Solute and water transport across the pulmonary epithelium: a new chapter in lung physiology inaugurated by Alfred Jost

Abstract

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.