Pulmonary Endothelial Surface Reductase Kinetics
The role of the endothelium as a metabolically active organ having a number of regulatory functions is well established. The in vivo evaluation of these functions tends to be a difficult problem, and much of the research in this area is being carried out using simpler systems such as cultured endothelial cells. The results from such studies provide increased motivation for understanding how the various endothelial functions operate in vivo. The multiple-indicator dilution method (MID) is an approach for studying in vivo endothelial cell biology. The lungs are unique with regard to in vivo application of the MID for the study of capillary permeation, cellular transport, and reaction kinetics in that access to a single inlet (e.g., a systemic vein or the pulmonary artery) and single outlet (e.g., a peripheral systemic artery) is more readily available than in any other organ, and the MID has been applied to the in vivo study of these functions of the pulmonary endothelium (13–16, 18, 21, 22). The MID method is suited for studying those processes that occur rapidly enough that their effects can be observed in the time frame of a single pass through the lungs. In general, capillary blood flow tends to be so high in comparison to the rates of endothelial cell utilization of typical substrates for intermediary metabolism that the MID is not applicable to such substrates. However, the pulmonary endothelium also carries out a number of metabolic functions that appear to be directed at modulating blood concentrations of certain substances rather than at the metabolic requirements of the endothelial cells themselves.
KeywordsMethylene Blue Rabbit Lung American Physiological Society Reference Indicator Pulmonary Endothelium
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