Rat KMT‐17 fibrosarcoma‐derived endothelial cells were isolated by Percoll gradient centrifugation with an attaching‐speed separation technique, and their properties in culture were examined. The primary cultured tumor‐derived endothelial cells (TEC) showed angiotensin‐converting enzyme activity, positivity for Factor VIII‐related antigen staining, and typical capillary‐like formation on Matrigel. The primary cultured TEC monolayer showed greater permeability than normal tissuederived endothelial cell (aorta, vena cava and epididymal fat capillary) monolayers on FITC‐dextran diffusion (molecular weight 70,000). Leukocyte adhesion to TEC was reduced compared to that to fat‐derived capillary endothelial cells. These characteristics resembled those of tumor vascular endothelium, and were observed both in the primary and first‐passage cell cultures, but not in the fourth‐passage cell cultures. Our findings indicate that primary or subcultured TEC are applicable for studies of the physiological characteristics of tumor endothelial cells.

Summary Conditioned medium prepared from mouse melanoma B16 cells (B116-CM) increases the macromolecular permeability of bovine aortic, venous and human umbilical vein endothelial monolayer. Collagen, which is synthesised by endothelial cells, has an important function in regulating the permeability of endothelial monolayer. Briefly, low collagen content leads to hyperpermeable structure of the endothelial monolayer. In the present studies, we examined the relationship between the increase of endothelial permeability and content of synthesised collagen of endothelial cells cultured with B16-CM. The B16-CM reduced endothelial collagen content but did not digest collagen directly. Matrix metalloproteinase inhibitor, 1,10-phenanthroline, inhibited the increase in permeability due to addition of B16-CM. These data suggest that B16-CM acts on endothelial cells, stimulating the digestion of endothelial collagen, and that the reduced content of collagen leads to the hyperpermeability of the endothelial monolayer.

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