Caudal mediastinal node lymph flow in sheep after histamine or endotoxin infusions.

To determine whether intrathoracic nonpulmonary structures (caudal mediastinal node or esophagus) are reputed to affect lung lymph dynamics, we studied anesthetized, open-thorax, prone, ventilated sheep in which all lung afferent lymphatics to the caudal mediastinal node were eliminated. When we increased left atrial pressure by 20 cmH2O in four sheep, there was no effect on caudal mediastinal node efferent lymph flow or protein concentration, thus providing the completeness of the surgical preparation. In four sheep, intravenous histamine infusions (3 micrograms base.kg-1.min-1) had no effect on caudal mediastinal node lymph flow or protein concentration. In seven sheep with intact lung lymphatics, Escherichia coli endotoxin infusion (1 microgram/kg over 20 min) increased lymph flow with high lymph protein concentration during the late phase (2-6 h). In seven sheep, after all lung lymphatic afferents had been cut, endotoxin did not affect caudal mediastinal node lymph flow, although lymph protein concentration was decreased in the early 0-2 h, "hypertensive") phase. We conclude that at the concentrations tested, which are those regularly used in sheep lung experiments, the effects of histamine and endotoxin on caudal mediastinal node lymph flow and protein concentration are limited to the lung.