Modification of lymph by sheep caudal mediastinal node: effect of intranodal endotoxin

Postnodal lymph from the sheep caudal mediastinal node (CMN) is used by many investigators to assess lung vascular protein permeability. We explored the possibility that damage to the CMN blood-lymph barrier could produce increases in postnodal lymph flow and lymph-to-plasma protein concentration ratio (L/P) characteristic of lung vascular damage. Escherichia coli endotoxin (0.049 micrograms/min) was infused into a prenodal lymph vessel to the CMN in the conscious sheep, and postnodal lymph was collected for the next 7 h. Intranodal endotoxin caused an 80% increase in postnodal lymph flow and a 30% increase in postnodal L/P. Because there was no indication that the endotoxin had exerted a systemic effect, the lymph response to endotoxin was attributed to a direct effect of endotoxin on the blood-lymph barrier of the CMN. We conclude that significant increases in postnodal lymph flow and L/P characteristic of lung vascular damage can occur when the blood-lymph barrier of the CMN becomes damaged.