Lipoprotein distribution in sheep lung lymph.

The composition of lymph draining the sheep caudal mediastinal lymph node is believed to reflect the composition of lung interstitial fluid. Although long-term lymph fistulas have been extensively utilized in studies related to lung microvascular fluid and protein flux, attention has thus far not been focused on lipoproteins as they might appear in lung interstitial space. We therefore characterized the lipoprotein distributions and measured triglyceride and cholesterol concentrations of lung lymph and plasma in nine unanesthetized sheep with long-term embedded instrumentation. We also measured triglyceride and cholesterol concentrations in prefemoral and thoracic duct lymph. The plasma LDL concentration was 55.3 +/- 20.2 mg/dl and HDL concentration was 99.9 +/- 27.2 mg/dl. By comparison, the lung lymph LDL concentration was 27.7 +/- 3.0 mg/dl and the HDL concentration was 45.4 +/- 11 mg/dl. The major sheep lipoprotein classes (LDL, HDL), although low in concentration compared to humans, are present in lung lymph in relative proportions similar to those of plasma. Analytical ultracentrifugation revealed the presence of a fast-floating component in lung lymph HDL that was not present in plasma. Electron microscopy showed two sizes of particles in lung lymph HDL, 135A and 97A, which probably correspond to the fast-floating and slow-floating components, respectively; plasma HDL contained only 94 A particles. Changes in the physical properties of HDL present in lung lymph suggest modification of the HDL either in the endothelial barrier or interstitial fluid of the lung.