Tumour angiogenesis: ultrastructure of endothelial cells in mitosis.

Under the influence of a diffusible factor or factors from melanoma tumour tissue and neonatal hamster renal tissue, which passed through millipore filters, the endothelial cells of capillaries and small venules in the adult hamster were found to undergo mitotic division. Occasional endothelial cells in mitosis were noted in small arteries. Endothelial cells within the same vessel did not undergo mitosis in a synchronous fashion. During mitosis they retained intact their intercellular junctions with adjacent endothelial cells. No specific orientation of the mitotic spindle to the long axis of the vessel was noted. The usual appearance of cells in division was observed in this specific instance of endothelial cells in an adult animal undergoing mitotic division. In particular the formation of chromosomes and the various changes that ensue in the nuclear membrane were traced within endothelial cells. Typical spindle lamellae were found in cells during the formation of the membranes of the daughter nuclei.