Clarke I, Heasman L, Symonds M E
School of Animal and Microbial Sciences, University of Reading, Whiteknights, UK.
J Endocrinol. 1998 Feb;156(2):307-14. doi: 10.1677/joe.0.1560307.
We have previously shown that lambs delivered by caesarean section 1 week prematurely become hypothermic due to reduced brown adipose tissue function in conjunction with low plasma concentrations of cortisol and thyroid hormones. The present study therefore aimed to determine whether maternal dexamethasone (a synthetic corticosteroid) administration could improve thermoregulation in premature lambs to the extent that they become similar to term lambs. Lambs were either delivered by caesarean section into a warm (30 degrees C; WD) or cool (15 degrees C; CD) ambient temperature at 140 days of gestation, 2 days after maternal dexamethasone treatment, or at 146 days for controls. During the first 30 min of life the decline in colonic temperature was greater in dexamethasone treated lambs compared with controls delivered into the same ambient temperature. All lambs then restored colonic temperature although this adaptation took longest in dexamethasone treated lambs CD but these subsequently attained highest plateau colonic temperatures. Oxygen consumption, breathing frequency and plasma free fatty acid concentrations were highest in dexamethasone treated lambs CD. There were no differences in plasma thyroid hormones between groups, but cortisol concentrations were lower in dexamethasone treated lambs irrespective of delivery temperature. Analysis of brown adipose tissue samples at 6 h of life demonstrated that dexamethasone treated lambs WD had more uncoupling protein and, in both dexamethasone treated and control lambs, uncoupling protein content was higher in lambs CD compared with those WD. An effect of ambient temperature on thermogenic activity was only observed in the dexamethasone treated group. It is concluded that maternal dexamethasone treatment can significantly improve thermoregulation after birth following premature delivery by caesarean section. As a consequence, dexamethasone treated lambs delivered 1 week prematurely do not remain hypothermic and have higher or similar colonic temperatures compared with untreated lambs born 1-2 days before term.
我们之前已经表明，提前1周剖宫产出生的羔羊会出现体温过低的情况，这是由于棕色脂肪组织功能降低，同时血浆皮质醇和甲状腺激素浓度较低。因此，本研究旨在确定母体给予地塞米松（一种合成皮质类固醇）是否能改善早产羔羊的体温调节，使其达到与足月羔羊相似的程度。羔羊在妊娠140天、母体接受地塞米松治疗2天后，通过剖宫产分娩至温暖（30摄氏度；WD）或凉爽（15摄氏度；CD）的环境温度中，对照组则在妊娠146天分娩。在出生后的前30分钟内，与在相同环境温度下出生的对照组羔羊相比，接受地塞米松治疗的羔羊结肠温度下降幅度更大。所有羔羊随后都恢复了结肠温度，尽管这种适应过程在接受地塞米松治疗的CD组羔羊中耗时最长，但这些羔羊随后达到了最高的结肠温度平台。接受地塞米松治疗的CD组羔羊的氧气消耗量、呼吸频率和血浆游离脂肪酸浓度最高。各组之间血浆甲状腺激素没有差异，但无论分娩温度如何，接受地塞米松治疗的羔羊皮质醇浓度较低。对出生6小时的棕色脂肪组织样本分析表明，接受地塞米松治疗的WD组羔羊具有更多的解偶联蛋白，并且在接受地塞米松治疗的羔羊和对照组羔羊中，CD组羔羊的解偶联蛋白含量均高于WD组羔羊。仅在接受地塞米松治疗的组中观察到环境温度对产热活性的影响。研究得出结论，母体给予地塞米松治疗可显著改善剖宫产早产出生后羔羊的体温调节。因此，提前1周剖宫产出生且接受地塞米松治疗的羔羊不会持续体温过低，与足月前1 - 2天出生的未治疗羔羊相比，其结肠温度更高或相似。
