ACTIVE-TRANSPORT IN THE ALVEOLAR EPITHELIUM OF THE ADULT LUNG - VESTIGIAL OR VITAL

Active secretion by mammalian fetal pulmonary alveolar epithelium is w ell recognized, as is the role of the adult epithelium in the secretio n of surfactant. Recent studies have demonstrated active absorption by adult epithelium involving two sodium-dependent pathways. This findin g has focused attention on how poorly we understand both the dispositi on of alveolar liquid and the physiological role of surfactant. In thi s paper we review the evidence that the adult mammalian alveolar epith elium absorbs solutes by active transport, and we assess the physiolog ical importance of the resulting liquid movements.