EFFECT OF LUNG-INFLATION ON ACTIVE AND PASSIVE LIQUID CLEARANCE FROM IN-VIVO RABBIT LUNG

Active sodium transport contributes to liquid clearance from the alveo li. We hypothesized that the magnitude of active transport of alveolar liquid depends on the extent to which the alveolar epithelium is stre tched and, consequently, on the degree of alveolar inflation. In a stu dy on 38 adult rabbits, the left lung was filled in vivo with a soluti on of glucose (10 mmol/l) made isosmotic with plasma, using sodium chl oride, and held at a constant airway pressure of 3, 6, or 9 cmH(2)O fo r 6 h. Alveolar liquid clearance was measured directly as a flow into a left main bronchial catheter. Control animals were compared with ani mals in which active epithelial sodium transport was inhibited by addi ng amiloride and phloridzin (both 1 mmol/l) to the instillate. At low inflation, active sodium transport reversed a secretion of liquid into the alveoli; at high inflation, active sodium transport made little o r no contribution to transepithelial flow. Hydraulic conductance of th e left lung was 1.57 mu l.min(-1).cmH(2)O(-1).kg body wt(-1). The expe riments suggest that pulmonary inflation renders active liquid clearan ce ineffective.