These results suggest that primary valves responsible for unidirectional interstitial fluid uptake along initial lymphatic vessels are associated with discontinuous expression of endothelial junction molecules. This feature may render the ability to separate local membrane regions between neighboring endothelial cells.

Analyses of microvascular networks with traditional tracer filling techniques suggest that the blood and lymphatic systems are distinct without direct communications, yet involvement of common growth factors during angiogenesis and lymphangiogenesis suggest that interactions at the capillary level are possible. To investigate the structural basis for lymphatic/ blood endothelial cell connections during normal physiological growth, the objective of this study was to characterize the spatial relations between lymphatic and blood capillaries in adult rat mesenteric tissue. Using immunohistochemical methods, adult male Wistar rat mesenteric tissues were labeled with antibodies against PECAM (an endothelial marker) and LYVE-1, Prox-1, or Podoplanin (lymphatic endothelial markers) or NG2 (a pericyte marker). Positive PECAM labeling identified apparent lymphatic/ blood endothelial cell connections at the capillary level characterized by direct contact or direct alignment with one another. In PECAM labeled networks, a subset of the lymphatic and blood capillary blind ends were connected with each other. Intravital imaging of FITC-Albumin injected through the femoral vein did not identify lymphatic vessels. At contact sites, lymphatic endothelial markers did not extend along blood capillary segments. However, PECAM positive lymphatic sprouts, structurally similar to blood capillary sprouts, lacked observable lymphatic marker labeling. These observations suggest that nonlumenal lymphatic/blood endothelial cell interactions exist in unstimulated adult microvascular networks and highlight the potential for lymphatic/blood endothelial cell plasticity. Anat Rec, 293:1629Rec, 293: -1638Rec, 293: , 2010. V V C 2010 Wiley-Liss, Inc.

A plaque phantom composed of a stenotic vessel wall and plaque components was successfully constructed for multicenter high resolution MRI standardization.

Lymphatic fluid uptake from the interstitium requires the primary valve system located at endothelial cell junctions. However, the exact structure of this valve system is not well established. The objective of this study was to characterize the junctional structure of endothelial cells along the hierarchy of an intact adult initial lymphatic network. Mesenteric tissues from adult male Wistar rats were labeled with antibodies against PECAM‐1 and VE‐cadherin. Endothelial cells along initial lymphatics and blood microvascular networks expressed both junctional molecules. PECAM and VE‐cadherin labeling patterns were continuous along vascular endothelial cell junctions, but discontinuous with gaps along lymphatic endothelial cell junctions. Along larger draining vessels in proximal regions of the initial lymphatic network, the majority of labeling gaps along junctions were less than 3 μm. In comparison to draining vessels, terminal lymphatics exhibited a decrease in PECAM staining intensity and a decrease in endothelial cell junctional length defined by positive PECAM and VE‐cadherin staining. These results suggest that initial lymphatics have a discontinuous expression pattern of endothelial junction molecules facilitating the ability to separate local membrane regions between neighboring endothelial cells and forming primary valve structures. Supported by NIH‐HL10881 and NIH‐T32 HL007089.