Protein egress and entry rates in pleural fluid and plasma in sheep

We determined a rate of protein egress from the pleural cavity into thoracic duct lymph in seven anesthetized sheep in whom we had made 10-ml/kg hydrothoraces containing 1% plasma protein labeled with 125I-albumin. The labeled protein left the pleural space at an average rate of 0.02 ml X kg-1 X h-1. In 25 unanesthetized sheep we injected labeled protein intravenously and collected pleural fluid and plasma at intervals up to 48 h. The radioactivity in the sheeps' plasma fell twice as rapidly as the rate observed in humans. The half time for equilibration between plasma and pleural fluid protein specific activity was approximately 6 h. In seven sheep we gave a continuous infusion of tracer protein. In six of these seven sheep we collected superficial cervical lymph. The protein concentration in the lymph was three times that of pleural fluid. The half time for protein specific activity equilibration between plasma and pleural fluid was 5 h and 3–4 h between plasma and superficial cervical lymph. The rate of protein turnover in the pleural space appears to be much slower than previously reported.

Exchange of iodine-131-labeled chylomicron protein in vitro

Chylomicrons isolated from rat chyle were iodinated with iodine131 and the protein specific activity determined before and after incubation with normal rat serum. A marked decrease in chylomicron protein specific activity occurred during incubation because of adsorption of nonradioactive soluble serum protein as well as exchange of part of the labeled chylomicron protein with lipoprotein protein. Ultracentrifugal fractionation of serum after such incubation revealed significant radioactivity in all of the lipoprotein fractions, but with low specific activity reflecting dilution by larger protein pools. Serum proteins with density greater than 1.21 contained much less radioactivity.