Cytochemical differentiation between blood and lymphatic endothelium: bovine blood and lymphatic large vessels and endothelial cells in culture

Cytochemical differentiation between blood and lymphatic endothelium has been studied only in microvessels; 5'-nucleotidase (5'Nase) has been reported to be specific for lymphatic and alkaline phosphatase (ALPase) for blood endothelium. Adenylate and guanylate cyclase (AC and GC) have recently been proposed as lymphatic endothelial markers, but conflicting data exist. This study was designed to verify the presence of these enzymes in the endothelium of large vessels and to determine whether they are retained in endothelial cells (ECs) in culture. Segments of bovine mesenteric arteries, veins, and lymphatic collectors, and EC cultures obtained by collagenase treatment of the same vessels, were assayed for 5'Nase, ALPase, AC, and GC, and were observed by transmission electron microscopy. We found ALPase activity in blood and lymphatic vessels, and this was the only enzyme activity consistently retained under culture conditions. 5'Nase was found in lymphatic but not in blood endothelium, as previously reported for microvessels. AC and GC activity was found in blood but not in lymphatic endothelium. Hence, ALPase is not a useful marker to differentiate blood from lymphatic endothelium in large vessels, whereas 5'Nase is specific for lymphatic and AC and GC for blood endothelium. It is not clear why these enzyme activities are not expressed in culture.