Plasticity of intercellular junctions of rat liver lymph capillaries in relation to functional conditions

The junctions between endothelial cells in lymph capillaries may have different degrees of complexity and have been classified as three types: "end to end" (EE), "overlapping" (OVL), and "interdigitating" (ID). Under normal conditions, the more complex junction types (ID and OVL) are more frequent than the simple type (EE). The authors' hypothesis was that not only the folds and digitations of the endothelial profile but also the prevalence of the more complex junction types under normal conditions impart plasticity and distensibility to the endothelial wall. To verify this hypothesis they performed a transmission electron microscope study of lymph capillaries of rat liver under normal conditions and after treatment with histamine, which induces natural filling of lymph vessels. In lymph capillaries of histamine-treated animals they found a significant prevalence of the simplest (EE) junctions (50 +/- 5% versus 20 +/- 4% in controls, p less than 0.001) over the more complex OVL (28 +/- 4% versus 57 +/- 4% in controls, p less than 0.001) and ID junctions (12 +/- 3% versus 19 +/- 4% in controls, NS). The overall trend in junction types showed a highly significant shift toward the simpler types after histamine treatment (p less than .0001). There was also a significant reduction in the mean length of adjoining cell borders from 1.5 +/- 0.1 m in histamine-treated animals (p less than 0.001). These findings indicate the participation of the junctions in variations in capacity of lymph vessels in rat liver. This mobilization of cell junctions may also favor the drainage of interstitial fluids into the absorbing lymph vessels.