Strang L B
Department of Paediatrics, University College London, UK.
Biol Neonate. 1989;55(6):355-65. doi: 10.1159/000242939.
Early experiments by Jost and Policard demonstrated the presence of secretory activity in the lungs of the fetal rabbit. Subsequent work has demonstrated a system of active ion transport across the pulmonary epithelium of the sheep fetus, in which uphill movement of chloride ions to the pulmonary lumen provides the main force for lung liquid secretion. In the last 10-20% of gestation a reabsorptive mechanism in response to beta-adrenergic stimulation is developed which is brought into play in the perinatal period, clearing the lungs of liquid. The development of this response has been shown to require thyroid hormones. The action of adrenaline (or of a directly induced rise in intracellular cAMP) depends on the initiation of active sodium transport from the luminal side of the epithelium. Active glucose-sodium cotransport, maintaining a low glucose concentration in fetal pulmonary liquid, has also been demonstrated in this epithelium. In the postnatal period, sodium absorption continues to be a feature of the lung periphery and the epithelium of the conducting airways is known to be a site of an active ion transport system which features both chloride secretion and sodium absorption. However, this epithelium responds quite differently from the fetal peripheral epithelium to beta-adrenergic stimulation by increasing chloride secretion with little or no change in sodium absorption.
约斯特和波利卡尔早期的实验证明了胎兔肺中存在分泌活动。后续研究表明，绵羊胎儿的肺上皮存在一个主动离子转运系统，其中氯离子向肺腔的上坡运动为肺液分泌提供了主要动力。在妊娠的最后10%-20%期间，会形成一种对β-肾上腺素能刺激作出反应的重吸收机制，该机制在围产期发挥作用，清除肺中的液体。已证明这种反应的发展需要甲状腺激素。肾上腺素（或直接诱导的细胞内cAMP升高）的作用取决于上皮腔侧主动钠转运的启动。在该上皮中也已证明存在主动葡萄糖-钠共转运，可维持胎儿肺液中的低葡萄糖浓度。在出生后，钠吸收仍然是肺周边的一个特征，已知传导气道的上皮是一个主动离子转运系统的部位，其特征是既有氯离子分泌又有钠吸收。然而，该上皮对β-肾上腺素能刺激的反应与胎儿外周上皮有很大不同，它通过增加氯离子分泌而钠吸收几乎没有变化或没有变化。
