Morphologic and DNA autoradiographic studies of the microcirculation in a transplantable rat fibrosarcoma: growth phase.

The morphology and tritiated thymidine uptake of the vascular channels in a transplantable W rat fibrosarcoma sampled at various times during growth are documented. New vessels originated primarily from normal venules in the subcutaneous tissue surrounding the neoplastic implant and grew at least twofold faster than did wound-induced vessels. During the 4-week observation period, partial maturation of vascular channels newly induced by the neoplasm was seen. This partial maturation was evidenced by an increase in the concentration of micropinocytic vesicles, a reduction in concentration and localization of intraluminal processes at or near interendothelial cell junctions, changes in the endothelial cell nuclei, and partial deposition of basement membrane material. The development of smooth muscle and nerve tissue was not seen. The proportion (13%) of labeled endothelial cells in normal subcutaneous connective tissue surrounding the 3-day-old fibrosarcoma implant was significantly higher than that seen in controls, as was the labeling index (14-25%) for endothelial cells in the fibrosarcoma up to 2 weeks after implantation. Vascular channels in the established neoplasm were examined by scanning and transmission electron microscopy and freeze-fracture techniques, and a resemblance to venular morphology was detected.