We examined the selectivity of the bovine pulmonary artery endothelial monolayer in vitro to molecules of different sizes. The cultured bovine pulmonary endothelial monolayer was grown on a gelatinized filter and the transendothelial transport was studied by determining the permeability of molecules ranging from 182 to 340,000 daltons under diffusion conditions. The permeabilities across the cultured bovine endothelium were modeled according to cylindrical pore theory. The data were best fit by a two-pore model with radii 65 A and 304 A and a ratio of small to large pores of 160:1. The results indicate that the cultured endothelial monolayer is a selective barrier to molecules of different sizes and that the molecular selectivity is consistent with a diffusional pathway through endothelial pore equivalents. The cultured endothelial monolayer is a useful system for studying the permeability characteristics of the endothelial barrier.

The concentration of soluble transferrin receptor (sTfR) in serum is reported to be useful in the diagnosis of iron deficiency, especially for patients with concurrent chronic disease, where routine tests of iron status are compromised by the inflammatory condition. A new diagnostic assay for sTfR is calibrated against natural plasma sTfR, thus minimizing calibration discrepancies that result from differences between the analyte and the cellular transferrin receptor used in other assays. Use of the new assay to measure sTfR concentrations in 225 healthy, hematologically normal adults provided a reference interval against which pathological samples could be compared. There was no difference in the reference intervals for men and women and no correlation of [sTfR] with the age of the subject. Black subjects had significantly higher concentrations than nonblacks, and people living at high altitude had higher concentrations than those living closer to sea level. These differences were additive.

We have developed an experimental system to measure the permeability of the cultured endothelial monolayer. The luminal-to-abluminal flux of 125I-albumin across cultured pulmonary endothelium was expressed as a clearance rate equal to the permeability-surface area product. After clearance rate measurement for a 30-min base-line period, a test agent was added to the luminal side, and the clearance rate was remeasured during a 30-min experimental period. In control studies the base-line clearance rate was 0.343 +/- 0.017 microliter/min. After correction for the diffusional resistances of the filter and unstirred layers, the calculated permeability of the endothelial monolayer was 1.2 X 10(-5) cm/s. When culture medium was the test agent, the experimental clearance rate was unchanged from the base-line value. After addition of 4 mM oleic acid to the luminal chamber, the clearance rate was 0.528 +/- 0.017 microliter/min compared with a base-line value of 0.330 +/- 0.008 microliter/min (P less than 0.005). This method allows the calculation of endothelial permeability with correction for unstirred layers and the use of each monolayer as its own control.

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Previous studies have indicated that neutrophils are required for the development of increased lung vascular permeability after thrombin-induced pulmonary microembolization. In this study, we examined neutrophil kinetics and uptake in the sheep lung before and after lung vascular injury. Sheep neutrophils were isolated by a Percoll-gradient method and labeled with indium-111 oxine. A maximum lung activity of 40% of the injected indium-111 neutrophil activity was attained 8-12 min after the injection. The calculated half-lives of both circulating and pulmonary neutrophils were 700 min. The rate of washout of labeled neutrophils from the lungs was the same as the loss of the peripheral blood activity, indicating removal of neutrophils from the lung and blood by a common pathway (e.g., liver and spleen). Intravenous infusion of alpha-thrombin resulted in an immediate uptake of neutrophils of 14% above the base-line activity. The increased uptake was associated with an immediate decrease in the blood activity, indicating sequestration of the neutrophils in the pulmonary circulation. The neutrophil uptake after alpha-thrombin was transient, reaching a maximum 15 min after infusion. Neutrophil uptake did not occur with alpha-thrombin (which lacks the fibrinogen recognition site), suggesting that the uptake was secondary to intravascular coagulation. An increase in the pulmonary blood volume cannot explain the increased neutrophil sequestration because pulmonary blood volume determined by [99mTc]pertechnetate-labeled erythrocytes did not increase after the alpha-thrombin infusion. Therefore, alpha-thrombin results in a transient neutrophil sequestration in the lung, and the response is secondary to the intravascular coagulation induced by the alpha-thrombin.