood flow was determined using labeled microspheres. Between early studies (less than or equal to 127 d) and studies near term (greater than or equal to 134 d) PA lactate levels did not change, but due to increasing pulmonary blood flow, lung lactate delivery rose 51% (p less than 0.05). Because of a decline in PA glucose, lactate also made up a larger fraction of the major nonnitrogenous substrate in PA blood near term (p less than 0.001). Despite this, no net pulmonary uptake of lactate occurred. Lactate production continued, but decreased by 80% between early and late studies (p less than 0.05) and the maximum fraction of glucose uptake that could be accounted for by lactate production dropped from 0.78 to 0.20 (p less than 0.025). Correlations were found between lung lactate production and glucose uptake also correlated with PA glucose (p less than 0.05). No relationships were observed between lactate production and PA oxygen content, oxygen delivery, lactate concentration, or lactate delivery. The decreasing fraction of glucose uptake explained by lactate production suggests that metabolism of pulmonary glucose is altered near term. The correlation between decreasing glucose delivery and declining lactate production also suggests that glucose itself influences this change.
我们之前已经表明，绵羊胎儿肺会产生乳酸。鉴于可能影响乳酸产生的因素，如肺部葡萄糖摄取和氧气摄取，在妊娠后期会发生变化，我们研究了肺部乳酸代谢是否也会改变。对11只长期插管的胎羊在妊娠119 - 141天期间进行了研究。在测定肺血流量时，同时测量肺动脉（PA）和肺静脉中的乳酸、葡萄糖和氧气浓度，肺血流量通过标记微球来确定。在早期研究（小于或等于127天）和接近足月的研究（大于或等于134天）之间，肺动脉乳酸水平没有变化，但由于肺血流量增加，肺乳酸输送量增加了51%（p < 0.05）。由于肺动脉葡萄糖水平下降，在接近足月时，乳酸在肺动脉血中主要非含氮底物中所占比例也更大（p < 0.001）。尽管如此，肺部并没有发生乳酸的净摄取。乳酸继续产生，但在早期和晚期研究之间减少了80%（p < 0.05），并且可由乳酸产生所解释的葡萄糖摄取的最大比例从0.78降至0.20（p < 0.025）。发现肺乳酸产生与葡萄糖摄取之间存在相关性，且也与肺动脉葡萄糖相关（p < 0.05）。未观察到乳酸产生与肺动脉氧含量、氧输送、乳酸浓度或乳酸输送之间存在关系。由乳酸产生所解释的葡萄糖摄取比例下降表明，接近足月时肺部葡萄糖代谢发生了改变。葡萄糖输送减少与乳酸产生下降之间的相关性也表明，葡萄糖本身影响了这种变化。
